Arctic Sea Ice : Forum

AGW in general => Science => Topic started by: Ned W on August 20, 2018, 02:57:23 PM

Title: Comparison: forcings from CO2, CH4, N2O
Post by: Ned W on August 20, 2018, 02:57:23 PM
From time to time on ASIF (e.g. here (https://forum.arctic-sea-ice.net/index.php/topic,1053.msg168379.html#msg168379)) there seems to be some mistaken ideas about the relative importance of CO2 vs methane.

Over the past three-plus decades, the annual change in forcing from CO2 has consistently been much larger than from methane (or N2O, for that matter):

(https://i.imgur.com/YqfIUeZ.png)

In fact, the gap between them is growing, not shrinking.  The trend in this gap (dF_CO2 minus dF_CH4) is statistically significant.  From 1985 to 2017 it increased by approximately 77%. 

At this point in time, the increase in the methane forcing is simply not very important compared to the increase in the CO2 forcing.

The fine print:  Data from here (http://ftp://aftp.cmdl.noaa.gov/products/trends/co2/co2_annmean_gl.txt), here (http://ftp://aftp.cmdl.noaa.gov/products/trends/ch4/ch4_annmean_gl.txt), and here (http://ftp://ftp.cmdl.noaa.gov/hats/n2o/combined/HATS_global_N2O.txt).  All forcings calculated using the updated models from Etminan et al. (2016) (https://agupubs.onlinelibrary.wiley.com/doi/full/10.1002/2016GL071930). 
Title: Re: Comparison: forcings from CO2, CH4, N2O
Post by: Ned W on August 20, 2018, 03:26:13 PM
Looking back in time, this is a continuation of a longer-term trend.  In 1950, the annual increases in forcings from CO2 and methane were basically equal.  But the CO2 forcing increased rapidly, while the methane forcing increased more slowly.

This graph uses the annual concentrations from CMIP5 here (http://www.pik-potsdam.de/~mmalte/rcps/) up to 2005, and NOAA compilations for 2006-present (see previous post for sources).   All have been converted to annual increases in forcing using the updated models from Etminan et al. (2016) (https://agupubs.onlinelibrary.wiley.com/doi/full/10.1002/2016GL071930).  :

(https://i.imgur.com/2LbtjvH.png)

For some reason there's a disproportionate emphasis on methane here on ASIF.  It was very important in the past but over the next few decades it will be basically trivial in comparison to the warming from CO2.

------------------
Edited to add:  I verified my calculations of forcings by comparison with Table S1 from the supplementary information of Etminan et al. (https://agupubs.onlinelibrary.wiley.com/action/downloadSupplement?doi=10.1002%2F2016GL071930&file=grl55302-sup-0001-Supplementary.pdf)  The calculations match nicely for all three gases.
Title: Re: Comparison: forcings from CO2, CH4, N2O
Post by: Ned W on August 20, 2018, 04:30:25 PM
One more post. 

Papers like this are cited as reason to be alarmed about methane releases from the Arctic:

Quote
Schneider von Deimling, T., Grosse, G., Strauss, J., Schirrmeister, L., Morgenstern, A., Schaphoff, S., Meinshausen, M., and Boike, J.: Observation-based modelling of permafrost carbon fluxes with accounting for deep carbon deposits and thermokarst activity, Biogeosciences, 12, 3469-3488, doi:10.5194/bg-12-3469-2015, 2015.

http://www.biogeosciences.net/12/3469/2015/bg-12-3469-2015.html (http://www.biogeosciences.net/12/3469/2015/bg-12-3469-2015.html)

But at the global scale, the impact of that is relatively small.  Per Table 3, the total additional warming from newly thawed permafrost is 0.03 C in 2050, and 0.06 to 0.09 C in 2100 (depending on RCP pathway).  And a majority of that is from CO2, not methane. 

So according to that paper, the global warming attributable to *methane* from newly thawing permafrost in 2050 and 2100 will be around 1% of the total predicted warming across each RCP scenario.

Sure, it's worth studying.  But keep in mind that what you're talking about is approximately 1% of the overall problem.
Title: Re: Comparison: forcings from CO2, CH4, N2O
Post by: wili on August 20, 2018, 04:50:12 PM
Ned, first, please state specifically who said exactly that this article was "a reason to be alarmed about methane releases from the Arctic"

Second, I am having trouble accessing the tables from this article. Could you link them or copy them here? Your claims about what they say seem to not jibe with how Science Daily covered the article:

Quote
Existing models currently attribute about 20 percent of the permafrost carbon feedback this century to methane, with the rest due to carbon dioxide from terrestrial soils. By including thermokarst lakes, methane becomes the dominant driver, responsible for 70 to 80 percent of permafrost carbon-caused warming this century.

Adding thermokarst methane to the models makes the feedback’s effect similar to that of land-use change, which is the second-largest source of human-made warming.

But maybe I'm missing something?

And finally, thank you for your admission that: "Sure, it's worth studying"

Perhaps a bit of an understatement, though?

I'm sure we can agree that slashing CO2 emissions as quickly and as deeply as possible is the thing that is of central importance. But looking at the plethora of feedbacks waiting in the wings or already kicking in certainly seems to be a responsible and relevant thing to do, right? Especially as every GW exacerbating ('positive') feedback also feeds back on all the others in a dizzyingly complex way...
Title: Re: Comparison: forcings from CO2, CH4, N2O
Post by: Ned W on August 20, 2018, 05:17:48 PM
It's a general pattern across several threads, several posters, and various similar papers. 

Here's Table 2:

(https://i.imgur.com/TGF5Mz6.png)

Note the additional warming values listed in 2050 (0.03 C) and in 2100 (0.06 to 0.09 C).  Using the CMIP5 multimodel means (downloaded from KNMI Climate Explorer), the additional warming represents around 3% of the CMIP5-projected warming in 2050 and 2100 across the four RCP pathways.

Meanwhile, section 3.4 of the paper states that:

Quote
Despite CH4 release contributing only a few percent to total permafrost carbon release, our analyses suggest that it can cause up to about 40 % (upper 68 % range) of permafrost-affected warming.

So the total additional warming from this source (CO2 plus methane) is about 3% of all projected warming, but the methane fraction is 40% or smaller ... so around 1% of the global mean temperature change, as I said.

I do think it's worth studying.  But methane from thawing permafrost is just not all that big a factor for the globe as a whole. 
Title: Re: Comparison: forcings from CO2, CH4, N2O
Post by: gerontocrat on August 20, 2018, 05:31:52 PM

I'm sure we can agree that slashing CO2 emissions as quickly and as deeply as possible is the thing that is of central importance. But looking at the plethora of feedbacks waiting in the wings or already kicking in certainly seems to be a responsible and relevant thing to do, right? Especially as every GW exacerbating ('positive') feedback also feeds back on all the others in a dizzyingly complex way...

Full article at https://www.nature.com/articles/s41467-018-05738-9 (open access)

and this is what the paper concludes...
Quote
The moderate climate mitigation strategy (RCP4.5) requires a > 50% reduction in anthropogenic CO2 emissions (i.e., −20 Gt CO2 yr−1) by 2100 compared to the current level61. Our projected permafrost emissions are comparatively small (1.5–4.2 Gt CO2e yr−1 by 2100 for RCP4.5 and 8.5, respectively). However, they are of similar magnitude to the second most important anthropogenic source after fossil fuels [Land Use Change emissions 3.5 ± 1.8 Gt CO2 yr−1], which has been relatively constant during the last 60 years62, implying that our projected permafrost emissions will provide a headwind in the goal to aggressively mitigate CO2 emissions.

Yet another +ve feedback. There is a grave shortage of studies showing -ve feedbacks.
Title: Re: Comparison: forcings from CO2, CH4, N2O
Post by: Ned W on August 20, 2018, 05:52:11 PM
Your claims about what they say seem to not jibe with how Science Daily covered the article

That Science Daily quote was about a different paper (https://www.nature.com/articles/s41467-018-05738-9), not the one I cited (though some of the same authors were on both papers). 

From that other paper (Katey Walter Anthony et al.) the additional radiative forcing (relative to 1950) from "abrupt permafrost thaw beneath thermokarst lakes" is as follows:

2050:  +0.030 or 0.032 W/m2 (depending on method) for RCP 8.5
2100:  +0.066 or 0.137

Meanwhile, the CMIP5 radiative forcing under RCP 8.5 (relative to 1950) is:

2050: +3.77 W/m2
2100: +7.50

So ... the additional RF from thermokarst lakes, according to the Katey Walter Anthony et al. paper, is about 1.3% of the overall (global) forcing.  The KWA paper also provides the fraction that is due to methane:

2050: 70% (under RCP 8.5)
2100: 64%

So the methane fraction of RF from "abrupt permafrost thaw beneath thermokarst lakes" would be around 0.9% of the global total RF.
Title: Re: Comparison: forcings from CO2, CH4, N2O
Post by: Ned W on August 20, 2018, 06:17:04 PM
Yet another +ve feedback. There is a grave shortage of studies showing -ve feedbacks.

There are some; for example:

Climate mitigation from vegetation biophysical feedbacks during the past three decades (https://www.nature.com/articles/nclimate3299)

How important is carbon storage by southern polar benthos as a negative feedback on climate change?  (http://epic.awi.de/45188/)

Interactive ozone induces a negative feedback in CO2‐driven climate change simulations (https://agupubs.onlinelibrary.wiley.com/doi/abs/10.1002/2013JD020575)

Large‐scale ocean circulation‐cloud interactions reduce the pace of transient climate change (https://agupubs.onlinelibrary.wiley.com/doi/abs/10.1002/2016GL067931)

Mechanisms of the Negative Shortwave Cloud Feedback in Middle to High Latitudes (https://journals.ametsoc.org/doi/abs/10.1175/JCLI-D-15-0327.1)

etc. 

That said, my qualitative impression is that negative feedbacks on climate are less important (aside from the obvious and already well-understood Planck feedback).  But they probably also tend to be discussed less here, because we (collectively) do like to focus on the idea that The World Is Going To Hell In A Handbasket.
Title: Re: Comparison: forcings from CO2, CH4, N2O
Post by: GoSouthYoungins on August 20, 2018, 06:27:59 PM
I feel like I'm taking crazy pills. How does it make any sense calculating ANNUAL change in forcing, using a number derived from a 100 year time scale? Maybe I'm missing something, but why is the GWP1 never discussed? Would that not be a more appropriate number to calculate annual forcing that GWP100?
Title: Re: Comparison: forcings from CO2, CH4, N2O
Post by: Ned W on August 20, 2018, 06:58:16 PM
I feel like I'm taking crazy pills. How does it make any sense calculating ANNUAL change in forcing, using a number derived from a 100 year time scale? Maybe I'm missing something, but why is the GWP1 never discussed? Would that not be a more appropriate number to calculate annual forcing that GWP100?

RF isn't derived from GWP. 
Title: Re: Comparison: forcings from CO2, CH4, N2O
Post by: GoSouthYoungins on August 20, 2018, 07:15:49 PM
I feel like I'm taking crazy pills. How does it make any sense calculating ANNUAL change in forcing, using a number derived from a 100 year time scale? Maybe I'm missing something, but why is the GWP1 never discussed? Would that not be a more appropriate number to calculate annual forcing that GWP100?

RF isn't derived from GWP.

Ya, it's an input for GWP. So whats CH4's GWP1? It's the question I've asked a dozen times in various threads, and no one is interested...why?
Title: Re: Comparison: forcings from CO2, CH4, N2O
Post by: kassy on August 20, 2018, 07:32:51 PM
See

https://www.epa.gov/ghgemissions/understanding-global-warming-potentials

It varies on the time scale you look at.
And then there is a range of estimates.

You could easily summarize it as methane is bad especially as a feedback loop.
Title: Re: Comparison: forcings from CO2, CH4, N2O
Post by: Ned W on August 20, 2018, 07:47:32 PM
So whats CH4's GWP1? It's the question I've asked a dozen times in various threads, and no one is interested...why?

Probably because it ignores all the warming that happens after that first year is over.  The entire point of GWP is to account for the integrated warming produced by a molecule of gas X over a long period of time.

You could easily summarize it as methane is bad especially as a feedback loop.

Well, again, see the first two posts in this thread.  On a global scale, methane is currently pretty minor compared to CO2, and the gap is actually widening -- radiative forcing from CO2 is increasing faster than radiative forcing from methane. 
Title: Re: Comparison: forcings from CO2, CH4, N2O
Post by: GoSouthYoungins on August 20, 2018, 08:12:37 PM
So whats CH4's GWP1? It's the question I've asked a dozen times in various threads, and no one is interested...why?

Probably because it ignores all the warming that happens after that first year is over.  The entire point of GWP is to account for the integrated warming produced by a molecule of gas X over a long period of time.

You could easily summarize it as methane is bad especially as a feedback loop.

Well, again, see the first two posts in this thread.  On a global scale, methane is currently pretty minor compared to CO2, and the gap is actually widening -- radiative forcing from CO2 is increasing faster than radiative forcing from methane.

I'm not the dullest tack on the board, but I can't mentally integrate this information to my understanding of the climate system. If you are calculating how much warming happens in a year, shouldn't that inherently ignore all the warming that will happen after that, and solely concentrate on that year?

If the GWP1 of CH4 is 100X CO2, and since pre industrial CH4 has gone up 1200 ppb (or 1.2 ppm) isn't that the equivalent of a 120 ppm increase of CO2? Where is the fault in this logic?
Title: Re: Comparison: forcings from CO2, CH4, N2O
Post by: A-Team on August 20, 2018, 08:20:48 PM
Is that so?

@ZLabe
Monthly atmospheric global methane (CH₄; potent greenhouse gas) through 2017

https://www.esrl.noaa.gov/gmd/ccgg/trends_ch4/#global
Title: Re: Comparison: forcings from CO2, CH4, N2O
Post by: Ned W on August 20, 2018, 08:30:04 PM
If you are calculating how much warming happens in a year, shouldn't that inherently ignore all the warming that will happen after that, and solely concentrate on that year?

Each CO2 molecule sticks around longer and continues adding to the warming.

As a simple example, consider two gases, X and Y.  Gas X has a lifetime of 1 year, gas Y has a two-year lifetime.  Emissions for each start at 1 unit and increase by 1 unit per year:

Emissions:
Year 1: X = 1, Y = 1
Year 2: X = 2, Y = 2
Year 3: X = 3, Y = 3
Year 4: X = 4, Y = 4
Year 5: X = 5, Y = 5

Atmospheric concentration for gas X is always the same as emissions -- because each molecule disappears after one year.  But for gas Y, concentration is the sum of the two most recent years' emissions, because it sticks around for two years:

Atmospheric concentration:
Year 1: X = 1, Y = 1
Year 2: X = 2, Y = 3
Year 3: X = 3, Y = 5
Year 4: X = 4, Y = 7
Year 5: X = 5, Y = 9

So, to answer your question: Let's say you are interested in the warming that occurs in year 3.  You are correct that you don't need to know about warming that occurs a year later (year 4).  But you do need to know about warming caused by molecules emitted a year earlier (year 2) because in the case of gas Y, molecules emitted during year 2 are still producing warming during year 3.
Title: Re: Comparison: forcings from CO2, CH4, N2O
Post by: wili on August 20, 2018, 08:30:16 PM
"Science Daily quote was about a different paper, not the one I cited"

Thanks for the clarification, Ned. I should have checked!  :-[
Title: Re: Comparison: forcings from CO2, CH4, N2O
Post by: gerontocrat on August 20, 2018, 08:51:18 PM
Yet another +ve feedback. There is a grave shortage of studies showing -ve feedbacks.

There are some; for example:

Climate mitigation from vegetation biophysical feedbacks during the past three decades (https://www.nature.com/articles/nclimate3299)
How important is carbon storage by southern polar benthos as a negative feedback on climate change?  (http://epic.awi.de/45188/)
Interactive ozone induces a negative feedback in CO2‐driven climate change simulations (https://agupubs.onlinelibrary.wiley.com/doi/abs/10.1002/2013JD020575)
Large‐scale ocean circulation‐cloud interactions reduce the pace of transient climate change (https://agupubs.onlinelibrary.wiley.com/doi/abs/10.1002/2016GL067931)
Mechanisms of the Negative Shortwave Cloud Feedback in Middle to High Latitudes (https://journals.ametsoc.org/doi/abs/10.1175/JCLI-D-15-0327.1)

That said, my qualitative impression is that negative feedbacks on climate are less important (aside from the obvious and already well-understood Planck feedback).  But they probably also tend to be discussed less here, because we (collectively) do like to focus on the idea that The World Is Going To Hell In A Handbasket.
Thanks Ned W,

Followed your links and ended up here..
https://www.gfdl.noaa.gov/bibliography/related_files/bjs0601.pdf
An Assessment of Climate Feedbacks in Coupled Ocean–Atmosphere Models

and have to say that excluding the Planck, it does not look so good.

But maybe it will be the forcing effects from human activities that will do for us. E.g.s mitigation from the greening of earth can't happen if we chop everything down, co2 sequestration from animals living in new habitats in the polar regions won't happen if we have eaten the food chain.

But going off-topic. halt!
Title: Re: Comparison: forcings from CO2, CH4, N2O
Post by: TeaPotty on August 20, 2018, 09:52:26 PM
Is this thread concern trolling, Ned?

Of course CH4 is tiny today compared to CO2 forcing. But CH4 levels are accelerating, we know of many CH4 feedbacks waiting to kick in, and we are already seeing significant reductions in atmospheric OH (Hydroxyl Radicals) necessary to break down CH4.

CH4 will be a very big factor in decades to come. This is now almost fact, Ned.
Title: Re: Comparison: forcings from CO2, CH4, N2O
Post by: GoSouthYoungins on August 20, 2018, 10:09:48 PM
Is that so?

@ZLabe
Monthly atmospheric global methane (CH₄; potent greenhouse gas) through 2017

https://www.esrl.noaa.gov/gmd/ccgg/trends_ch4/#global

It seems like this is in response to my post. It doesn't totally make sense, but I can't figure out what other post it would be regarding. What are you getting at? Do you believe that industry began in 1983?
Title: Re: Comparison: forcings from CO2, CH4, N2O
Post by: GoSouthYoungins on August 20, 2018, 10:14:28 PM
Is this thread concern trolling, Ned?

Of course CH4 is tiny today compared to CO2 forcing. But CH4 levels are accelerating, we know of many CH4 feedbacks waiting to kick in, and we are already seeing significant reductions in atmospheric OH (Hydroxyl Radicals) necessary to break down CH4.

CH4 will be a very big factor in decades to come. This is now almost fact, Ned.

CH4 forcing today tiny compared to CO2? REALLY? 1.9 ppm vs 410 ppm. 100 times more potent (conservatively) means it is almost half as strong a forcing as C02. I guess you could think as that as tiny, but not to me.
Title: Re: Comparison: forcings from CO2, CH4, N2O
Post by: TeaPotty on August 20, 2018, 10:21:08 PM
CH4 forcing today tiny compared to CO2? REALLY? 1.9 ppm vs 410 ppm. 100 times more potent (conservatively) means it is almost half as strong a forcing as C02. I guess you could think as that as tiny, but not to me.

I guess tiny is the wrong word. It would be be interesting to see a graph comparing raw forcing.

In any case, CH4 will undeniably be a major climate change factor in the future.
Title: Re: Comparison: forcings from CO2, CH4, N2O
Post by: Ned W on August 20, 2018, 10:39:41 PM
1.9 ppm vs 410 ppm. 100 times more potent (conservatively) means it is almost half as strong a forcing as C02.

That ... Is not how this works.  Sorry.

It would be be interesting to see a graph comparing raw forcing.

See the first two posts of this thread, which compare forcings from CO2, Methane, and N2O. 

CH4 isn't necessarily "tiny", but even the total global CH4 forcing -- which includes non-Arctic sources, e.g. the tropics -- is pretty small compared to CO2.
Title: Re: Comparison: forcings from CO2, CH4, N2O
Post by: magnamentis on August 20, 2018, 10:51:10 PM
1.9 ppm vs 410 ppm. 100 times more potent (conservatively) means it is almost half as strong a forcing as C02.

That ... Is not how this works.  Sorry.

It would be be interesting to see a graph comparing raw forcing.

See the first two posts of this thread, which compare forcings from CO2, Methane, and N2O. 

CH4 isn't necessarily "tiny", but even the total global CH4 forcing -- which includes non-Arctic sources, e.g. the tropics -- is pretty small compared to CO2.

isn't the main risk coming from CH4 the huge "dormant" part that depending on temperature developments at depth and in permafrost regions can kind of blow out in mass within very short future time periods. at least this has been my impression when reading about CH4 over the last 10-15 years.
Title: Re: Comparison: forcings from CO2, CH4, N2O
Post by: AbruptSLR on August 20, 2018, 11:08:24 PM
The total radiative forcings, RFs, from the linked ORNL website article by Blasing, T.J. (that updates such RF values reported in April 2016) are used in the linked Wikipedia article to calculate a CO2e value of 526.6ppm:

https://en.wikipedia.org/wiki/Carbon_dioxide_equivalent


Extract: "To calculate the CO2e of the additional radiative forcing calculated from April 2016's updated data: ∑ RF(GHGs) = 3.3793, thus CO2e = 280 e3.3793/5.35 ppmv = 526.6 ppmv."

http://cdiac.ornl.gov/pns/current_ghg.html

Per the following linked NOAA website the change in CO2e in 2017 was 4 ppm, which would give a total CO2e at the end of 2017 of about 530.6 ppm

https://www.esrl.noaa.gov/gmd/aggi/aggi.html

This value of 530.6 ppm for CO2e for 2017 is well above the 425ppm value assumed by RCP 8.5 (used to force climate models for AR5, see the attached image).
Title: Re: Comparison: forcings from CO2, CH4, N2O
Post by: GoSouthYoungins on August 20, 2018, 11:37:52 PM
1.9 ppm vs 410 ppm. 100 times more potent (conservatively) means it is almost half as strong a forcing as C02.

That ... Is not how this works.  Sorry.

It would be be interesting to see a graph comparing raw forcing.

See the first two posts of this thread, which compare forcings from CO2, Methane, and N2O. 

CH4 isn't necessarily "tiny", but even the total global CH4 forcing -- which includes non-Arctic sources, e.g. the tropics -- is pretty small compared to CO2.

Alright, then explain to me how it works, in plain english. Or at least tell me what is wrong with the way I am describing it.

CH4 atmospheric life = 12.4 years;  GWP100 equal 28. 100/12.4 = 8;  28*8 = 224. Why is that wrong? This is by no means my area of expertise, but if you actually understand it, you should be able to explain it. And if you can explain it, I will be able to understand it.
Title: Re: Comparison: forcings from CO2, CH4, N2O
Post by: GoSouthYoungins on August 21, 2018, 12:01:20 AM
The total radiative forcings, RFs, from the linked ORNL website article by Blasing, T.J. (that updates such RF values reported in April 2016) are used in the linked Wikipedia article to calculate a CO2e value of 526.6ppm:

https://en.wikipedia.org/wiki/Carbon_dioxide_equivalent


Extract: "To calculate the CO2e of the additional radiative forcing calculated from April 2016's updated data: ∑ RF(GHGs) = 3.3793, thus CO2e = 280 e3.3793/5.35 ppmv = 526.6 ppmv."

http://cdiac.ornl.gov/pns/current_ghg.html

Per the following linked NOAA website the change in CO2e in 2017 was 1.6 ppm, which would give a total CO2e at the end of 2017 of about 528.2 ppm

https://www.esrl.noaa.gov/gmd/aggi/aggi.html

This value of 528.2ppm for CO2e for 2017 is well above the 425ppm value assumed by RCP 8.5 (used to force climate models for AR5, see the attached image).

Do the math yourself. They are clearly using a multiplier of 28 for CH4. This understates the current effect methane is have 8 ****ING FOLD.

CO2e is closer to 700, LLOL. (My best friend from college had an australian father who used to say, "Laugh and the world laughs with you, cry and you cry alone.)
Title: Re: Comparison: forcings from CO2, CH4, N2O
Post by: Ned W on August 21, 2018, 04:15:50 AM
No, no, no.  We went over this exact point last year, and now ASLR is repeating the same incorrect claims. 

The big problem is that he's comparing apples to oranges.  ASLR cites Wikipedia as evidence that something called "CO2e" ("CO2 equivalent") was 528 ppmv (in 2017) and uses this to suggest that the IPCC's CMIP5 RCP 8.5 forcings are too low because their value for "CO2e" was projected to be only 425 ppmv in 2017.

That would be dramatic indeed -- the IPCC's fastest-warming scenario is already 100 ppmv too low after only a few years?!  But this is a fundamentally dishonest comparison.  ASLR is comparing numbers from two very different definitions of "CO2e":

* ASLR's Wikipedia number (528 ppmv) is based only on forcing from greenhouse gases. 

* ASLR's RCP 8.5 number (425 ppmv) is based on all anthropogenic forcings -- greenhouse gases, aerosols, black carbon, land-use albedo, everything.

What ASLR is doing is quite literally equivalent to suggesting that the IPCC has erroneously calculated the area of New York [city] because its number is much smaller than Wikipedia's value for the area of New York [state].   Yeah, they're both called "New York" but the numbers are based on two different definitions of "New York". 

That's the main problem with ASLR's comment.  The other curious thing is his reliance on an anonymous Wikipedia user for a greenhouse-gas-based value of CO2e (528 ppmv).  I could say more about that, but this comment is already too long and we went over all this a year ago already.

The total radiative forcings, RFs, from the linked ORNL website article by Blasing, T.J. (that updates such RF values reported in April 2016) are used in the linked Wikipedia article to calculate a CO2e value of 526.6ppm:

https://en.wikipedia.org/wiki/Carbon_dioxide_equivalent


Extract: "To calculate the CO2e of the additional radiative forcing calculated from April 2016's updated data: ∑ RF(GHGs) = 3.3793, thus CO2e = 280 e3.3793/5.35 ppmv = 526.6 ppmv."

http://cdiac.ornl.gov/pns/current_ghg.html

Per the following linked NOAA website the change in CO2e in 2017 was 1.6 ppm, which would give a total CO2e at the end of 2017 of about 528.2 ppm

https://www.esrl.noaa.gov/gmd/aggi/aggi.html

This value of 528.2ppm for CO2e for 2017 is well above the 425ppm value assumed by RCP 8.5 (used to force climate models for AR5, see the attached image).
Title: Re: Comparison: forcings from CO2, CH4, N2O
Post by: GoSouthYoungins on August 21, 2018, 04:48:51 AM

That would be dramatic indeed -- the IPCC's fastest-warming scenario is already 100 ppmv too low after only a few years?!  But this is a fundamentally dishonest comparison.  ASLR is comparing numbers from two very different definitions of "CO2e":

* ASLR's Wikipedia number (528 ppmv) is based only on forcing from greenhouse gases. 

* ASLR's RCP 8.5 number (425 ppmv) is based on all anthropogenic forcings -- greenhouse gases, aerosols, black carbon, land-use albedo, everything.

What ASLR is doing is quite literally equivalent to suggesting that the IPCC has erroneously calculated the area of New York [city] because its number is much smaller than Wikipedia's value for the area of New York [state].   Yeah, they're both called "New York" but the numbers are based on two different definitions of "New York". 


1) Thanks for not answering my simple question. I guess you don't understand it, at least not well enough to explain it.

2)Much more important to slander ASLR. Notice how he doesn't actually make an hard apples to apples, but instead simply states a correct fact... "This value of 528.2ppm for CO2e for 2017 is well above the 425ppm value assumed by RCP 8.5" True it is a bit misleading, but intellectually dishonest? What's intellectually dishonest is your willingness to say that my math is wrong, but not be willing to show what the correct math is. My guess is that you can't, but you read the papers and the papers conclusion differs from mine, so you just go with that.

Title: Re: Comparison: forcings from CO2, CH4, N2O
Post by: Viggy on August 21, 2018, 06:25:52 AM
Um ... what is the point of this thread and why is the DELTA in annual forcing a relevant metric?

CH4 lasts in the atmosphere for 10-12 years after which it converts to CO2 and H2O. CO2 lasts for 200-ish years. The delta in annual forcing for CH4 will obviously stay close to 0, if the same amount of CH4 is released today, as was released 10-12 yrs ago.

Delta in annual forcing is a somewhat pointless metric when you compare compounds with such massively varying lifespans. You provided as evidence, a 40 year graph comparing the RF of a compound that decays in 12 yrs and 200 yrs.


Methane release from the Arctic is an insanely important metric because there is more buried methane hydrate than the world's oil, gas and coal resources combined. A sudden release of even a fraction of this, will cause the 'ridiculous' change in forcing metric to skyrocket.

Additionally, nuanced topics cannot be reduced to 1 simple graph. For example, the IPCC report clearly states that every 1% increase in methane released, causes a 0.32% decrease in OH which is necessary to convert methane to CO2 and H2O. This is also a feedback loop, more methane released, the longer it stays in the atmosphere.
Title: Re: Comparison: forcings from CO2, CH4, N2O
Post by: sidd on August 21, 2018, 06:53:29 AM
Mr Ned W is correct.

land use and aerosols (and some others) subtract in the IPCC number. wiki does not consider those.

sidd
Title: Re: Comparison: forcings from CO2, CH4, N2O
Post by: oren on August 21, 2018, 07:39:43 AM
Ned, why not post a chart of the current total radiative forcing of all GHGs, instead of just the annual delta?
Then we can judge for ourselves how negligible each gas is.
GSY, I think global warming potential, GWP is the sum, over the atmospheric lifetime of a molecule, of its radiative forcing RF.
Title: Re: Comparison: forcings from CO2, CH4, N2O
Post by: Ned W on August 21, 2018, 11:57:03 AM
I'm not convinced that a real understanding of the mathematical meaning of the term "radiative forcing" is as widespread on ASIF as it ought to be.

For a greenhouse gas, a "radiative forcing" (RF) is simply the change in the Earth's radiation balance when the concentration of that gas changes from some initial value c0 to a different value c1.

Time, per se, is utterly irrelevant to this definition [1].  The times at which c0 and c1 are measured don't matter.  They could be millions of years apart.  Or c0 and c1 could be purely hypothetical, for thought experiments about how much warming would occur under different concentrations of gases.  All that matters are the actual concentrations present in the atmosphere at times c0 and c1.

Mathematically, the forcing from 1765 to present is literally identical to the sum of the forcing from 1765-1766 plus the forcing from 1766-1767 plus the forcing from 1767-1768 plus ... up to the forcing from 2017-2018.  Literally, you can calculate the individual one-year forcings and add them up over some longer period of time and you'll get the same result as if you calculated the forcing for that longer period of time directly using its starting and ending concentrations.

Most of us are used to reading about RF in the context of a change from pre-industrial (say, 1765) to now.  In that case, c0 is the concentration in 1765 and c1 is the concentration today.  But there's nothing special about using 1765's concentration as the baseline. 

And in fact if you do use 1765 as the baseline (c0) value, it loses the ability to differentiate between the effects of changing concentrations within that 250-year time window.  If we want to understand what is happening in the atmosphere in recent years, using 1765's concentration as the baseline will obscure that, because the resulting forcing includes changes that happened a century ago.

So, it's incorrect to think of 1765-present as some kind of "true" radiative forcing and 2016-2017 as some kind of sketchy "delta" that isn't a "true" radiative forcing. Anyone inclined to doubt me on this should check out Table S1 from Etimnan et al. (2016), in which the authors use a roughly 2011-ish set of CO2, CH4, and N2O concentrations as the baseline and then calculate the radiative forcings for all kinds of crazy hypothetical combinations of the three gases.

[1] The standard version of RF that I am using here includes the stratospheric temperature adjustment resulting from the change in concentrations.  If the time elapsed between when concentrations c0 and c1 are measured is extremely short, a literalist interpretation of the meaning of this RF would be incorrect.  But that's really only of academic interest.
Title: Re: Comparison: forcings from CO2, CH4, N2O
Post by: gerontocrat on August 21, 2018, 12:48:58 PM
I can't say I am much clearer about RF after all that. So I stick with the NOAA emissions data and their calculation from that of their AGGI measure.

The only cautionary note I have is the measure of CH$ emissions given the absence of sampling stations in the tundra and over the shallow waters of Arctic shelves.
Title: Re: Comparison: forcings from CO2, CH4, N2O
Post by: Ned W on August 21, 2018, 01:01:26 PM
I can't say I am much clearer about RF after all that.

Sorry.  It's not the easiest thing to explain, and is perhaps not all that intuitive.  I'll keep thinking about how to clarify it.

Quote
So I stick with the NOAA emissions data and their calculation from that of their AGGI measure.

The only cautionary note I have is the measure of CH$ emissions given the absence of sampling stations in the tundra and over the shallow waters of Arctic shelves.

Honestly, I'm not trying to be argumentative, but just like radiative forcing, AGGI is calculated from atmospheric concentration measurements, not from emissions.  Because methane is a well-mixed greenhouse gas (unlike, say, tropospheric ozone), whatever methane is generated from the tundra and Arctic shelves and makes its way into the atmosphere will contribute to the globally-averaged atmospheric concentration measurements and thus into AGGI.
Title: Re: Comparison: forcings from CO2, CH4, N2O
Post by: SteveMDFP on August 21, 2018, 01:09:16 PM
I'm not convinced that a real understanding of the mathematical meaning of the term "radiative forcing" is as widespread on ASIF as it ought to be.

For a greenhouse gas, a "radiative forcing" (RF) is simply the change in the Earth's radiation balance when the concentration of that gas changes from some initial value c0 to a different value c1.

Time, per se, is utterly irrelevant to this definition [1].  The times at which c0 and c1 are measured don't matter.  They could be millions of years apart.  Or c0 and c1 could be purely hypothetical, for thought experiments about how much warming would occur under different concentrations of gases.  All that matters are the actual concentrations present in the atmosphere at times c0 and c1.

Mathematically, the forcing from 1765 to present is literally identical to the sum of the forcing from 1765-1766 plus the forcing from 1766-1767 plus the forcing from 1767-1768 plus ... up to the forcing from 2017-2018. 

Ned, thanks for addressing a confusing question.  But what you've described here doesn't match the definitions of radiative forcing to be found at:
https://en.wikipedia.org/wiki/Radiative_forcing
No at:
http://news.mit.edu/2010/explained-radforce-0309

By these definitions, you don't need two points in time, nor do you need any change in any concentration of any GHG. 
Total radiative forcing at any point in time is the imbalance between incoming radiation and  outgoing radiation.  That total imbalance can presumably be broken down by attributable effects of individual gases and particulates.  We have a positive total radiative balance right now, which is ultimately the physical cause of warming across the planet. 
Title: Re: Comparison: forcings from CO2, CH4, N2O
Post by: Ned W on August 21, 2018, 01:22:41 PM
[I see that SteveMDFP has posted another comment while I was writing this ... I'll address that later.]

Discussions about radiative forcing here are often made needlessly complicated when GWP (global warming potential) is kind of mashed into the discussion.  RF and GWP are different quantities and are typically used to answer different kinds of questions.  It's rarely if ever helpful to try to combine them.

RF is a measure of the change in the Earth's radiation balance at time X (with some concentrations of greenhouse gases) relative to some baseline at time Zero (with some other concentrations).  The RF at time X is purely dependent on how many molecules of the gas(es) in question are present in the atmosphere at time X, compared to how many were present at the baseline.

GWP is a measure of how much warming a given quantity of emitted greenhouse gas (e.g., one tonne of methane) will produce, relative to how much warming the same quantity of CO2 would produce, over a specified (long) time period.  It is used primarily by economists, policymakers, etc. to assign costs to anthropogenic emissions of different mixtures of gases, for accounting purposes.

GWP takes into account how long a pulse of a given gas remains in the atmosphere.  RF can also take that into account by calculating the evolution of RF over time, as the emitted pulse of greenhouse gases accumulates and then decays.

For example, consider two hypothetical Earths, both of which have an RF of 3.1 in 2018, relative to a baseline of 1765:

* On Earth 1, that RF comes solely from methane -- concentrations of CO2, N2O, CFCs etc. have not changed at all from 1765 to 2018, only methane has increased, and it's increased exactly enough to produce an RF of 3.1 in 2018.

* One Earth 2, that RF comes solely from CO2 -- concentrations of methane, N2O, etc. are unchanged and only CO2 has increased.  And like on Earth 1, it's created an RF of 3.1 in 2018.

Now, we know that CO2 lasts much longer than methane in the atmosphere.  So while both Earth 1 and Earth 2 have the same RF in 2018, in the following years Earth 1's RF will taper off faster, while Earth 2's RF will take a longer time to decrease.  Eventually (if no more excess emissions are produced) both of them will return to their 1765 concentrations, and have an RF of 0 again.  But that will take a lot longer for Earth 2 than Earth 1.
Title: Re: Comparison: forcings from CO2, CH4, N2O
Post by: Ned W on August 21, 2018, 01:40:36 PM
Ned, thanks for addressing a confusing question.  But what you've described here doesn't match the definitions of radiative forcing to be found at:
https://en.wikipedia.org/wiki/Radiative_forcing
No at:
http://news.mit.edu/2010/explained-radforce-0309

By these definitions, you don't need two points in time, nor do you need any change in any concentration of any GHG. 
Total radiative forcing at any point in time is the imbalance between incoming radiation and  outgoing radiation.  That total imbalance can presumably be broken down by attributable effects of individual gases and particulates.  We have a positive total radiative balance right now, which is ultimately the physical cause of warming across the planet.

Steve, thanks so much for your comment.  You're right that the language used doesn't seem to match, e.g., the opening paragraph of the Wikipedia definition. 

But if you read further, it does match exactly.  For example, on the Wikipedia page, scroll down to "Sample Calculations" and within that, look at "Forcing due to atmospheric gas".  The equation given for RF from CO2 is:

dF = 5.35 * LN(c/c0)

dF is the radiative forcing from CO2.  Look at the remainder of the sentence in your Wikipedia link:

Quote
where C is the CO2 concentration in parts per million by volume and C0 is the reference concentration.

I called them "c1" and "c0" rather than "c" and "c0" but that's just a trivial difference in notation.  The calculation for RF on your Wikipedia page is based on a change in CO2 (or whatever) relative to some "reference" (or "baseline" as I called it) concentration.

See also the quote from IPCC AR4 higher up on the Wikipedia page, which ties together the two seemingly different (but equivalent) definitions of radiative forcing.

Likewise, your link to the MIT page also shows the same thing.  Scroll down on that page to this part:

Quote
For convenience, most researchers choose a “baseline” year before the beginning of world industrialization — usually either 1750 or 1850 — as the zero point, and compute radiative forcing in relation to that base. The IPCC uses 1750 as its base year and it is the changes in the various radiative forcing agents since then that are counted.

So, again, the language used to introduce the concept of RF on that page "feels" different, but when you get down to the nuts and bolts, it turns out to be the same as the definition used elsewhere:  RF is the effect on the Earth's radiation balance of a change in concentration of a greenhouse gas relative to some "baseline" or "reference" concentration.

Hope that helps.
Title: Re: Comparison: forcings from CO2, CH4, N2O
Post by: TeaPotty on August 21, 2018, 02:25:34 PM
Ned, you’re doing a whole lot of talking, and not making any sense.

Is this how you try to win the argument you’ve started, while slandering posters like AbruptSLR?

Stop rambling and try to give a logical explanation for your method.
Title: Re: Comparison: forcings from CO2, CH4, N2O
Post by: Ned W on August 21, 2018, 02:55:18 PM
I've been trying to respond as clearly as possible to specific questions that are raised.  See for example SteveMDFP's post directly above this and my reply. 

If there are specific things that make no sense, point them out and I or someone else can try to address them.

As for ASLR's post and my response, recall that he wrote this:

Quote
This value of 528.2ppm for CO2e for 2017 is well above the 425ppm value assumed by RCP 8.5 (used to force climate models for AR5, see the attached image).

That comparison (528 vs 425 ppmv) is deeply misleading.  It implies that the IPCC's fastest-warming scenario is already underestimating climate forcings by over 100 ppm CO2-equivalent after only a very few years.

Either ASLR understands why those two numbers should not be compared, or he doesn't understand it.  Neither option is very appealing. 

Plus, he and I went over this one year ago (August 2017) and it's not exactly an obscure problem.  See my analogy above:

What ASLR is doing is quite literally equivalent to suggesting that the IPCC has erroneously calculated the area of New York [city] because its number is much smaller than Wikipedia's value for the area of New York [state].   Yeah, they're both called "New York" but the numbers are based on two different definitions of "New York". 

This isn't a minor thing.  People reading ASLR's post who are not familiar with the meaning of "CO2e" will come away from it believing -- incorrectly! -- that the IPCC's scenarios are so wildly wrong that even the fastest-warming one is way, way too low. 

I am used to seeing that kind of thing (in the opposite direction) at WattsUpWithThat.  Let's not put up with it here, please. 
Title: Re: Comparison: forcings from CO2, CH4, N2O
Post by: GoSouthYoungins on August 21, 2018, 03:25:43 PM

I am used to seeing that kind of thing (in the opposite direction) at WattsUpWithThat.  Let's not put up with it here, please.

Babble babble babble babble, babble babble babble babble. Ya, he was comparing different things. But I think you are concentrating on that to hide that you don't understand what you post so prolifically about in the thread you started.  If GWP100 and GWP20 are able to be calculated, why not GWP1?  Why not explain with some math so we all understand?!?
Title: Re: Comparison: forcings from CO2, CH4, N2O
Post by: Ned W on August 21, 2018, 03:36:48 PM
If GWP100 and GWP20 are able to be calculated, why not GWP1?  Why not explain with some math so we all understand?!?

You asked that question in this post (https://forum.arctic-sea-ice.net/index.php/topic,2383.msg168510.html#msg168510):

Quote from: GoSouthYoungins
So whats CH4's GWP1? It's the question I've asked a dozen times in various threads, and no one is interested...why?

I replied in this post (https://forum.arctic-sea-ice.net/index.php/topic,2383.msg168514.html#msg168514):

Quote from: Ned W
Probably because it ignores all the warming that happens after that first year is over.  The entire point of GWP is to account for the integrated warming produced by a molecule of gas X over a long period of time.

You then replied in this post:

Quote from: GoSouthYoungins
If you are calculating how much warming happens in a year, shouldn't that inherently ignore all the warming that will happen after that, and solely concentrate on that year?

And I replied with this explanation (https://forum.arctic-sea-ice.net/index.php/topic,2383.msg168520.html#msg168520), complete with numbers and tables:

Quote from: Ned W
As a simple example [... simple example omitted ...]

So, to answer your question: Let's say you are interested in the warming that occurs in year 3.  You are correct that you don't need to know about warming that occurs a year later (year 4).  But you do need to know about warming caused by molecules emitted a year earlier (year 2) because in the case of gas Y, molecules emitted during year 2 are still producing warming during year 3.

As far as I can see, you never acknowledged or responded in any way to that.  Now you're insistently demanding that I answer some other questions.  Meanwhile I'm getting flack from people for posting too much already. 
Title: Re: Comparison: forcings from CO2, CH4, N2O
Post by: Ned W on August 21, 2018, 04:22:09 PM
To (hopefully) halt the increasing acrimony and get back to where this thread started, here's a graph similar to the one in the second post, but for rolling 30-year windows:

(https://i.imgur.com/lFdIZSi.png)

So each point along one of those lines is the radiative forcing at a given year (the X axis) relative to a baseline 30 years earlier.  In other words, it's the magnitude of the radiative forcing from each gas over the previous 30 years.

During the 30-year periods ending in the 1950s and 1960s (i.e., encompassing data from the 1920s/30s to the 1950s/60s) the forcing from methane was only slightly lower than that from CO2.  But that changed in later years, and the most recent 30-year period (far right end of chart) has the biggest gap between CO2 forcing and CH4 forcing.

That said, methane concentrations did resume rising a decade ago, so the orange line will start to turn back up at some point. 

-----------------

The data are from CMIP5 (prior to 2005) and from NOAA (post 2005).  The CMIP5 estimates for CH4 concentration during the period of overlap (1984-2005) are offset relative to the NOAA series, so I shifted them by ~20 ppb for consistency.
Title: Re: Comparison: forcings from CO2, CH4, N2O
Post by: AbruptSLR on August 21, 2018, 06:03:46 PM
In the linked thread entitle: "Radiative forcing and CO2eq", I explain in Reply #38 that what people really care about is effective radiative forcing, ERF, rather than radiative forcing, RF; while in Replies #45 & #46  I explain that AR5 had a number of shortcomings about near-term climate forcers, NTCFs (including methane and aerosols), that AerChemMIP is working to address:

https://forum.arctic-sea-ice.net/index.php/topic,2158.0.html#lastPost

From Reply #38:

"What people really care about is how big will the climate impacts be and how fast will they occur.  Thus people are really interested in effective radiative forcing, ERF, rather than RF (see the following linked lecture visuals & attached image) due to the combination of forcings and feedbacks.

Title: "Forcing and feedbacks", from Climate Dynamics (Summer Semester 2017) by J. Mulmenstadt

https://home.uni-leipzig.de/~jmuelmen/lehre/cd/cd-2017/lec11.pdf

The link makes it clear that considering the fast response from CO₂ is relatively straight forward, but the impacts from slow response feedbacks, particularly from the ocean (note that OHC is higher than AR5 assumed, as the oceans have been absorbing extra heat since 1750) and ENSO can rapidly increase effective values of ECS up to the range of 4 to 5C.  If so then the Zhang et al (2016) values (which include feedbacks) are not 'outliers' but rather are an indication that the effective ECS this century is higher than other researchers are assuming.  Furthermore, the attached image illustrates how ERF can be determined but due to uncertainties accurate estimates of ERF will take decades, and by that time we may have crossed several tipping points if AR5 is erring on the side of least drama."

From Reply #45:

Obviously, the issues raised in this thread do not represent 'settled science' as indicated by the linked reference about CMIP6's efforts to better quantify these effects:

Collins et al (2017), "AerChemMIP: quantifying the effects of chemistry and aerosols in CMIP6", Geosci. Model Dev., 10, 585–607, doi:10.5194/gmd-10-585-2017

https://www.geosci-model-dev.net/10/585/2017/gmd-10-585-2017.pdf

Abstract: "Abstract. The Aerosol Chemistry Model Intercomparison Project (AerChemMIP) is endorsed by the Coupled-Model Intercomparison Project 6 (CMIP6) and is designed to quantify the climate and air quality impacts of aerosols and chemically reactive gases. These are specifically near-term climate forcers (NTCFs: methane, tropospheric ozone and aerosols, and their precursors), nitrous oxide and ozone depleting halocarbons. The aim of AerChemMIP is to answer four scientific questions.

1. How have anthropogenic emissions contributed to global radiative forcing and affected regional climate over the historical period?

2. How might future policies (on climate, air quality and land use) affect the abundances of NTCFs and their climate impacts?

3. How do uncertainties in historical NTCF emissions affect radiative forcing estimates?

4. How important are climate feedbacks to natural NTCF emissions, atmospheric composition, and radiative effects?

These questions will be addressed through targeted simulations with CMIP6 climate models that include an interactive representation of tropospheric aerosols and atmospheric chemistry. These simulations build on the CMIP6 Diagnostic, Evaluation and Characterization of Klima (DECK) experiments, the CMIP6 historical simulations, and future projections performed elsewhere in CMIP6, allowing the contributions from aerosols and/or chemistry to be quantified.  Specific diagnostics are requested as part of the CMIP6 data request to highlight the chemical composition of the atmosphere, to evaluate the performance of the models, and to understand differences in behaviour between them."

From Reply #46:

To reiterate the point of my last post, the linked reference concludes that there is a lot of uncertainty associated with model projections of the impacts of aerosols and chemically reactive gases:

Heyn, I., K. Block, J. Mülmenstädt, E. Gryspeerdt, P. Kühne, M. Salzmann, and J. Quaas (2017), Assessment of simulated aerosol effective radiative forcings in the terrestrial spectrum, Geophys. Res. Lett., 44, doi:10.1002/2016GL071975.

https://spiral.imperial.ac.uk/bitstream/10044/1/43885/7/Heyn_et_al-2017-Geophysical_Research_Letters.pdf

Extract: "The analysis in this paper relies on global climate models. Beyond climate model results, very little is known quantitatively about the global forcing due to the reaction of ice-phase, mixed-phase, and deep convective clouds to aerosol perturbations. A truly realistic estimate, or even just reliable uncertainty interval, thus requires substantial further research, especially for effects in the terrestrial spectrum. Observational estimates are urgently needed. The current state of the art, however, suggests that the effective forcing in the terrestrial spectrum is either small, or, for models where it is large, is accompanied by a large negative effective forcing in the solar spectrum."
Title: Re: Comparison: forcings from CO2, CH4, N2O
Post by: GoSouthYoungins on August 21, 2018, 07:13:30 PM

As far as I can see, you never acknowledged or responded in any way to that.  Now you're insistently demanding that I answer some other questions.  Meanwhile I'm getting flack from people for posting too much already.

Sorry if I was too harsh before. My question has always been the same: What is the CH4 multiplier (or CO2e) for a time less than or equal to its atmospheric lifespan?  GWP1 or GWP10 would work fine. Any time horizon longer than its lifespan will downplay its short term effect.

GPW100  =  30
GWP20    =  85
GWP10    =  100-300???

Title: Re: Comparison: forcings from CO2, CH4, N2O
Post by: SteveMDFP on August 21, 2018, 07:29:03 PM

Likewise, your link to the MIT page also shows the same thing.  Scroll down on that page to this part:

Quote
For convenience, most researchers choose a “baseline” year before the beginning of world industrialization — usually either 1750 or 1850 — as the zero point, and compute radiative forcing in relation to that base. The IPCC uses 1750 as its base year and it is the changes in the various radiative forcing agents since then that are counted.

So, again, the language used to introduce the concept of RF on that page "feels" different, but when you get down to the nuts and bolts, it turns out to be the same as the definition used elsewhere:  RF is the effect on the Earth's radiation balance of a change in concentration of a greenhouse gas relative to some "baseline" or "reference" concentration.

Hope that helps.

Thanks Ned.  I see that you're correct.  If one assumes that the climate was in thermodynamic equilibrium in 1750 or 1850 (quite reasonable as a first approximation, I think), then the radiative forcing at those moments would be zero.  In this approximation, the two wordings of the definition would be synonymous.  The positive radiative forcing today is (approximately) the true heat imbalance resulting in continued warming of the globe.

Now, that pesky methane question.  Appropriate answers depend on precise questions and precise definitions.  I think ASLR is correct that, for example, real people care about projected effects under reasonable scenarios, and different answers are true from some of the precise, technical answers.

If we project zero rise or fall in methane concentrations over the next century (a very conservative assumption, I think) then for any meaningful answer to what methane will do to the climate, the lifetime of a methane molecule becomes irrelevant.  Each oxidized molecule is replaced.

The GWP50 for methane then becomes severely underestimated for assessing what that specific methane concentration will do to the climate.
Title: Re: Comparison: forcings from CO2, CH4, N2O
Post by: AbruptSLR on August 21, 2018, 07:29:15 PM
The attached image presented by the chairman of Chapter 8 of AR5, shows the time evolution of the ERF by agent, and which shows the relative importance of CO₂ compared to other well mixed GHGs:

Title: "Radiative Forcing in the AR5" presented by Drew Shindell

http://climate.envsci.rutgers.edu/climdyn2013/IPCC/IPCC_WGI12-RadiativeForcing.pdf

Title: Re: Comparison: forcings from CO2, CH4, N2O
Post by: wili on August 21, 2018, 07:41:58 PM
This article may be relevant to the current discussion (though it is somewhat old now--relevant updates on the subject would be most welcome, especially with links!):

Quote
It is shown that if global methane emissions were to increase by factors of 2.5 and 5.2 above current emissions, the indirect contributions to RF would be about 250% and 400%, respectively, of the RF that can be attributed to directly emitted methane alone.

Assuming several hypothetical scenarios of CH4 release associated with permafrost thaw, shallow marine hydrate degassing, and submarine landslides, we find a strong positive feedback on RF through atmospheric chemistry. In particular, the impact of CH4 is enhanced through increase of its lifetime, and of atmospheric abundances of ozone, stratospheric water vapor, and CO2
as a result of atmospheric chemical processes

https://darchive.mblwhoilibrary.org/bitstream/handle/1912/4553/2010GB003845.pdf?sequence=1

See also (with similar caveats):

Shindell, D.T., G. Faluvegi, D.M. Koch, G.A. Schmidt, N. Unger, and S.E. Bauer, 2009: Improved attribution of climate forcing to emissions. Science, 326, 716-718, doi:10.1126/science.1174760.

(from the note under figure 2):

“Our calculations for the shorter 20-year GWP, including aerosol responses, yield values of 79 and 105 for methane”

(the latter number is for full accounting of both direct and indirect aerosol effect. Bar chart shows 33 for 100 year value.)

http://www.see.ed.ac.uk/~shs/Climate%20change/Data%20sources/Shindell%20methane.pdf
Title: Re: Comparison: forcings from CO2, CH4, N2O
Post by: Ned W on August 21, 2018, 08:11:02 PM
Quote from: AbruptSLR
what people really care about is effective radiative forcing, ERF, rather than radiative forcing, RF

For the subjects of this thread (CO2, CH4, and N2O) the difference between ERF and stratospherically adjusted RF is extremely small (e.g., for CO2, ERF is only 2% smaller than RF).  See page 667 of AR5, starting with "In many cases, however, ERF and RF are nearly equal...." 

Thus, since the difference is fairly trivial, and since it's very easy to calculate stratospherically adjusted RF, and very hard to calculate ERF, in this thread and elsewhere I encourage people to basically ignore ERFs for the well-mixed greenhouse gases and just use RFs. 

Anyone can calculate the RF for CO2, CH4, or N2O and do various thought experiments, e.g. see for themselves what effect adding 100 ppb of methane would have done in 1750 vs today, or whatever. 
Title: Re: Comparison: forcings from CO2, CH4, N2O
Post by: AbruptSLR on August 21, 2018, 09:43:51 PM
AR5 Chapter 8 does a reasonably good job of calculating current ERF (see linked pdf) it is not hard for most people to see per Figure 8.15, the solid bars are for ERF and the solid uncertainty lines are also for ERF.  Thus if one take the high end of uncertainty for Other WMGHGs its ERF in 2011 may be close to equaling the low uncertainty end of the ERF for carbon dioxide.

Also, per Figure 8.32 that on a ten year horizon that for the current anthropogenic GHG emissions that the global warming potential of methane exceeds that of that for carbon dioxide.  So if the combine natural and anthropogenic methane emissions keep pace with the combined natural and anthropogenic carbon dioxide emissions then we could all be in trouble (see Isaksen et al. 2011).  Also, I note that what is difficult to calculate is the true value of ECS by say 2100 (the ACME model projects this value to be about 5.2C), as ECS increases with continued global warming:

Title: "Chapter 8:  Anthropogenic and Natural Radiative Forcing"

https://www.ipcc.ch/pdf/assessment-report/ar5/wg1/WG1AR5_Chapter08_FINAL.pdf

&

Isaksen, I. S. A., Gauss M., Myhre, G., Walter Anthony, K. M.  and Ruppel, C.,  (2011), "Strong atmospheric chemistry feedback to climate warming from Arctic methane emissions", Global Biogeochem. Cycles, 25, GB2002, doi:10.1029/2010GB003845.

http://onlinelibrary.wiley.com/doi/10.1029/2010GB003845/abstract

Title: Re: Comparison: forcings from CO2, CH4, N2O
Post by: AbruptSLR on August 21, 2018, 09:50:27 PM
Regarding my last post, the DOE has recently released computer code & preliminary results from ACME (Accelerated Climate Model for Energy) while the DOE has renamed the program E3SM (Energy Exascale Earth System Model), and this world's most sophisticated climate model projects that ECS for the rest of this century will be about 5.2C (& this relatively high value is likely attributable to the state-of-the-art way that ACME/E3SM models aerosols and cloud feedback mechanisms).

While some consensus scientists (like Bjorn Stevens) have said that it is difficult to determine whether the ACME findings are any more relevant than other models in the CMIP6 program; I believe that these findings from the world's most advanced ESM warrant the adoptions of the Precautionary Principle, particularly as the ACME results only partially address Hansen's ice-climate feedback mechanism:

Title: "DOE’s maverick climate model is about to get its first test"
doi:10.1126/science.aau0578

http://www.sciencemag.org/news/2018/05/does-maverick-climate-model-about-get-its-first-test

Extract: "In 2017, after President Donald Trump took office and pulled the nation out of the Paris climate accords, DOE dropped "climate" from the project name. The new name, the Energy Exascale Earth System Model (E3SM), better reflects the model's focus on the entire Earth system, says project leader David Bader of Lawrence Livermore National Laboratory in California.
..
One preliminary result, on the climate's sensitivity to carbon dioxide (CO2), will "raise some eyebrows," Bader says. Most models estimate that, for a doubling of CO2 above preindustrial levels, average global temperatures will rise between 1.5°C and 4.5°C. The E3SM predicts a strikingly high rise of 5.2°C, which Leung suspects is due to the way the model handles aerosols and clouds. And like many models, the E3SM produces two bands of rainfall in the tropics, rather than the one seen in nature near the equator.

The first test of the E3SM will be its performance in CMIP6. Nearly three dozen modeling groups, including newcomers from South Korea, India, Brazil, and South Africa, are expected to submit results to the intercomparison between now and 2020."

See also:

https://gcn.com/articles/2018/04/26/e3sm-earth-model.aspx

&

https://www.llnl.gov/news/new-exascale-system-earth-simulation

See also:

Title: "SimEarth"

https://phys.org/news/2018-05-simearth.html

Extract: ""With this new system, we'll be able to more realistically simulate the present, which gives us more confidence to simulate the future," says David Bader, computational scientist at Lawrence Livermore National Laboratory and overall E3SM project lead."
Title: Re: Comparison: forcings from CO2, CH4, N2O
Post by: AbruptSLR on August 21, 2018, 11:02:39 PM
The attached image from von Deimling et al. (2015) shows how much methane could be emitted from thermokarst activity by 2050 if we continue to follow a BAU pathway:

Schneider von Deimling, T., Grosse, G., Strauss, J., Schirrmeister, L., Morgenstern, A., Schaphoff, S., Meinshausen, M., and Boike, J.: Observation-based modelling of permafrost carbon fluxes with accounting for deep carbon deposits and thermokarst activity, Biogeosciences, 12, 3469-3488, doi:10.5194/bg-12-3469-2015, 2015.

http://www.biogeosciences.net/12/3469/2015/bg-12-3469-2015.html

See also:

Katey Walter Anthony, Thomas Schneider von Deimling, Ingmar Nitze, Steve Frolking, Abraham Emond, Ronald Daanen, Peter Anthony, Prajna Lindgren, Benjamin Jones, Guido Grosse. 21st-century modeled permafrost carbon emissions accelerated by abrupt thaw beneath lakes. Nature Communications, 2018; 9 (1) DOI: 10.1038/s41467-018-05738-9

http://www.nature.com/articles/s41467-018-05738-9

Extract: "These finding demonstrate the need to incorporate abrupt thaw processes in earth system models for more comprehensive projection of the PCF this century."

See also:

Title: "'Abrupt thaw' of permafrost beneath lakes could significantly affect climate change models"

https://www.sciencedaily.com/releases/2018/08/180816143035.htm
Title: Re: Comparison: forcings from CO2, CH4, N2O
Post by: Ned W on August 21, 2018, 11:09:53 PM
The attached image from von Deimling et al. (2015) shows how much methane could be emitted from thermokarst activity by 2050 if we continue to follow a BAU pathway:

[snip]

See also:

Katey Walter Anthony, Thomas Schneider von Deimling, Ingmar Nitze, Steve Frolking, Abraham Emond, Ronald Daanen, Peter Anthony, Prajna Lindgren, Benjamin Jones, Guido Grosse. 21st-century modeled permafrost carbon emissions accelerated by abrupt thaw beneath lakes. Nature Communications, 2018; 9 (1) DOI: 10.1038/s41467-018-05738-9

http://www.nature.com/articles/s41467-018-05738-9

[snip]

See also:

Title: "'Abrupt thaw' of permafrost beneath lakes could significantly affect climate change models"

https://www.sciencedaily.com/releases/2018/08/180816143035.htm

FYI, all three of those were discussed on the previous page of this thread.
Title: Re: Comparison: forcings from CO2, CH4, N2O
Post by: AbruptSLR on August 21, 2018, 11:31:33 PM
FYI, all three of those were discussed on the previous page of this thread.

Some things bear repeating.
Title: Re: Comparison: forcings from CO2, CH4, N2O
Post by: TeaPotty on August 22, 2018, 12:21:39 AM
Ned, you havent presented a good argument for the reason you started this thread. I don’t think the math is on your side, so I’m not sure how you aim to prove that CH4 isn’t important or significant in forcing.

You seem stuck on RF vs ERF, favoring one side bc the numbers fit your reality. As far back as I can remember, ERF was the better measurement. Besides that, you just ignore all methane feedbacks. Is there a point to continuing this discussion?
Title: Re: Comparison: forcings from CO2, CH4, N2O
Post by: GoSouthYoungins on August 22, 2018, 12:46:08 AM
How is it that NO ONE can give a reasonable estimate for the GWP10 of CH4? Does anyone actually have any idea what they are talking about, or is this just a much people repeating tidbits from scientific papers to make themselves feel smart?
Title: Re: Comparison: forcings from CO2, CH4, N2O
Post by: SteveMDFP on August 22, 2018, 01:19:44 AM
How is it that NO ONE can give a reasonable estimate for the GWP10 of CH4? Does anyone actually have any idea what they are talking about, or is this just a much people repeating tidbits from scientific papers to make themselves feel smart?

No need to cast aspersions.  This source reports a GWP-20 (20 years) of 108:

A bridge to nowhere: methane emissions and thegreenhouse gas footprint of natural gas
https://onlinelibrary.wiley.com/doi/epdf/10.1002/ese3.35 (https://onlinelibrary.wiley.com/doi/epdf/10.1002/ese3.35)

Cited references should give GWP for shorter intervals.  I may dig into them.
Title: Re: Comparison: forcings from CO2, CH4, N2O
Post by: AbruptSLR on August 22, 2018, 01:43:50 AM
How is it that NO ONE can give a reasonable estimate for the GWP10 of CH4? Does anyone actually have any idea what they are talking about, or is this just a much people repeating tidbits from scientific papers to make themselves feel smart?

Sam Carana is a controversial figure, but he says that he produced the first image using Shindell et al. (2009), which give an average GWP10 value for methane with aerosol feedback of 130.

As Sam is controversial and as there is an uncertainty range, which Shindell et al. (2009) cited as from 79 to 105 for GWP20, when including the influence of aerosols; which has an average value of 92.

Drew T. Shindell, Greg Faluvegi, Dorothy M. Koch, Gavin A. Schmidt, Nadine Unger & Susanne E. Bauer (Oct 30, 2009)"Improved Attribution of Climate Forcing to Emissions", Science  Vol. 326, Issue 5953, pp. 716-718, DOI: 10.1126/science.1174760

http://www.energyjustice.net/files/naturalgas/2009shindell.pdf

Extract: "… Our calculations for the shorter 20-year GWP, including aerosol responses, yield
values of 79 and 105 for methane …"

Table 8.7 of AR5 says that GWP20 for methane without climate-carbon feedback (but without aerosol feedback) is 84.  While per Figures 8.29 & 8.30 (and Figure 8.32) of AR5 (see the last three images respectively), GWP10 (but without aerosol feedback) is about 110.  Thus if one were to take a ratio of Shindell et al. (2009)'s average GWP20 of 92 with AR5's value of 84, would indicate a mean GWP10 for methane including aerosols of about 120; however, to include climate-carbon feedback would increase this mean value to over 121 +/- 17; which is reasonably close to Sam Carana's value.

Title: "Chapter 8:  Anthropogenic and Natural Radiative Forcing"

https://www.ipcc.ch/pdf/assessment-report/ar5/wg1/WG1AR5_Chapter08_FINAL.pdf
Title: Re: Comparison: forcings from CO2, CH4, N2O
Post by: GoSouthYoungins on August 22, 2018, 02:13:37 AM
Thank you.

CO2 change since pre industrial 120 ppm.

CH4 change since pre industrial 1.2 ppm. 120 times the forcing = 144 pp CO2e.

Methane forcing greater than CO2. If anyone can tell me why that's wrong, please do. From my perspective, methane warming is the opposite of tiny relative to CO2, it is LARGER, the main contributor to warming.



Title: Re: Comparison: forcings from CO2, CH4, N2O
Post by: AbruptSLR on August 22, 2018, 02:16:09 AM
... This source reports a GWP-20 (20 years) of 108:

A bridge to nowhere: methane emissions and thegreenhouse gas footprint of natural gas
https://onlinelibrary.wiley.com/doi/epdf/10.1002/ese3.35 (https://onlinelibrary.wiley.com/doi/epdf/10.1002/ese3.35)

Cited references should give GWP for shorter intervals.  I may dig into them.

SteveMDFP,

Per the extract below Howarth (2014) cites a GWP10 for methane of 108 (which he gets from AR5 Chapter 8, see also Table 2 attached which says that Shindell et al. gives a GWP20 value of 105 instead of 86); however, I do not believe that AR5 Chapter 8 assigns the aerosol feedback to this value:

Robert W. Howarth (2014), "A bridge to nowhere: methane emissions and the greenhouse gas footprint of natural gas", Energy Science & Engineering, doi: 10.1002/ese3.35

https://onlinelibrary.wiley.com/doi/epdf/10.1002/ese3.35

Extract: "The most recent synthesis report from the IPCC in 2013 on the physical science basis of global warming highlights the role of methane in global warming at multiple timescales, using GWP values for 10 years in addition to 20 and 100 years (GWP of 108, 86, and 34,respectively) in their analysis"
Title: Re: Comparison: forcings from CO2, CH4, N2O
Post by: AbruptSLR on August 22, 2018, 02:20:37 AM
Methane forcing greater than CO2.

AR5 Chapter 8 Figure 8.32 says that over a 10-year duration your statement is correct.
Title: Re: Comparison: forcings from CO2, CH4, N2O
Post by: SteveMDFP on August 22, 2018, 02:29:24 AM

Per the extract below Howarth (2014) cites a GWP10 for methane of 108 

My error!  Careless reading on my part.
Glad you found the article to be worthwhile to read and cite.
Title: Re: Comparison: forcings from CO2, CH4, N2O
Post by: Ned W on August 22, 2018, 03:33:36 AM
Thank you.

CO2 change since pre industrial 120 ppm.

CH4 change since pre industrial 1.2 ppm. 120 times the forcing = 144 pp CO2e.

Methane forcing greater than CO2. If anyone can tell me why that's wrong, please do. From my perspective, methane warming is the opposite of tiny relative to CO2, it is LARGER, the main contributor to warming.

I'm trying to figure out some way of saying this that won't sound insulting, because that's not my intent at all.  But your post is all so thoroughly confused that one hardly knows where to begin in untangling it.  You are mixing up the concepts of GWP, RF, and concentration, and unsurprisingly getting an answer that is completely wrong.

No, methane's forcing since pre-industrial is not "greater than CO2". WTF are you thinking?  You've just discovered that every single geochemist and climate scientist on the planet is wrong? 

Title: Re: Comparison: forcings from CO2, CH4, N2O
Post by: Ned W on August 22, 2018, 04:10:45 AM
Ned, you havent presented a good argument for the reason you started this thread.

I started this thread because I wanted to play around with some comparisons of the radiative forcings from CO2, CH4, and N2O -- as it says in the title.

Also, I think that some people here have honest but mistaken ideas about how important methane is now (and in the recent past/immediate future) in a relative sense, e.g. when compared to the forcing from CO2. 

Quote
I don’t think the math is on your side, so I’m not sure how you aim to prove that CH4 isn’t important or significant in forcing.

Why do you not think the math is on my side? 

I've calculated the effects of actual, measured changes in CH4 and CO2 in recent years, in terms of radiative forcing, meaning how much the increased concentration of each gas alters the planet's energy balance.

The methods I've used are based on Etimnan et al. 2016, a widely accepted updating of the standard models for radiative forcing endorsed by the IPCC and by climate scientists worldwide.

If you think there's a problem with the math, have you tried doing it yourself?  What did you get as a result?

Quote
You seem stuck on RF vs ERF, favoring one side bc the numbers fit your reality. As far back as I can remember, ERF was the better measurement. Besides that, you just ignore all methane feedbacks.

That is baffling, because from where I sit it's ASLR, not me, who is hung up on RF vs ERF.  He's the one who keeps bringing it up, not me.  My only comment on that has been to point out that for these three gases, there is almost no difference between RF and ERF.  The two are almost identical.  So it doesn't matter which one you use.

How is that "being stuck on RF vs ERF"?

As for the final point, this thread is about forcing, not feedbacks.  But having said that, methane (and CO2, and N2O) feedbacks that are operating now or in the past will of course have contributed to te observed concentrations of the three gases, and thus will be fully accounted for in my calculations.  Do you understand this point?

It's true that for the purposes of this thread I'm not thinking much about new feedbacks that might appear in the future.  That's a different topic, as far as I'm concerned.  I'm focused on actual observational data here.

Quote
Is there a point to continuing this discussion?

I don't know.  To be honest, I'm beginning to have second thoughts about that.   
Title: Re: Comparison: forcings from CO2, CH4, N2O
Post by: Richard Rathbone on August 22, 2018, 04:20:49 AM
The purpose of GWP  is to compare the harm done by emissions of different substances. The period of time to use, is the period over which you are concerned about harm being done. Using GWP1, is appropriate when you don't care about what happens after 2019, GWP10 when you don't care about what happens after 2028, GWP50 when you don't care about what happens after 2068.

Its a concept to use when comparing emissions, not concentrations.

GWP is for answering questions like "How does the damage done by methane leaking from a pipeline compare with the damage from CO2 if it was burnt?"

If you choose to ignore almost all of the damage done by CO2, then you can make CH4 look bad compared to it. Thats what a short duration GWP does.
Title: Re: Comparison: forcings from CO2, CH4, N2O
Post by: jai mitchell on August 22, 2018, 05:37:24 AM
If you choose to ignore almost all of the damage done by CO2, then you can make CH4 look bad compared to it. Thats what a short duration GWP does.

I disagree,

If you want to know what current human activity (and carbon cycle feedbacks) will do in the near term, it is very appropriate to use GWP20, the use of GWP100 is a terrible oversight with regard to policymaking.
Title: Re: Comparison: forcings from CO2, CH4, N2O
Post by: GoSouthYoungins on August 22, 2018, 05:49:33 AM
Thank you.

CO2 change since pre industrial 120 ppm.

CH4 change since pre industrial 1.2 ppm. 120 times the forcing = 144 pp CO2e.

Methane forcing greater than CO2. If anyone can tell me why that's wrong, please do. From my perspective, methane warming is the opposite of tiny relative to CO2, it is LARGER, the main contributor to warming.

I'm trying to figure out some way of saying this that won't sound insulting, because that's not my intent at all.  But your post is all so thoroughly confused that one hardly knows where to begin in untangling it.  You are mixing up the concepts of GWP, RF, and concentration, and unsurprisingly getting an answer that is completely wrong.

No, methane's forcing since pre-industrial is not "greater than CO2". WTF are you thinking?  You've just discovered that every single geochemist and climate scientist on the planet is wrong?

I'm not offended. I don't really care about this like that. I just want to understand. But I can't get a simple answer as to why my math is wrong. And I give absolutely no deference to established climate science and geochemists. I have never come across something that is so complex and mysterious that I can't wrap my mind around the general forces interactions. Tell me why I'm wrong. Tell me what right looks like.
Title: Re: Comparison: forcings from CO2, CH4, N2O
Post by: AbruptSLR on August 22, 2018, 05:50:17 AM
The purpose of GWP  is to compare the harm done by emissions of different substances. The period of time to use, is the period over which you are concerned about harm being done. Using GWP1, is appropriate when you don't care about what happens after 2019, GWP10 when you don't care about what happens after 2028, GWP50 when you don't care about what happens after 2068.

Its a concept to use when comparing emissions, not concentrations.

GWP is for answering questions like "How does the damage done by methane leaking from a pipeline compare with the damage from CO2 if it was burnt?"

If you choose to ignore almost all of the damage done by CO2, then you can make CH4 look bad compared to it. Thats what a short duration GWP does.
I fully concur with all of your points.  That said, decisionmakers think that they can control their WMGHG emissions over the coming decades, but I doubt that they can, and high anthropogenic WMGHG emissions for several more decades can/will trigger a cascade of tripping points for various natural methane emissions.
Title: Re: Comparison: forcings from CO2, CH4, N2O
Post by: AbruptSLR on August 22, 2018, 05:56:37 AM
I'm not offended. I don't really care about this like that. I just want to understand. But I can't get a simple answer as to why my math is wrong. And I give absolutely no deference to established climate science and geochemists. I have never come across something that is so complex and mysterious that I can't wrap my mind around the general forces interactions. Tell me why I'm wrong. Tell me what right looks like.

You need to limit your period of consideration to a very recent ten year time period like from 2002 to 2012 (again see Figure 8.32 from AR5, that I provided twice, see my Replies #49 & 57).
Title: Re: Comparison: forcings from CO2, CH4, N2O
Post by: GoSouthYoungins on August 22, 2018, 06:01:14 AM
I'm not offended. I don't really care about this like that. I just want to understand. But I can't get a simple answer as to why my math is wrong. And I give absolutely no deference to established climate science and geochemists. I have never come across something that is so complex and mysterious that I can't wrap my mind around the general forces interactions. Tell me why I'm wrong. Tell me what right looks like.

You need to limit your period of consideration to a very recent ten year time period like from 2002 to 2012 (again see Figure 8.32 from AR5, that I provided twice, see my Replies #49 & 57).

Why? I am primarily concerned with the warming that will be cause during 2018 vs 1750 broken down by gas. I have seen nothing to convince me that CO2 will have a larger impact the CH4. So yes, Ned, if climate scientist and geochemists disagree with that, I think they are wrong.
Title: Re: Comparison: forcings from CO2, CH4, N2O
Post by: AbruptSLR on August 22, 2018, 06:03:41 AM
If you choose to ignore almost all of the damage done by CO2, then you can make CH4 look bad compared to it. Thats what a short duration GWP does.

I disagree,

If you want to know what current human activity (and carbon cycle feedbacks) will do in the near term, it is very appropriate to use GWP20, the use of GWP100 is a terrible oversight with regard to policymaking.


The ACME results that indicate a ECS of 5.2C by 2100 do not make use of any GWP value at all, so if policymakers would just pay attention to the most advanced ESM projections we could start making some progress.
Title: Re: Comparison: forcings from CO2, CH4, N2O
Post by: AbruptSLR on August 22, 2018, 06:10:58 AM

You need to limit your period of consideration to a very recent ten year time period like from 2002 to 2012 (again see Figure 8.32 from AR5, that I provided twice, see my Replies #49 & 57).
[/quote]

Why? I am primarily concerned with the warming that will be cause during 2018 vs 1750 broken down by gas. I have seen nothing to convince me that CO2 will have a larger impact the CH4. So yes, Ned, if climate scientist and geochemists disagree with that, I think they are wrong.
[/quote]

If you bother to read Chapter 8 of AR5, it clearly explains that the lifespan of methane in the atmosphere is much shorter than that of carbon dioxide.  Thus for the same emission rates the carbon dioxide will buildup to much higher concentrations than would the methane.  But since 1750, the emission rates of methane have been much lower than for carbon dioxide.  Thus it is absolutely clear that since 1750 carbon dioxide has resulted in much more radiative forcing (effective or otherwise) than methane.
Title: Re: Comparison: forcings from CO2, CH4, N2O
Post by: GoSouthYoungins on August 22, 2018, 06:21:00 AM

If you bother to read Chapter 8 of AR5, it clearly explains that the lifespan of methane in the atmosphere is much shorter than that of carbon dioxide.  Thus for the same emission rates the carbon dioxide will buildup to much higher concentrations than would the methane.  But since 1750, the emission rates of methane have been much lower than for carbon dioxide.  Thus it is absolutely clear that since 1750 carbon dioxide has resulted in much more radiative forcing (effective or otherwise) than methane.

I'm talking about how much CH4 and CO2 warmed the atmosphere in 1750, and how much they each will warm the atmosphere in 2018, and then 2018 values minus 1750 values. I'm quite sure this is relevant, and I'm quite sure the value for CH4 has increased more than CO2. But nobody ever puts it in these terms. Which leads many to the idea that the methane has a tiny impact.
Title: Re: Comparison: forcings from CO2, CH4, N2O
Post by: Ned W on August 22, 2018, 12:37:17 PM
I'm talking about how much CH4 and CO2 warmed the atmosphere in 1750, and how much they each will warm the atmosphere in 2018, and then 2018 values minus 1750 values. I'm quite sure this is relevant, and I'm quite sure the value for CH4 has increased more than CO2. But nobody ever puts it in these terms. Which leads many to the idea that the methane has a tiny impact.

Here you go. This should be exactly what you are asking for. 

First, the equations:

(https://i.imgur.com/ETqIvzS.png)

1750 concentrations of gases
CO2 = 280 ppm
CH4   = 722 ppb
N2O = 270 ppm

2017 concentrations
CO2 = 405
CH4   = 1849.7
N2O = 329.7

Radiative forcing, 1750 to 2017
CO2 = 1.99 Watts per square meter
CH4 = 0.63 Watts per square meter

CO2 to CH4 ratio: 3.17

You need to limit your period of consideration to a very recent ten year time period like from 2002 to 2012.

Here is your 2002-2012 period:

2002 concentrations of gases
CO2 = 372.4   
CH4   = 1772.5   
N2O = 317

2012 concentrations
CO2 = 392.5   
CH4   = 1808.2   
N2O = 325

Radiative forcing, 2002 to 2012
CO2 = 0.28 Watts per square meter
CH4 = 0.02 Watts per square meter

CO2 to CH4 ratio: 17.39

And here is the most recent ten-year period (2007-2017):

2007 concentrations of gases
CO2 = 384.8      
CH4   = 1786.9
N2O = 321.6

2017 concentrations: see above

Radiative forcing, 2007 to 2017
CO2 = 0.27 Watts per square meter
CH4 = 0.03 Watts per square meter

CO2 to CH4 ratio: 9.71

Sources:

1750 concentrations:
http://cdiac.ess-dive.lbl.gov/pns/current_ghg.html

Recent concentrations:
https://www.esrl.noaa.gov/gmd/aggi/NOAA_MoleFractions_2018.csv

Methods:
https://agupubs.onlinelibrary.wiley.com/doi/epdf/10.1002/2016GL071930
Title: Re: Comparison: forcings from CO2, CH4, N2O
Post by: AbruptSLR on August 22, 2018, 05:01:35 PM

You need to limit your period of consideration to a very recent ten year time period like from 2002 to 2012.

Here is your 2002-2012 period:

2002 concentrations of gases
CO2 = 372.4   
CH4   = 1772.5   
N2O = 317

2012 concentrations
CO2 = 392.5   
CH4   = 1808.2   
N2O = 325

Radiative forcing, 2002 to 2012
CO2 = 0.28 Watts per square meter
CH4 = 0.02 Watts per square meter

CO2 to CH4 ratio: 17.39

And here is the most recent ten-year period (2007-2017):

2007 concentrations of gases
CO2 = 384.8      
CH4   = 1786.9
N2O = 321.6

2017 concentrations: see above

Radiative forcing, 2007 to 2017
CO2 = 0.27 Watts per square meter
CH4 = 0.03 Watts per square meter

CO2 to CH4 ratio: 9.71

Sources:

1750 concentrations:
http://cdiac.ess-dive.lbl.gov/pns/current_ghg.html

Recent concentrations:
https://www.esrl.noaa.gov/gmd/aggi/NOAA_MoleFractions_2018.csv

Methods:
https://agupubs.onlinelibrary.wiley.com/doi/epdf/10.1002/2016GL071930

I acknowledge that climate change is both complex and chaotic, and consequently measuring fundamental physical properties (like the ratio of GWP10 between CO2 and CH4) over short time periods can/will distort the calculated result that one finds (see Tamino's write-up on this topic).

Title: "Don’t Settle for Easy Answers about Global Warming"

https://tamino.wordpress.com/2018/08/18/dont-settle-for-easy-answers-about-global-warming/#more-10022

Extract: "You are not a dummy. But climate deniers treat you that way.

 That’s because they know that easy answers, the simpleton’s way of dealing with things, is so easy to digest and internalize that even you, and other smart people like you, are likely to digest and internalize it."

Clearly, the time period that I cited gives a distorted answer due to the chaotic gas concentrations over different periods.  If you disagree with my fundamental point then please provide a clear explanation of what AR5 Chapter 8 Figure 8.32 is intended to convey to the public regarding the ratio of GWP10 between CO2 & CH4.

But getting to the heart of Tamino's argument.  Climate change is complex, and making simplifying assumptions can/will distort the conclusions that decision makers need to draw in order to avoid severe climate consequences in the coming decades, when we exceed the GMSTA transition range of 1.5 to 2C leading to accelerating positive feedback mechanisms.

For example, in the attached image relevant to AR5 forcing agents, you made the point that the values in this graph includes all forcing agents particularly the negative forcings from land use and aerosols.  However, AR5 assumes land use forcing from the permafrost regions to be the same in the coming decades as everywhere else, which is incorrect.  Furthermore, the impact of aerosols assumed in AR5 has subsequently be demonstrated to be meaningfully different than assumed by AR5.  In other words, garbage in - garbage out.

Again, as all of the most accurate atmospheric chemistry available has been included in the ACME projections, why doesn't the DOE make recommendations to the current policymakers based on what is the most accurate information available to date to make decisions, rather than playing number games to allow continuing methane emissions from shale gas and big ag.

Title: Re: Comparison: forcings from CO2, CH4, N2O
Post by: magnamentis on August 22, 2018, 05:05:20 PM
one of the most interesting exchanges since long, keep going, a lot to learn here.
Title: Re: Comparison: forcings from CO2, CH4, N2O
Post by: AbruptSLR on August 22, 2018, 05:23:55 PM
one of the most interesting exchanges since long, keep going, a lot to learn here.

magnamentis,

After over 15,500 posts I have made these same points many times, & I have other things to do, so I will repeat myself once again only very briefly here:

1. Land use forcing from the permafrost will likely provide positive forcing by 2050 for a variety of reasons including thermokarst lake methane emissions.
2. Negative forcing from aerosols for the past have likely been underestimated in AR5 (thus masking a higher ECS value), and as society reduces anthropogenic aerosol emissions, the true ECS will both become apparent and will be accelerated by continued warming.
3. Rapidly cutting short-term radiative forcing agents (like methane) is likely a much more effective way to stay below the 1.5 to 2C range, rather than implementation of the negative emissions technology assumed by most IPCC scenarios in the next few decades.

Finally, I note that the IPCC uses TCR instead of ECS in their carbon budget calculations, which contributes to the illusion that we still have time to fool around with cutting anthropogenic WMGHG emissions.

See:
Title " TCR - Transient climate response"

https://www.ipcc.ch/ipccreports/tar/wg1/345.htm
Title: Re: Comparison: forcings from CO2, CH4, N2O
Post by: GoSouthYoungins on August 22, 2018, 06:09:06 PM
I'm talking about how much CH4 and CO2 warmed the atmosphere in 1750, and how much they each will warm the atmosphere in 2018, and then 2018 values minus 1750 values. I'm quite sure this is relevant, and I'm quite sure the value for CH4 has increased more than CO2. But nobody ever puts it in these terms. Which leads many to the idea that the methane has a tiny impact.

1750 concentrations of gases
CO2 = 280 ppm
CH4   = 722 ppb
N2O = 270 ppm

2017 concentrations
CO2 = 405
CH4   = 1849.7
N2O = 329.7

Radiative forcing, 1750 to 2017
CO2 = 1.99 Watts per square meter
CH4 = 0.63 Watts per square meter

CO2 to CH4 ratio: 3.17

Sources:

1750 concentrations:
http://cdiac.ess-dive.lbl.gov/pns/current_ghg.html

Recent concentrations:
https://www.esrl.noaa.gov/gmd/aggi/NOAA_MoleFractions_2018.csv

Methods:
https://agupubs.onlinelibrary.wiley.com/doi/epdf/10.1002/2016GL071930

Awesome, we are starting to get somewhere.

Now, a little reverse engineering of the maths...

125      CO2 ppm change for 2      watts/sm
1.125   CH4 ppm change for 0.63  watts/sm

125/1.125 = 2/0.63x          therefore x = 31.5

So from this it seems to me like the GWP100 is being used to calculate the amount of warming that would occur in one year. And that doesn't make any sense. It is by no means, only your calculations where this is the case. It is, sadly, ubiquitous.

There is no way it makes sense that CH4 GWP100 = 30, GWP20 = 90, GWP1 = 30.

This is obviously an over simplification but if CH4 is "active" for 12 years and that yields a multiplier of 90 over a 20 year period, during the first 12 years the implied multiplier is 150. The same simple math for figures cited for 100 years imply an initial multiplier of 250.

Now, I understand that isn't this simply. This is usually when I get told that I'm a simpleton and should leave the science to the scientist. And then there is a deafening silence as I wait to be told how it DOES work.

I'm pretty sure, that in a one year period, a methane molecule causes 100-300 times more warming than a CO2 molecule. (If that is not the case, please explain and/or cite something that explains why it is not.) If that is the case, then the increase in methane since 1750 will cause more warming this year than the increase in CO2 since 1750 will cause this year.
Title: Re: Comparison: forcings from CO2, CH4, N2O
Post by: AbruptSLR on August 22, 2018, 06:13:57 PM
The linked reference discusses some of consensus sciences efforts to better account for the climate impacts of short-lived climate pollutants (SLCPs) including methane, for better climate decision making.  But even these efforts do not appropriately address the risks of cascading tipping points for positive feedback mechanisms over the coming decades:

Myles R. Allen et al. (2018), "A solution to the misrepresentations of CO2-equivalent emissions of short-lived climate pollutants under ambitious mitigation", npj Climate and Atmospheric Science 1, Article No. 16; Doi: https://doi.org/10.1038/s41612-018-0026-8

https://www.nature.com/articles/s41612-018-0026-8

Extract: "While cumulative carbon dioxide (CO₂) emissions dominate anthropogenic warming over centuries, temperatures over the coming decades are also strongly affected by short-lived climate pollutants (SLCPs), complicating the estimation of cumulative emission budgets for ambitious mitigation goals.  Using conventional Global Warming Potentials (GWPs) to convert SLCPs to "CO₂-equivalent" emission misrepresents their impact on global temperature."
Title: Re: Comparison: forcings from CO2, CH4, N2O
Post by: Ned W on August 22, 2018, 06:46:32 PM
Clearly, the time period that I cited gives a distorted answer due to the chaotic gas concentrations over different periods.  If you disagree with my fundamental point then please provide a clear explanation of what AR5 Chapter 8 Figure 8.32 is intended to convey to the public regarding the ratio of GWP10 between CO2 & CH4.

I would gently suggest that you should be careful about your terminology because the concepts behind the terms are different and mean very different things.

(1) What I showed (and what this thread is about) is radiative forcing, the number of additional watts per square meter of absorbed radiation at the tropopause, based on all molecules residing in the atmosphere at a given time.  Again, units are in W/m2.

(2) GWP is a ratio of the time-integrated radiative forcing for a fixed quantity of a given gas, relative to the integrated forcing from the same quantity of CO2, over a particular time period.  As such, it's a unitless ratio.

(3) What Fig. 8.32 shows is the global mass of emissions from the year 2008, for various gases converted to CO2-equivalent mass by weighting them using GWP for selected time horizons.  Note that this is not the concentration-based CO2e quantity that we've been talking about elsewhere, it's mass-based, so the units are in Pg.

Those three things are very different, and it's hard to talk about them in a way that is sensible unless all participants in the conversation are clear on what is meant. 

I know this probably sounds obnoxiously academic and persnickety.  It's natural to say "You know what I mean, why don't you just answer the question?"  The problem is that often in this thread it's not at all clear what people are trying to ask about because subtle differences in the use of terminology can lead to very different answers.  Worse yet, some questions literally make no sense in the way they are posed (some of GSY's posts fell into that category).

So my graphs in this thread show the net change in the Earth's radiation balance caused by all the methane and all the CO2 in its atmosphere during your 10-year period (or whatever time period you want), regardless of when it was emitted or whether it was from an anthropogenic or natural source.

What the IPCC figure shows is what mass of CO2 a single year's (anthropogenic-only) emission of methane etc. would be equivalent to, when considering how much radiative forcing that 1 year's mass of emissions would produce during an ensuing 10-year, 20-year, and 100-year time period.

Those are two completely different things!  It is not that one of them is "right" and the other is "wrong".  They are answers to different questions.

Having said that, I am really at a loss as to the focus by multiple people in this thread on very short timescale values for GWP (1 or 10 years).  Nobody in the real world that I know of uses GWP at such short timescales for anything, because it gives answers that are dangerously misleading unless you really understand what is going on. 

And this thread is not even about GWP at all ... it only keeps flooding back in here because a lot of people on ASIF do not understand what radiative forcing means or what GWP is or why they are different. 

After the past few days of this, my desk has a dent in it from me pounding my forehead on it...

 :-\
Title: Re: Comparison: forcings from CO2, CH4, N2O
Post by: Ned W on August 22, 2018, 06:57:06 PM
Now, a little reverse engineering of the maths...

125      CO2 ppm change for 2      watts/sm
1.125   CH4 ppm change for 0.63  watts/sm

125/1.125 = 2/0.63x          therefore x = 31.5

So from this it seems to me like the GWP100 is being used to calculate the amount of warming that would occur in one year.

No, you said you wanted 1750 to the present (2017) so it's the amount of "warming" (or actually radiative forcing) that would occur over 267 years.  Not one year.

If CO2 were increasing by 125 ppm in one year, we would be in deep trouble indeed.
Title: Re: Comparison: forcings from CO2, CH4, N2O
Post by: AbruptSLR on August 22, 2018, 07:08:43 PM
Having said that, I am really at a loss as to the focus by multiple people in this thread on very short timescale values for GWP (1 or 10 years).  Nobody in the real world that I know of uses GWP at such short timescales for anything, because it gives answers that are dangerously misleading unless you really understand what is going on. 

And this thread is not even about GWP at all ... it only keeps flooding back in here because a lot of people on ASIF do not understand what radiative forcing means or what GWP is or why they are different. 

After the past few days of this, my desk has a dent in it from me pounding my forehead on it...

 :-\

I am sorry for the portion of the dent in your desk that I have contributed; and I appreciate your point that it is important to not to compare apples to oranges.  That said, I am concerned that overly simple calculations and even Earth System Models of intermediate complexity ignore fundamental facts that indicate the risk of abrupt climate change in the coming decades both in the paleorecord (the first image shows how rapidly Arctic Amplification can occur relative to our current state) and in more advanced computer models (that rigorously account for all of the issues of units that you raised) like the second image by Brown & Caldeira 2017 with ECS calibrated to the paleo record, and the third image that shows that the posterior ECS for the HadGEM2-ES model shows that ECS could well be in the 6C range soon without effective action.

So if the point of your comparison of the forcings for CO2 and CH4 and N2O is that no immediate action is needed to cut back on CH4 and N20 emissions, then I do not concur.
Title: Re: Comparison: forcings from CO2, CH4, N2O
Post by: GoSouthYoungins on August 22, 2018, 07:12:51 PM
No. I said I wanted the difference in warming, caused by the difference in specific GHGs this year VS 1750. So the present concentration, minus the pre industrial concentration, and how much warming would be caused by the additional gases. How much warming CH4 causes in the year 2018 minus how much warming CH4 caused in 1750. And the same for CO2. (I think I was off by 2.75, due to my failure to grasp the mass vs concentration in different metrics.)

To figure out how much warming would be caused by a gas relative to CO2, wouldn't that be GWP1, multiplied by concentration and divided by mass ratio?

Is GWP1 basically RF / mass-ratio?

Why can't GWP1 or GWP10 be easily approximately calculated?

Why is GWP given for mass, when GHGs are typically measured in molecule concentration?

Title: Re: Comparison: forcings from CO2, CH4, N2O
Post by: Ned W on August 22, 2018, 07:58:58 PM
So if the point of your comparison of the forcings for CO2 and CH4 and N2O is that no immediate action is needed to cut back on CH4 and N20 emissions, then I do not concur.

Thanks, but that is not at all my point.  I think sometimes people here are so used to arguing with deniers elsewhere that they overreact to things a bit on ASIF.

My point is that in the recent past and present, methane forcing is fairly small relative to CO2 forcing.

I don't generally post much about policy/mitigation topics.  But since you raised the question of whether we should be emphasizing immediate action to cut back on CH4 emissions, I'd point this out:

The things that most people here seem to worry about are methane feedbacks not direct anthropogenic emissions of methane.  Permafrost, clathrates, the thermokarst lakes that you mention.  But if that's what you worry about, it doesn't follow that the way to prevent those feedbacks from kicking in is by addressing anthropogenic emissions of methane.  You want to prevent warming, however that can be done most efficiently.

Maybe part of that is reducing anthropogenic emissions of methane.  But look at the forcing data -- those aren't currently what is driving the warming right now, today!  It's mostly CO2.  So without knowing much about mitigation pathways and cost/benefit policy analysis, it seems to me that reducing CO2 would be much more important for preventing the hypothetical future Methane Feedback Apocalypse.

Again, though, that is veering far off topic, and as I said I have no particular strong feelings about policy/mitigation issues.
Title: Re: Comparison: forcings from CO2, CH4, N2O
Post by: GoSouthYoungins on August 22, 2018, 08:12:00 PM

The things that most people here seem to worry about are methane feedbacks not direct anthropogenic emissions of methane.  Permafrost, clathrates, the thermokarst lakes that you mention.  But if that's what you worry about, it doesn't follow that the way to prevent those feedbacks from kicking in is by addressing anthropogenic emissions of methane.  You want to prevent warming, however that can be done most efficiently.

Maybe part of that is reducing anthropogenic emissions of methane.  But look at the forcing data -- those aren't currently what is driving the warming right now, today!  It's mostly CO2.  So without knowing much about mitigation pathways and cost/benefit policy analysis, it seems to me that reducing CO2 would be much more important for preventing the hypothetical future Methane Feedback Apocalypse.

Again, though, that is veering far off topic, and as I said I have no particular strong feelings about policy/mitigation issues.

It sounds like you believe that if CO2 stabilized this year, then temperature would stabilize. I believe there is at minimum a decade of lag, probably 3 or 4 decades. The CO2 concentration we have now corresponds to a much hotter climate than we are currently experiencing. And bringing CO2 down if a very difficult thing to do. Methane on the other hand, gets rid on itself in a decade. With methane, we simply have to stop creating so much. Natural gas and big ag are the big culprits here. Irrespective of the additional forcing of each gas during the last few decades, going forward, dealing with methane seems a much more fruitful avenue.
Title: Re: Comparison: forcings from CO2, CH4, N2O
Post by: Ned W on August 22, 2018, 09:12:50 PM
No. I said I wanted the difference in warming, caused by the difference in specific GHGs this year VS 1750. So the present concentration, minus the pre industrial concentration, and how much warming would be caused by the additional gases. How much warming CH4 causes in the year 2018 minus how much warming CH4 caused in 1750. And the same for CO2. (I think I was off by 2.75, due to my failure to grasp the mass vs concentration in different metrics.)

To figure out how much warming would be caused by a gas relative to CO2, wouldn't that be GWP1, multiplied by concentration and divided by mass ratio?

Is GWP1 basically RF / mass-ratio?

Why can't GWP1 or GWP10 be easily approximately calculated?

Why is GWP given for mass, when GHGs are typically measured in molecule concentration?

I'm sorry, but you're going to have to find someone else to badger about this.  It's a lot more complicated than you realize.  For example, GWP is based on a time-integration of radiative forcing.  But radiative forcing for both CO2 and CH4 varies with concentration, and also depends on the concentration of N2O:

Adding 100 ppm CO2 starting from 300 ppm = 1.544 W/m2 (with N2O fixed at 300 ppm)
Adding 100 ppm CO2 starting from 400 ppm = 1.198 W/m2

So calculating GWP is not trivial.  Because CH4 (and CO2) both overlap with N2O, maybe N2O concentration has to be zero when doing this calculation?  Or has to be held fixed at some value? 

You can't just make this stuff up.  You need to know what you're doing in order to do it right.  I never use GWP in my own work and don't really want to dive down into that.  That's why I started a thread called  Comparison: forcings from CO2, CH4, N2O rather than GWP.

But given your Dunning-Krugerish contempt for the expertise of actual scientists (https://forum.arctic-sea-ice.net/index.php/topic,2383.msg168889.html#msg168889), I'm not optimistic that you'll stop mangling this stuff like a bull in a mathematical china shop.

(https://i2.wp.com/freethoughtblogs.com/pharyngula/files/2016/01/scienceveverythingelse.gif)
Title: Re: Comparison: forcings from CO2, CH4, N2O
Post by: AbruptSLR on August 22, 2018, 09:48:23 PM
You want to prevent warming, however that can be done most efficiently.

Maybe part of that is reducing anthropogenic emissions of methane.  But look at the forcing data -- those aren't currently what is driving the warming right now, today!  It's mostly CO2.  So without knowing much about mitigation pathways and cost/benefit policy analysis, it seems to me that reducing CO2 would be much more important for preventing the hypothetical future Methane Feedback Apocalypse.

Again, though, that is veering far off topic, and as I said I have no particular strong feelings about policy/mitigation issues.

For the sake of clarity, I note that, the EPA uses a GWP100 value of 25 for methane for their GHG emissions account because they made a policy decision to stay with the AR4 values:

https://www.ipcc.ch/publications_and_data/ar4/wg1/en/ch2s2-10-2.html

Nevertheless, the EPA acknowledges that the GWP100 value for methane may be as high as 36 (when account for climate-carbon feedback and aerosol interaction).  As 36/25 = 1.44 this policy decision represents a significant under accounting for the significance of methane for global warming. This is almost certainly resulting in reduced efforts to reduce methane emissions as to what would be optimal policy.

Title: "Understanding Global Warming Potentials"

https://www.epa.gov/ghgemissions/understanding-global-warming-potentials

Extract: "Methane (CH4) is estimated to have a GWP of 28–36 over 100 years"

What GWP estimates does EPA use for GHG emissions accounting, such as the Inventory of U.S. Greenhouse Gas Emissions and Sinks (Inventory) and the Greenhouse Gas Reporting Program?

The EPA considers the GWP estimates presented in the most recent IPCC scientific assessment to reflect the state of the science. In science communications, the EPA will refer to the most recent GWPs. The GWPs listed above are from the IPCC's Fifth Assessment Report, published in 2014.

The EPA's Inventory of U.S. Greenhouse Gas Emissions and Sinks (Inventory) complies with international GHG reporting standards under the United Nations Framework Convention on Climate Change (UNFCCC). UNFCCC guidelines now require the use of the GWP values for the IPCC's Fourth Assessment Report (AR4), published in 2007. The Inventory also presents emissions by mass, so that CO2 equivalents can be calculated using any GWPs, and emission totals using more recent IPCC values are presented in the annexes of the Inventory report for informational purposes.

Data collected by EPA's Greenhouse Gas Reporting Program is used in the Inventory, so the Reporting Program generally uses GWP values from the AR4. The Reporting Program collects data about some industrial gases that do not have GWPs listed in the AR4; for these gases, the Reporting Program uses GWP values from other sources, such as the Fifth Assessment Report.
EPA's CH4 reduction voluntary programs also use CH4 GWPs from the AR4 report for calculating CH4 emissions reductions through energy recovery projects, for consistency with the national emissions presented in the Inventory."
Title: Re: Comparison: forcings from CO2, CH4, N2O
Post by: GoSouthYoungins on August 22, 2018, 09:58:09 PM
(1850 ppb CH4 instantaneous forcing) minus (720 ppb CH4 instantaneous forcing) = ?????
(410 ppm CO2 instantaneous forcing) minus (290 ppm CO2 instantaneous forcing) = ?????

Why is those hard to answer? Pick some average constant concentrations for the other gases, and we should get a decent estimate.

I don't have contempt for the complexity of science. The idea that I'm just too stupid to understand that I'm stupid doesn't fly with me for a second. I always tested in the top 1% on standardized tests. I'm happy to admit that I don't have an expertise in this stuff, but that doesn't mean I'm conformable chilling with statements that fly in the face of my understanding. That's why I asked the questions that I did. And I don't respect the idea that GWP100 is a thing and GWP20 is a thing, but GWP10 or GWP1 is not.

I have contempt for a thread and graphs that show methane as having little effect on global warming. The reality is that addressing methane could have more impact in the short term than addressing any other GHG. Maybe I'm a bull in the shop of misleading and fragile ideas.
Title: Re: Comparison: forcings from CO2, CH4, N2O
Post by: TeaPotty on August 23, 2018, 04:25:43 AM
Yeah, I dont think its by accident that CH4 is downplayed. Every time CH4 research comes out that all these 1%-friendly scientists come out barking like dogs, and always argue that "all focus must remain on CO2" like a mantra.

To me, the Paris Climate Agreement was a death sentence signed by the 1%. The whole point was not just to continue with dirty fuel, but to continue the methane-natural-gas money-train, specifically the Fracking boom. The 1% dont want to cut any methane, period.
Title: Re: Comparison: forcings from CO2, CH4, N2O
Post by: Pmt111500 on August 23, 2018, 06:47:29 AM
Methane, in general, gets converted to CO2 and 2 H2O, so the airborne fraction isn't the only result of leakage of methane. I think there's no way to separate afterwards the CO2 from methane and other fossil fuels (like it is of burning wood vs. fossil fuels for instance), so the total climate impact of methane (and other natgas) can only be calculated from production numbers. This is not too important to the climate simulations.
Well, maybe you could see a slight change in methane isotopic ratios according to the change in methane source, I guess most deposits humanity uses as fuel (increasing CO2) are a bit older in average than the surface melt/rice field methane from permafrost/agriculture. But I guess the variance is so large locally it's not possible to do this routinely. And anyway, swamps outgassing this stuff can readily overwhelm (at least locally) sources of human origin. Natgas should as well be treated like any fossil fuel wrt climate change.


Title: Re: Comparison: forcings from CO2, CH4, N2O
Post by: Sleepy on August 23, 2018, 07:47:46 AM
Pmt, maybe you should change could to should? It should be treated like any other fossil fuel.

To me, the Paris Climate Agreement was a death sentence signed by the 1%. The whole point was not just to continue with dirty fuel, but to continue the methane-natural-gas money-train, specifically the Fracking boom. The 1% dont want to cut any methane, period.
Russia, France and China are also happy as pigs in shit. Six months ahead of schedule:
https://news.cgtn.com/news/3d3d774e3245444e79457a6333566d54/share_p.html (https://news.cgtn.com/news/3d3d774e3245444e79457a6333566d54/share_p.html)
Quote
According to an industry report, China is likely to become the world's largest natural gas importer by 2019 in terms of domestic short supply, with imports expected to reach 171 billion cubic meters by 2023. The majority of those imports will consist of LNG.

16 days to go before we cross the medium (and possibly overly positive) estimate for 1.5°C according to MCC.
https://www.mcc-berlin.net/fileadmin/data/clock/carbon_clock.htm (https://www.mcc-berlin.net/fileadmin/data/clock/carbon_clock.htm)

How much does it matter if we get the final blow by the CO2T-Rex or the CH4Raptor? Or the one we never saw ...
Title: Re: Comparison: forcings from CO2, CH4, N2O
Post by: Pmt111500 on August 23, 2018, 08:42:32 AM
Yes, Sleepy, correct. Still, frequently i have to check some words from dictionary, some grammar errors are also visible in my writing, still trying to lose those finnishisms and other englishwisely-odd associations used in finnish.
Title: Re: Comparison: forcings from CO2, CH4, N2O
Post by: oren on August 23, 2018, 12:36:22 PM
Posting in this very interesting thread is a major challenge due to the high scientific level of discussion. First of all, thank you Ned W for taking the time and the head-banging to clearly explain the concept of radiative forcing and its calculations, as opposed to the GWP concept.
I find myself thinking that, based on your numbers:
A. Current methane contribution to RF relative to 1750 is NOT insignificant, compared to CO2. Had there been no change in CH4 concentration at all since 1750, current RF would be much lower. You provided the numbers for this.
B. Current annual change of CH4 concentration is such that its RF annual change is small, while CO2 RF annual change is much larger. You provided the numbers for this.
C. This does NOT mean however that current annual anthropogenic emissions of CH4 are not important. Due to the short residence time of CH4 in the atmosphere, new emissions replace the old emissions and give the feeling that there is little annual change. But if we were to stop all anthropogenic emissions of CH4, its concentration would go down relatively quickly. So the RF delta value of such a policy would be significant. (Of course we do not know the amount of natural CH4 emissions, so this RF value would is not easily calculable.) OTOH, if we were to stop all CO2 emissions, we would save the annual delta of RF that is due to increasing concentration, but only a very small RF delta value thanks to naturally dropping concentration. (Of course we should stop both CH4 and CO2 but I am trying to understand the relative policy value).

As A and B are points you made yourself (hope I understood them correctly), I would like to get your opinion of C.
Title: Re: Comparison: forcings from CO2, CH4, N2O
Post by: AbruptSLR on August 23, 2018, 03:41:00 PM
C. This does NOT mean however that current annual anthropogenic emissions of CH4 are not important. Due to the short residence time of CH4 in the atmosphere, new emissions replace the old emissions and give the feeling that there is little annual change. But if we were to stop all anthropogenic emissions of CH4, its concentration would go down relatively quickly. So the RF delta value of such a policy would be significant. (Of course we do not know the amount of natural CH4 emissions, so this RF value would is not easily calculable.) OTOH, if we were to stop all CO2 emissions, we would save the annual delta of RF that is due to increasing concentration, but only a very small RF delta value thanks to naturally dropping concentration. (Of course we should stop both CH4 and CO2 but I am trying to understand the relative policy value).

I believe that at this point time it is valuable to focus on the radiative forcing contribution from anthropogenic methane emissions (as addressed in AR5 Ch 8, Figure 8.32), as cannot stop current natural methane emissions; and quickly restricting anthropogenic methane emissions is likely one of the best ways to reduce the acceleration of future natural methane emissions.
Title: Re: Comparison: forcings from CO2, CH4, N2O
Post by: Ned W on August 23, 2018, 06:03:09 PM
Posting in this very interesting thread is a major challenge due to the high scientific level of discussion. First of all, thank you Ned W for taking the time and the head-banging to clearly explain the concept of radiative forcing and its calculations, as opposed to the GWP concept.
I find myself thinking that, based on your numbers:
A. Current methane contribution to RF relative to 1750 is NOT insignificant, compared to CO2. Had there been no change in CH4 concentration at all since 1750, current RF would be much lower. You provided the numbers for this.
B. Current annual change of CH4 concentration is such that its RF annual change is small, while CO2 RF annual change is much larger. You provided the numbers for this.

Those are both correct, and very nicely and clearly stated. 

One minor wrinkle is that as the methane concentration increases, an additional increment of the same size has less warming effect.  For example:

Adding 100 ppb from 800-900 ppb warms the Earth by 0.067 W/m2 (for a given value of N2O)
But adding 100 ppb from 1800-1900 warms the Earth by only 0.044 W/m2, one-third less than before.

CO2 has a similar pattern, but methane has already increased much more (it's nearly tripled while CO2 has not even doubled yet). 

This is part of the reason why the forcing from methane emissions today is relatively small -- it takes a larger amount of emissions to produce the same degree of warming. 

Of course if it turns out that future methane feedbacks are very large, that effect will be swamped.

Quote
C. This does NOT mean however that current annual anthropogenic emissions of CH4 are not important. Due to the short residence time of CH4 in the atmosphere, new emissions replace the old emissions and give the feeling that there is little annual change. But if we were to stop all anthropogenic emissions of CH4, its concentration would go down relatively quickly. So the RF delta value of such a policy would be significant. (Of course we do not know the amount of natural CH4 emissions, so this RF value would is not easily calculable.) OTOH, if we were to stop all CO2 emissions, we would save the annual delta of RF that is due to increasing concentration, but only a very small RF delta value thanks to naturally dropping concentration. (Of course we should stop both CH4 and CO2 but I am trying to understand the relative policy value).

As A and B are points you made yourself (hope I understood them correctly), I would like to get your opinion of C.

Well. What you say makes sense intuitively, but I generally distrust my intuition on topics like that where I don't have much expertise.  All else being equal you're probably right, it's just not clear to me whether all else is in fact equal.

If our goal is to prevent future hypothetical methane feedbacks from kicking in, then we want to quickly stop warming, regardless of the source of that warming.  What you've expressed is a good argument for why reducing methane emissions might be expected to be a particularly effective way of doing that.  But all that really matters is how much "bang you can get for your buck" -- i.e., how best to spend X dollars (or, more realistically, euros) to maximize the reduction in total forcing (without causing further harm to the environment, obviously).

If reducing direct anthropogenic CH4 emissions (from fossil fuel production or whatever) is the most cost-effective way to reduce total radiative forcing, I'm in favor of that.  If something else is, I'd be in favor of that instead.   

As I keep telling people, I have no particular background in this (economics/policy/mitigation issues).  Not that I think it's unimportant, I just don't want to speculate about something outside my area of comfort.

All that said ... I will reiterate that I believe the following two things are true:
* Continued warming will cause an increased release of methane from natural sources (feedback)
* But CO2 remains the biggest problem and a certain fraction of the ASIF populace has unrealistically apocalyptic ideas about the likelihood of extremely large and sudden methane fluxes.  In a nutshell, I generally follow Gavin Schmidt's line on this.

People can feel free to yell and fling things at me now for the second point there; I'm very busy for the next few days and probably won't do much to defend myself.   :)

Maybe before the yelling starts, though, people can pause and re-read what I said 4 paragraphs up (starting with "If reducing...").  We're all on the same side here, folks, even if some of you think I'm secretly a denier.
Title: Re: Comparison: forcings from CO2, CH4, N2O
Post by: magnamentis on August 23, 2018, 07:53:54 PM
one of the most interesting exchanges since long, keep going, a lot to learn here.

magnamentis,

After over 15,500 posts I have made these same points many times, & I have other things to do, so I will repeat myself once again only very briefly here:

1. Land use forcing from the permafrost will likely provide positive forcing by 2050 for a variety of reasons including thermokarst lake methane emissions.
2. Negative forcing from aerosols for the past have likely been underestimated in AR5 (thus masking a higher ECS value), and as society reduces anthropogenic aerosol emissions, the true ECS will both become apparent and will be accelerated by continued warming.
3. Rapidly cutting short-term radiative forcing agents (like methane) is likely a much more effective way to stay below the 1.5 to 2C range, rather than implementation of the negative emissions technology assumed by most IPCC scenarios in the next few decades.

Finally, I note that the IPCC uses TCR instead of ECS in their carbon budget calculations, which contributes to the illusion that we still have time to fool around with cutting anthropogenic WMGHG emissions.

See:
Title " TCR - Transient climate response"

https://www.ipcc.ch/ipccreports/tar/wg1/345.htm

a) thanks for the info  but:

b) i don't see the relation between my post that you quoted and your reply like if i had said anything that would oppose or favour anything posted here. i simply stated that this thread is very interesting for me who knows little of all this and that as a result there is a lot to learn from my side and that means appreciation for the contributors.

perhaps you can elaborate which part of my short sentence triggered that " i say it once and for all "  expression which is one i'd use once i'm annoyed about someones ignorance ;)
Title: Re: Comparison: forcings from CO2, CH4, N2O
Post by: oren on August 23, 2018, 10:49:45 PM
Thanks Ned for your detailed response.
Title: Re: Comparison: forcings from CO2, CH4, N2O
Post by: AbruptSLR on August 23, 2018, 11:04:25 PM
b) i don't see the relation between my post that you quoted and your reply like if i had said anything that would oppose or favour anything posted here. i simply stated that this thread is very interesting for me who knows little of all this and that as a result there is a lot to learn from my side and that means appreciation for the contributors.

perhaps you can elaborate which part of my short sentence triggered that " i say it once and for all "  expression which is one i'd use once i'm annoyed about someones ignorance ;)

I believe that I was tired when I made my reply; which explains why I sounded annoyed.  Only that and nothing more. ;)
Title: Re: Comparison: forcings from CO2, CH4, N2O
Post by: Rod on August 24, 2018, 04:53:18 AM
Thank you Ned W for your great analysis on this issue.   I am one of the ASIF members who is very concerned about potential future feedbacks from natural methane emissions. 

However, I think this conversation has gone a little bit sideways because people have unrealistic ideas about what the "numbers" can tell us.   We all can agree that methane has a larger warming potential than CO2 molecule per molecule.   But it is impossible to accurately measure that number on any time scale because they both behave differently in the atmosphere. 

C02 is relatively stable in the atmosphere, while CH4 is rapidly broken down by hydroxyl radicals. The amount of hydroxyl radicals in the atmosphere at any given time is almost impossible to predict.  Therefore, CH4 is assigned numbers for warming potential relative to CO2 at given periods of time based on our best guess of how fast the CH4 will be broken down. 

It does not matter if you use the warming potential for 10 years or 20 years or 50 years.  They are all just estimates.  But again, we know CH4 is more powerful than CO2 when it is there. 

The main point that seems to be getting lost in this discussion is that CO2 is currently present in the atmosphere in parts per million volume, while CH4 is currently present in the atmosphere in parts per billion volume.  That is a 1000 fold difference. 

So even if a molecule of CH4 has 100 times more warming potential than CO2 (calculated on a short term time scale) it is still present at a concentration 1000 times less than CO2 (currently).

I personally am concerned that future CH4 emissions from natural sources are going to be a big problem.  But right now, I agree the big player is still CO2.  The current levels of CH4 caused by anthropogenic releases are not insignificant.  However, their overall warming effects remain small compared to the anthropogenic releases of CO2.

If we can only pick one problem to battle, then CO2 is where the most "bang for our buck" can be achieved.  Unfortunately, we need to do something pretty quick or I believe natural releases of CH4 will start to overload the system and we might be screwed. 

I certainly could be wrong, but it seems most prudent to address all uses of fossil fuels at the same time rather than parse them out based upon their current warming potential. 
Title: Re: Comparison: forcings from CO2, CH4, N2O
Post by: AbruptSLR on August 24, 2018, 06:15:26 PM
As I have previously noted most people really care about effective radiative forcing and that current (AR5) energy balance methodologies for determining radiative feedback are inaccurate and biased.  The linked reference provide a new framework for improved estimates of radiative feedback.

Cristian Proistosescu et al. (14 May 2018), "Radiative Feedbacks From Stochastic Variability in Surface Temperature and Radiative Imbalance", Geophysical Research Letters, https://doi.org/10.1029/2018GL077678

https://agupubs.onlinelibrary.wiley.com/doi/abs/10.1029/2018GL077678

Abstract
Estimates of radiative feedbacks obtained by regressing fluctuations in top‐of‐atmosphere (TOA) energy imbalance and surface temperature depend critically on the sampling interval and on assumptions about the nature of the stochastic forcing driving internal variability. Here we develop an energy balance framework that allows us to model the different impacts of stochastic atmospheric and oceanic forcing on feedback estimates. The contribution of different forcing components is parsed based on their impacts on the covariance structure of near‐surface air temperature and TOA energy fluxes, and the framework is validated in a hierarchy of climate model simulations that span a range of oceanic configurations and reproduce the key features seen in observations. We find that at least three distinct forcing sources, feedbacks, and time scales are needed to explain the full covariance structure. Atmospheric and oceanic forcings drive modes of variability with distinct relationships between temperature and TOA radiation, leading to an effect akin to regression dilution. The net regression‐based feedback estimate is found to be a weighted average of the distinct feedbacks associated with each mode. Moreover, the estimated feedback depends on whether surface temperature and TOA energy fluxes are sampled at monthly or annual time scales. The results suggest that regression‐based feedback estimates reflect contributions from a combination of stochastic forcings and should not be interpreted as providing an estimate of the radiative feedback governing the climate response to greenhouse gas forcing.
Plain Language Summary
Climate sensitivity quantifies the long‐term warming the Earth will experience in response to the additional energy trapped in the system due to greenhouse gases. The physical processes that ultimately determine climate sensitivity—termed climate feedbacks—have been extensively investigated using information from natural variability in Earth's temperature and net energy imbalance. However, a complete physical model for what controls this natural variability has been lacking. We derive such a physical model and calibrate it to a hierarchy of numerical climate simulations of increasing complexity. We are able to answer several outstanding questions about previous estimates of climate feedbacks and sensitivity drawn from natural variability, such as what is the source of this variability, and how the estimates depend on the how the data is analyzed. We find that at least three different mechanisms for natural variability are needed to explain the relationship between temperature and energy imbalance and that none provide direct estimates of climate sensitivity.

See also:

Title: "New Modeling Framework Improves Radiative Feedback Estimates"

https://eos.org/research-spotlights/new-modeling-framework-improves-radiative-feedback-estimates?utm_source=eos&utm_medium=email&utm_campaign=EosBuzz082418

Extract: "A new approach offers insights into the relationship between surface temperature and top-of-atmosphere energy imbalances and improves the understanding of important climate feedbacks.

The novel application of the Hasselmann model provides researchers with a new approach to explain the relationship between top-of-atmosphere fluxes and surface temperatures and offers useful insight into the natural variability of radiative feedbacks. The framework also improves estimates of radiative feedback that may currently be inaccurate and biased."
Title: Re: Comparison: forcings from CO2, CH4, N2O
Post by: Ned W on August 24, 2018, 09:35:54 PM
As I have previously noted most people really care about effective radiative forcing and that current (AR5) energy balance methodologies for determining radiative feedback are inaccurate and biased.  The linked reference provide a new framework for improved estimates of radiative feedback.

And as I have previously noted after you previously noted that (https://forum.arctic-sea-ice.net/index.php/topic,2383.msg168794.html#msg168794), for the greenhouse gases discussed in this thread, ERF is almost identical to the (much simpler) stratospherically-adjusted RF.  For example, the ERF for CO2 is something like 2% lower than regular old RF.

See page 667 of AR5, starting with "In many cases, however, ERF and RF are nearly equal...."

So for our purposes here, the distinction between ERF and RF is irrelevant. 

 :)

But also ... from a quick glance, that paper doesn't have anything to do with ERF.  I'm rather at a loss for what you were thinking there.  The paper really has nothing to do with your introduction of it ("As I have previously noted most people really care about effective radiative forcing ....")

Radiative forcing is not the same as radiative feedback.
Title: Re: Comparison: forcings from CO2, CH4, N2O
Post by: Ned W on August 24, 2018, 09:49:23 PM
On further perusal of that paper, my only reaction is "WTF?" 

It doesn't really have anything to do with the thread topic.  At all.

It doesn't really follow up on anyone else's post in this thread.

It doesn't have anything to do with the two things you mentioned in your introduction to it (ERF vs RF, and gratuitous bashing of AR5). 

So maybe you could elaborate on what specifically in that paper caused you to post it here.
Title: Re: Comparison: forcings from CO2, CH4, N2O
Post by: AbruptSLR on August 24, 2018, 11:01:49 PM
Radiative forcing is not the same as radiative feedback.

Radiative feedback is more relevant to effective radiative forcing, ERF.  The value of talking about ERF in stead of RF is discussed in the linked reference:

Forster, P. M., T. Richardson, A. C., Maycock, C. J. Smith, B. H. Samset, G. Myhre, T. Andrews, R. Pincus, and M. Schulz (2016), "Recommendations for diagnosing effective radiative forcing from climate models for CMIP6", J. Geophys. Res. Atmos., 121, 12,460–12,475, doi:10.1002/2016JD025320.

https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1002/2016JD025320

Abstract: "The usefulness of previous Coupled Model Intercomparison Project (CMIP) exercises has been hampered by a lack of radiative forcing information. This has made it difficult to understand reasons for differences between model responses. Effective radiative forcing (ERF) is easier to diagnose than traditional radiative forcing in global climate models (GCMs) and is more representative of the eventual temperature response. Here we examine the different methods of computing ERF in two GCMs. We find that ERF computed from a fixed sea surface temperature (SST) method (ERF_fSST) has much more certainty than regression based methods. Thirty year integrations are sufficient to reduce the 5–95% confidence interval in global ERF_fSST to 0.1Wm2. For 2xCO2 ERF, 30 year integrations are needed to ensure that the signal is larger than the local confidence interval over more than 90% of the globe. Within the ERF_fSST method there
are various options for prescribing SSTs and sea ice. We explore these and find that ERF is only weakly dependent on the methodological choices. Prescribing the monthly averaged seasonally varying model’s preindustrial climatology is recommended for its smaller random error and easier implementation. As part of CMIP6, the Radiative Forcing Model Intercomparison Project (RFMIP) asks models to conduct 30 year ERF_fSST experiments using the model’s own preindustrial climatology of SST and sea ice. The Aerosol and Chemistry Model Intercomparison Project (AerChemMIP) will also mainly use this approach. We propose this as a standard method for diagnosing ERF and recommend that it be used across the climate modeling community to aid future comparisons."
Title: Re: Comparison: forcings from CO2, CH4, N2O
Post by: Ned W on August 24, 2018, 11:30:42 PM
Earlier I'd pointed out that the way you were comparing the RCP 8.5 CO2eq to actual measurements was inappropriate ("apples-to-oranges"). 

But rather than just criticizing someone else for doing something wrong, it's better to actually do it right.  So here's the proper comparison.  I recalculated CO2eq for RCP 8.5 (and the other pathways) using the same definition that NOAA AGGI uses (basically, all well-mixed greenhouse gases):

(https://i.imgur.com/vwqW0tX.png)

So RCP 8.5 is overestimating CO2eq by about 5 ppm, instead of underestimating it by 100 ppm.  That's a bit more reassuring. 

The other pathways are slightly underestimating CO2eq, by 1 to 3 ppm.

Since I'm interested in comparisons of forcing among different greenhouse gases, and particularly interested in the post-2012 period (i.e., after the CMIP5 models were published), here are the recent (2012-2017) forcings, broken down by greenhouse gas:

(https://i.imgur.com/GzUXHSZ.png)

So far, RCP 8.5 is overestimating the recent forcings from methane (significantly) and CO2 (slightly).  It's slightly underestimating the forcings from N2O, CFC-11, and CFC-12.

The one caveat is that I used the forcing values directly from NOAA AGGI and CMIP5, rather than recalculating them from raw concentrations using the Etminan et al. formulas.  That would have basically raised everything across the board by about 10 ppmv.  It shouldn't have had much effect on how the different RCPs did, or on what's being under vs over-estimated.

Since you are so enthusiastic about ERFs, I'd love to see these calculations redone using ERFs, and then converted to CO2eqs.  Feel free to do that, if you think it would make any non-trivial difference in the results.  NOAA AGGI are here (https://www.esrl.noaa.gov/gmd/aggi/aggi.html).  CMIP5 RCPs are here (http://www.pik-potsdam.de/~mmalte/rcps/).

Title: Re: Comparison: forcings from CO2, CH4, N2O
Post by: sidd on August 24, 2018, 11:50:01 PM
Thanks Mr. Ned W. Very clear.

sidd
Title: Re: Comparison: forcings from CO2, CH4, N2O
Post by: AbruptSLR on August 25, 2018, 12:34:03 AM
I recalculated CO2eq for RCP 8.5 (and the other pathways) using the same definition that NOAA AGGI uses (basically, all well-mixed greenhouse gases):

I previously pointed out in Reply #86 that the EPA uses (and here I provide a link below that NOAA also uses) a GWP100 for methane of 25 (based on Ramaswamy et al., 2001, and used in TAR and AR4) instead of 36 as cited in AR5 and by Shindell et at (2009) as linked in Reply #57.  This means that your calculations use GWP values for methane that are much lower than accepted by current consensus science (but I suspect that you already know all of this; which is likely why you used NOAA's out of date methodology to support your out of date point):

See: Title: "THE NOAA ANNUAL GREENHOUSE GAS INDEX (AGGI)"

https://www.esrl.noaa.gov/gmd/aggi/aggi.html

Extract: "Table 1. Expressions for Calculating Radiative Forcing*

*IPCC (2001)"

And see:

Title: "2.10.2 Direct Global Warming Potentials"

https://www.ipcc.ch/publications_and_data/ar4/wg1/en/ch2s2-10-2.html

Also see:

Drew T. Shindell et al. (18 February 2005), "An emissions‐based view of climate forcing by methane and tropospheric ozone", Geophysical Research Letters, https://doi.org/10.1029/2004GL021900

https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2004GL021900

Extract: "We have calculated the instantaneous tropopause radiative forcing due to emissions‐induced changes in methane and ozone (Figure 1). The standard abundance‐based view [Ramaswamy et al., 2001] is shown for comparison."

Caption for Figure 1: "Radiative forcing from the preindustrial (1750) to the present‐day (1998). Values above or below the bars give the total forcing, while values in parentheses give the forcing due to methane emissions alone. The abundance‐based ozone value is from the sum of simulations with individual emission reductions for consistency with the emissions‐based values. Forcing of ∼0.1 W m−2 from stratospheric H2O generated by methane is not included. For comparison, the abundance‐based forcing from CO2 is 1.46 W m−2. Uncertainties in the abundance‐based values are 0.13 for methane, based on the ∼40% spread in forcing per unit methane estimates [Hansen et al., 1997; Ramaswamy et al., 2001], and 0.09 for ozone, based on the spread in model results [Ramaswamy et al., 2001]. For emissions‐based values, we estimate uncertainties by adding the direct methane forcing uncertainty given above in quadrature with the standard deviations in models' responses of ozone to individual emissions from Prather et al. [2001]. This yields 0.17 for methane, 0.10 for CO + VOCs (using the VOC value for CO), and 0.06 for NOx. Uncertainty in the net forcing from non‐methane ozone precursors is 0.11. Note that the emissions‐based values are approximate, as the models of Prather et al. [2001] used substantially different perturbations than those used here, and the VOC perturbation was done simultaneously with CH4 (we assume the uncertainty is dominated by VOCs)."

Title: Re: Comparison: forcings from CO2, CH4, N2O
Post by: AbruptSLR on August 25, 2018, 12:35:37 AM
Thanks Mr. Ned W. Very clear.

sidd

It appears to me that you are encouraging Ned W to use out of date methodology/values for calculating radiative forcing. :o
Title: Re: Comparison: forcings from CO2, CH4, N2O
Post by: Ned W on August 25, 2018, 02:46:51 AM
I previously pointed out in Reply #86 that the EPA uses (and here I provide a link below that NOAA also uses) a GWP100 for methane of 25 (based on Ramaswamy et al., 2001, and used in TAR and AR4) instead of 36 as cited in AR5 and by Shindell et at (2009) as linked in Reply #57.  This means that your calculations use GWP values for methane that are much lower than accepted by current consensus science (but I suspect that you already know all of this; which is likely why you used NOAA's out of date methodology to support your out of date point):

Nope.  You're confused again.

There is a minor improvement that could be made to the forcing calculations used above (updating them per Etminan et al. 2016) but doing so would have little impact on the results because it would affect both the observations (NOAA AGGI) and scenario data (RCPs) similarly.

And back on page 1 of this thread you actually endorsed the same forcing values you're now attacking...
Title: Re: Comparison: forcings from CO2, CH4, N2O
Post by: Ned W on August 25, 2018, 04:00:54 AM
Since sidd kindly complimented my efforts at clarity, I should try to be more clear here as well.  ASLR is once again comparing apples to oranges, and blaming oranges for not being apples.

Emissions-based and abundance-based forcing metrics are two different ways of quantifying the effect of GHGs on the Earth's radiation balance.  They are different things, each have their own virtues and problems, and are intended to answer different questions.  One is not objectively "right" and the other "wrong". 

To make matters worse, ASLR conflates this distinction (abundance-based vs emissions-based forcings) with conceptually unrelated issues about how to calculate GWP. 

The methods used to calculate radiative forcing in NOAA's AGGI are also used in IPCC AR5 (contrary to what ASLR claims) and almost everywhere else as well, including the ORNL web page that ASLR himself approvingly linked to back on the first page of this thread:

The total radiative forcings, RFs, from the linked ORNL website article by Blasing, T.J. (that updates such RF values reported in April 2016) are used in the linked Wikipedia article to calculate a CO2e value of 526.6ppm:

https://en.wikipedia.org/wiki/Carbon_dioxide_equivalent

Extract: "To calculate the CO2e of the additional radiative forcing calculated from April 2016's updated data: ∑ RF(GHGs) = 3.3793, thus CO2e = 280 e3.3793/5.35 ppmv = 526.6 ppmv."

http://cdiac.ornl.gov/pns/current_ghg.html

Forcings from ORNL (ASLR likes these):
CO2 = 1.94
CH4 = 0.50
N2O = 0.20

Forcings from AGGI (ASLR doesn't like these):
CO2 = 1.94
CH4 = 0.50
N2O = 0.19

Well, the N2O one isn't quite identical, I guess (joke -- it's a rounding issue.)
Title: Re: Comparison: forcings from CO2, CH4, N2O
Post by: sidd on August 25, 2018, 05:44:53 AM
"It appears to me that you are encouraging Ned W to use out of date methodology/values for calculating radiative forcing."

And it appears to me that Mr. Ned W. has the better arguments, and the better math.

sidd
Title: Re: Comparison: forcings from CO2, CH4, N2O
Post by: AbruptSLR on August 25, 2018, 05:37:00 PM
"It appears to me that you are encouraging Ned W to use out of date methodology/values for calculating radiative forcing."

And it appears to me that Mr. Ned W. has the better arguments, and the better math.

sidd

sidd,

When you are wrong you like to double down.

Title: Re: Comparison: forcings from CO2, CH4, N2O
Post by: AbruptSLR on August 25, 2018, 05:42:27 PM

Forcings from ORNL (ASLR likes these):
CO2 = 1.94
CH4 = 0.50
N2O = 0.20


Just because I do not challenge every line of your incorrect values does not mean that I like your values, it means that I do not think that correct every line of your values are not worth my effort.

From my Reply #24, I like the following values:

The total radiative forcings, RFs, from the linked ORNL website article by Blasing, T.J. (that updates such RF values reported in April 2016) are used in the linked Wikipedia article to calculate a CO2e value of 526.6ppm:

https://en.wikipedia.org/wiki/Carbon_dioxide_equivalent


Extract: "To calculate the CO2e of the additional radiative forcing calculated from April 2016's updated data: ∑ RF(GHGs) = 3.3793, thus CO2e = 280 e3.3793/5.35 ppmv = 526.6 ppmv."

http://cdiac.ornl.gov/pns/current_ghg.html

Per the following linked NOAA website the change in CO2e in 2017 was 4 ppm, which would give a total CO2e at the end of 2017 of about 530.6 ppm

https://www.esrl.noaa.gov/gmd/aggi/aggi.html
Title: Re: Comparison: forcings from CO2, CH4, N2O
Post by: Ned W on August 25, 2018, 06:36:50 PM

Forcings from ORNL (ASLR likes these):
CO2 = 1.94
CH4 = 0.50
N2O = 0.20


Just because I do not challenge every line of your incorrect values does not mean that I like your values, it means that I do not think that correct every line of your values are not worth my effort.

From my Reply #24, I like the following values:

The total radiative forcings, RFs, from the linked ORNL website article by Blasing, T.J. (that updates such RF values reported in April 2016) are used in the linked Wikipedia article to calculate a CO2e value of 526.6ppm:

https://en.wikipedia.org/wiki/Carbon_dioxide_equivalent


Extract: "To calculate the CO2e of the additional radiative forcing calculated from April 2016's updated data: ∑ RF(GHGs) = 3.3793, thus CO2e = 280 e3.3793/5.35 ppmv = 526.6 ppmv."

http://cdiac.ornl.gov/pns/current_ghg.html

Click on your own link to the Blasing T.J. page at ORNL/CDIAC. 

Scroll down to the table.

Look at the right-most column ("Increased radiative forcing 6 (W/m2)").

Look at the first three rows of this column, for CO2, CH4, and N2O.

Now compare them to what I posted above.

....

This is, literally, the third time you have specifically endorsed and promoted a set of values for radiative forcing of CO2, CH4, and N2O that you claim are obsolete and wrong when I use them. 

Title: Re: Comparison: forcings from CO2, CH4, N2O
Post by: AbruptSLR on August 25, 2018, 06:52:44 PM

This is, literally, the third time you have specifically endorsed and promoted a set of values for radiative forcing of CO2, CH4, and N2O that you claim are obsolete and wrong when I use them.

All of your arguments ignore the aerosol interaction contribution (as cited in Shindell's research) to methane's radiative forcing which is required to get up to a GWP100 of 36 for methane.  I see no point in continuing this dialog when you seem to think that you are entitled to use a GWP100 of 25 (or so) for methane.

Edit, see & the associated image:

Shindell, D.T., Faluvegi, G., Koch, D.M., Schmidt, G.A., Unger, N., and Bauer S.E. (2009), "Improved Attribution of Climate Forcing to Emissions" Science, Vol. 326 no. 5953 pp. 716-718, DOI: 10.1126/science.1174760.

http://saive.com/911/DOCS/AAAS-Aerosols-not-CO2-Cause-Global-Warming.pdf

Note also that when methane is chemically converted to carbon dioxide in the atmosphere I count the radiative forcing from that carbon dioxide molecule to the original methane molecule, which adds another 1 to the effective GWP100 for methane.

Edit 2: When considering ERF the direct and indirect aerosol contributions can clearly be attributed to the methane emission, as without the methane emission those contributions would not occur.
Title: Re: Comparison: forcings from CO2, CH4, N2O
Post by: Ned W on August 25, 2018, 08:55:43 PM
Where did I use a GWP of *anything* for methane, or for anything else?  Because you won't sit down and do the math yourself you have never been forced to understand what these terms actually mean and how they relate to each other.

In lieu of understanding it, you persist in this ugly behavior of just throwing out random stuff in the hope that something or other will stick. 

Here's the postmortem on what just happened. 

The reason for the difference in reported CO2eq between the source that you like (TJ Blasing/Someone-On-Wikipedia) and the source that you don't like (Ned/NOAA AGGI) has nothing whatsoever to do with how the individual forcings are calculated.  Nothing!

That difference is because NOAA AGGI (and I) are using the normal definition of CO2eq as an integrator of forcings from the set of well-mixed greenhouse gases ... but your Wikipedia Person inadvertently (?) added in tropospheric ozone, too, although it's quite different in various respects from the WMGHGs. 

That's why they got a different value of CO2eq.  Because they added in another gas into the mix, not because they calculated the forcings differently for the individual gases.

By the way, there's nothing wrong with that.  It's a bit awkward to use a non-standard definition for CO2eq, but it's fine. 

What tripped you up was that yet again you assumed that the difference between two values for CO2eq must mean that one of the sources must be calculating radiative forcing wrong. 

That's exactly what you did on the first page of this thread, when you were claiming that the fact that Wikipedia/Blasing's CO2eq was 100ppm higher than RCP 8.5's CO2eq proved that RCP 8.5 was badly underestimating radiative forcing.

Now you've done it again.  You claimed that the the fact that Wikipedia/Blasing's CO2eq was 35 ppm higher than Ned's/AGGI's CO2eq proved that Ned and AGGI are badly underestimating radiative forcing.

How many more times do you plan to make this mistake before you bother to actually look at how Wikipedia/Blasing is calculating their CO2eq?  You have endorsed it literally three times in various attempts to find fault with my methods, and you still do not understand it nor will you ever understand it until you do. the. math. for. yourself.
Title: Re: Comparison: forcings from CO2, CH4, N2O
Post by: TerryM on August 25, 2018, 09:59:40 PM
Ned W.
The DK is strong in this one, and you've exhibited truly Jobian patience.
Thanks


ASLR
Thanks for providing my first chuckle of the day with
"sidd
When you are wrong you like to double down." ;D




I think it's rather axiomatic that the best way to prevent future forcing is to cut back on present forcings, preferably using the most efficient methods.


Have fun guys
Learning lots, and enjoying all of it. 8)
Terry
Title: Re: Comparison: forcings from CO2, CH4, N2O
Post by: Ned W on August 25, 2018, 10:24:29 PM
I think it's rather axiomatic that the best way to prevent future forcing is to cut back on present forcings, preferably using the most efficient methods.

Thanks, Terry!  That's very concise, and something that probably everyone reading this can agree with.  Nothing wrong with stating things that are axiomatic. 
Title: Re: Comparison: forcings from CO2, CH4, N2O
Post by: AbruptSLR on August 26, 2018, 01:04:49 AM
In lieu of understanding it, you persist in this ugly behavior of just throwing out random stuff in the hope that something or other will stick. 

Ned W,

I must say that I do not find your postings too attractive either, as your thinking (and NOAA's calculations) are stuck in an AR4 gestalt.

Drew Shindell (co-chair of Chapter 8 of AR5) provides the linked PowerPoint to clarify the new AR5 gestalt with regard to radiative forcing.

Title: "Radiative Forcing in AR5" by Drew Shindell

http://climate.envsci.rutgers.edu/climdyn2013/IPCC/IPCC_WGI12-RadiativeForcing.pdf
&
http://www.climatechange2013.org/

The first attached image shows that using AR4 thinking (bars in pale green) the total effective radiative forcing is lower than when using AR5 thinking (solid black bar).

The second image addresses what qualifies as radiative forcing and why effective radiative forcing is essential to include the answer to 'What is Radiative Forcing?'

The third image illustrates the relationships between emissions and concentrations.

The four image illustrates that AR5 does not include methane aerosol interaction within the radiative forcing attributed to Aerosols and Precursors but rather in the radiative forcing due to CH4.
Title: Re: Comparison: forcings from CO2, CH4, N2O
Post by: sidd on August 26, 2018, 01:12:21 AM
"do. the. math. for. yourself."

Precisely. Those who will not learn arithmetic are doomed to talk nonsense.

sidd

Title: Re: Comparison: forcings from CO2, CH4, N2O
Post by: AbruptSLR on August 26, 2018, 01:19:56 AM
"do. the. math. for. yourself."

Precisely. Those who will not learn arithmetic are doomed to talk nonsense.

sidd

Your logic is a flawed as your conclusion
Title: Re: Comparison: forcings from CO2, CH4, N2O
Post by: TeaPotty on August 26, 2018, 01:26:59 AM
All this talk of “do the math” as a winning argument, and no math to prove their side. In fact, Ned hasn’t even posted an “I’m right because...”. All I see is passive aggressive attacks of AbruptSLR, appeals to authority, and outright dismissal of any information opposing his worldview. With a few simple google searches, it’s easy to see he’s wrong.

Even Ned admitted in this thread that he doesn’t know much of what he’s talking about, and then he acts all confident about his opinion. I bet Ned will also tell us 2C is still possible too, bc the IPCC said so, LOL.
Title: Re: Comparison: forcings from CO2, CH4, N2O
Post by: sidd on August 26, 2018, 02:58:56 AM
To return to substantiative discussion rather than a Gish Gallop through a magpie selection of random papers:

I reread the Etminan paper, and i find i had forgotten what a nice paper it is . Very clear, and gives nice formulae for CH4, N20 and CO2, but the real value is in the explanation of the calculation. The exposition of the importance of shortwave and overlap is excellent.

It mainly deals with RF but they have a para on the GWP

"The calculations of metrics (global warming potential (GWP) and global temperature change potential (GTP)) presented in Myhre et al. [2013a] are also impacted. These utilize radiative efficiencies (REs) for small perturbations around present‐day concentrations. For CO2 and N2O these are affected by about 1% or less compared to the values presented in Table 8.A1 of Myhre et al. [2013a]. By contrast, the CH4 radiative efficiency (RE), for small perturbations about present‐day concentrations, increases from 3.63 × 10^(−4) to 4.48 × 10^(−4) W /m^2/ppb, an increase of 23%. This percentage difference is slightly lower than for the industrial era CH4 change because differences in the updated expression relative to MHSS98 are largest for low CH4 concentrations (see Table S1). Since the GWP and GTP values for CH4 in Myhre et al. [2013a] include indirect effects due to ozone and stratospheric water vapor change, and the absolute contribution of these is unchanged by the increase in the RE, the metrics themselves increase by about 14%. The GWP for the 100 year time horizon, the most commonly used metric, increases from 28 to 32. "

Open access, read all about it: doi: 10.1002/2016GL071930

Now it's all very well to take a concentration vs time curve from the RCPs. But doing better, by say actually estimating concentration pathway of methane into the future given an emissions profile depends critically on the assumed lifetime of methane. Which in turn depends on the OH concentration and other factors.

How good are the atmospheric chemistry modules in the models, say something like CM3 or Mozart ?

sidd
Title: Re: Comparison: forcings from CO2, CH4, N2O
Post by: Ned W on August 26, 2018, 04:13:28 AM
Ned W,

I must say that I do not find your postings too attractive either, as your thinking (and NOAA's calculations) are stuck in an AR4 gestalt.

Drew Shindell (co-chair of Chapter 8 of AR5) provides the linked PowerPoint to clarify the new AR5 gestalt with regard to radiative forcing.

[snip]

The first attached image shows that using AR4 thinking (bars in pale green) the total effective radiative forcing is lower than when using AR5 thinking (solid black bar).

[snip]

The third image illustrates the relationships between emissions and concentrations.

Let's take the latter point first.  On  the slide in question, note the large black words "Both perspectives in AR4, both perspectives in AR5".  Right there, that ought to have told you that Shindell does not agree with your characterization of abundance-based forcing as obsolete "AR4 thinking" and emissions-based forcing as improved "AR5 thinking".

The slide before that one (not included in your post) helps explain this.  Shindell is explaining that emissions-based forcing is mostly of interest "for Policy Makers", and abundance-based forcing is mostly of interest "for Scientists".

This is exactly what I explained to you earlier.  These are two different ways of describing radiative forcings.  Neither one is "right" and neither one is "wrong".  Each has its own advantages.  Mostly, however, they are just designed to answer different questions!

Now, back to your first point.  You are quite right that the slide in question (taken from IPCC AR5 figure 8.16) shows that the forcings in AR4 were lower than the same forcings in AR5. 

Everything you concluded from that fact was wrong, though.

You assumed that  the difference is due to changes in how forcings are calculated, from an obsolete, wrong "AR4-thinking" method to a new and better "AR5-thinking" method. 

And you further assumed that this proves that all my calculations of forcing in this thread are wrong because they use the obsolete bad old "AR4-thinking".  I'm calculating stratospherically adjusted RF, not the fancy new ERF!  Get with it, Ned!

Except ... take a look at the page in AR5 before the one on which that figure is found.  On that page, look at Table 8.6:

(https://i.imgur.com/NcMIRz0.png)

The first row of the table is what we're talking about: radiative forcings for well-mixed greenhouse gases (CO2, CH4, N2O, and the fluoro/halocarbons).

The first four columns show the RF  (not ERF) values from IPCC AR2, AR3, AR4, and AR5.  The last column shows the ERF from AR5. 

There are several things here that you probably should consider:

(1) The AR5 ERF and AR5 RF values for WMGHGs are ... identical.  2.83 and 2.83.  I keep telling you this, and you keep ignoring it.  ERF vs RF matters a lot for some things, but the central tendency of the estimates for most of the greenhouse gases are very close in RF vs ERF.  In fact, in this case the uncertainty ranges differ, but the mean estimates are identical.

(2) The AR4 RF and AR5 RF are not identical.  In fact, the AR5 RF for well-mixed greenhouse gases (2.83) is clearly higher than the AR4 RF (2.63).  Is this, finally, proof of the existence of the "AR4-thinking" vs "AR5-thinking"? 

No!  It's just that AR4 came out six years before AR5 and the forcings increased because people kept emitting more CO2, CH4, and N2O!

Look at the next-to-last column in the table.  It explains why there is a difference between AR4's forcing and AR5's forcing:

Quote
Change due to increase in concentrations

Sure enough, if you look at NOAA AGGI, the total forcing from WMGHGs in 2005 and 2011 were 2.63 and 2.82 respectively -- effectively identical to the values from Table 8.6 in AR5.

So, to sum up:

* For the greenhouse gases that are the subject of this thread, AR5 shows that there is no significant difference between ERFs and RFs.  This is exactly what I have told you, repeatedly. 

* The estimates of greenhouse gas RF from me (and from NOAA AGGI) precisely match the RF estimates in both AR4 and AR5.  There is no such thing as "AR4-thinking" and "AR5-thinking" on this issue.

There is nothing wrong with my calculations.  When I use the IPCC's equations (as in this thread) they give the right answer, and when I use Etminan's equations (as I have elsewhere), those also give the right answer. 

You can accept this gracefully and move on.  Or you can keep doing what you're doing.  It's your choice.
Title: Re: Comparison: forcings from CO2, CH4, N2O
Post by: Ned W on August 26, 2018, 04:20:05 AM
To return to substantiative discussion rather than a Gish Gallop through a magpie selection of random papers:

I reread the Etminan paper, and i find i had forgotten what a nice paper it is . Very clear, and gives nice formulae for CH4, N20 and CO2, but the real value is in the explanation of the calculation. The exposition of the importance of shortwave and overlap is excellent.

Thank you for this.  Yes, Etminan 2016 is a beautiful paper.  One can learn so much from reading it, and from trying out the mathematics described therein.  And it's open access, too.  And there's a table in the supplemental information that contains lots of examples of forcing values for changes in concentration relative to 2011, which is very handy if you're trying to do this yourself and want to check your work.

Mainly, though, the value is (as you said) in the very clear explanations.  It really is one of my all-time favorite papers.

... and thanks also for your suggestion that we get this thread back on track.  It's been frustrating.  I started out trying to actually make comparisons, do "thought experiments", and experiment with real data.  Then it devolved into two pages of pointless arguing.  I should have known better than to get drawn into all that.

 :-\
Title: Re: Comparison: forcings from CO2, CH4, N2O
Post by: Rod on August 26, 2018, 04:28:32 AM
According to the second post in this thread, it was started by Ned W to address the following issue:

For some reason there's a disproportionate emphasis on methane here on ASIF.  It was very important in the past but over the next few decades it will be basically trivial in comparison to the warming from CO2.

The discussion has been very interesting, but I am getting the feeling that Ned W is playing the strawman game.  The concern that I have about methane, and the concern I have read from many here on the forum, is about potential positive feedbacks - which models do not include.

I appreciate the comments and citation to authorities offered by both Ned W and AbruptSLR.  I think they both weaken their credibility by personally attacking each other, but I appreciate their efforts in discussing the various model inputs. 

It is clear to me that although they disagree with each other, they are both very smart and have important information to add on this topic. 

However, the reason many people on the ASIF are concerned about potential methane emissions is because of research conducted by scientists like Shakhova and Katey Walter Anthony.  A-Team posted a nice image in post #14 that was created by Zack Labe showing the increasing trend in methane. 

Scientists don't know where those increases are coming from, so it is impossible to model them.  As I stated earlier in this thread, we can all agree CH4 is more powerful than CO2, molecule per molecule, as a GHG. 

We can also all agree that right now there is a lot less (almost one-thousand fold) CH4 in the atmosphere than CO2.  Finally, we know that the half life of CH4 is fairly short (although impossible to precisely predict) because of the presence of OH in the atmosphere. 

With that said, I turn back to the battle between Ned W and AbruptSLR.  You can not use current models to predict the effects of positive feedbacks on CH4 emissions, unless you believe those future feedbacks and emissions will be negligible. 

I don't think the people on this forum who are concerned about potential CH4 emissions believe they will be negligible, so fighting over model inputs does not in any way address the issue that Ned W stated in his second post as the purpose of this thread. 

I don't mind learning about the models by watching you two debate them, but I think you should stop taking things so personal.  It detracts from what you are trying to say. 

Ned W, if you really want to convince people that methane emissions will be "trivial" over the coming decades, then you need to do more than demonstrate your mathematical prowess regarding a model that does not even include the positive feedbacks about which people are concerned. 

Title: Re: Comparison: forcings from CO2, CH4, N2O
Post by: Pmt111500 on August 26, 2018, 05:40:41 AM
It's of course no surprise that by ignoring positive feedback from calculus you get no positive feedbacks in calculus results. But these sorts of positive feedbacks are not about the radiative equilibrium, it's more of a physical chemistry thing. I don't know much about how models work on these.
Title: Re: Comparison: forcings from CO2, CH4, N2O
Post by: sidd on August 26, 2018, 07:05:50 AM
Re: thought experiments

Here is analysis of fairly apocalyptic methane scenarios.

Lets's say the atmos-chem models are correct. And let us say for the moment, the suggestion of a 50 GTt burp is correct.  Then what is the impact ? Unsurprisingly Isaksen et al. have worked this out almost a decade ago using then (2010)  current atm-chem and ECMWF.  (They model a 50GT burp in one year as opposed to the decadal scale some have proposed.) They also work out effects of sustained emissions 2.5,4,7 and 13 times current emissions. These are giant perturbations, so unsurprisingly they find giant effects, including enhancement of methane lifetime as atmospheric concentration rises.

Read all about it.

doi:10.1029/2010GB003845

Copy at

https://darchive.mblwhoilibrary.org/bitstream/handle/1912/4553/2010GB003845.pdf?sequence=1

I am kinda skeptical that such large emissions of methane are possible. One big question is why didn't Eemian or Holsteinan trigger such release ?

I suspect that atm-chem has moved on since then, and so have the models. There are probably more recent papers along similar lines.

sidd



 
Title: Re: Comparison: forcings from CO2, CH4, N2O
Post by: kassy on August 26, 2018, 09:47:50 AM
The CO2 forcings were lower in those two periods? Unprecedented actions might well have unprecedented reactions?

https://en.wikipedia.org/wiki/File:Carbon_Dioxide_400kyr.png
Title: Re: Comparison: forcings from CO2, CH4, N2O
Post by: TerryM on August 26, 2018, 10:35:01 AM
I think it's rather axiomatic that the best way to prevent future forcing is to cut back on present forcings, preferably using the most efficient methods.

Thanks, Terry!  That's very concise, and something that probably everyone reading this can agree with.  Nothing wrong with stating things that are axiomatic.


I wax eloquent to express the obvious.
I wax skis to shush the moguls
I wax moles to enjoy the arcades.


But my mustache bristles indignantly at the indignity
Of ever being waxed in place - on my face  :P
Terry
Title: Re: Comparison: forcings from CO2, CH4, N2O
Post by: Pmt111500 on August 26, 2018, 01:17:08 PM
The CO2 forcings were lower in those two periods? Unprecedented actions might well have unprecedented reactions?

https://en.wikipedia.org/wiki/File:Carbon_Dioxide_400kyr.png
Holocene as a whole is also starting to be one of the longer interglacials.
Title: Re: Comparison: forcings from CO2, CH4, N2O
Post by: Ned W on August 26, 2018, 01:28:08 PM
I am kinda skeptical that such large emissions of methane are possible. One big question is why didn't Eemian or Holsteinan trigger such release ?

Yes.  The Eemian had extremely high summer-season solar forcing in the Arctic.  MIS-11 was so warm for so long that virtually all the land ice in Greenland melted.  But there's no evidence for a massive "methane bomb" in either one. 

The concern that I have about methane, and the concern I have read from many here on the forum, is about potential positive feedbacks - which models do not include.

I understand that many people here are concerned about such feedbacks. 

It's important to be clear about what the figures in this thread are showing.  They're not the output from hypothetical climate models that could be underestimating how much methane is being emitted from natural feedbacks.  They're just calculations of how much warming the actual methane (and CO2 and N2O) molecules within the atmosphere have caused, in the past and present.

Any feedback that is operating today is implicitly included. Obviously, future feedbacks that haven't kicked in yet, or that are undetectably small now but will become large in the future, aren't included. 

So methane that is being released from permafrost soils today is in fact included in this (well, not "today" since the observations I'm using are annual and don't include 2018 yet).

As for the Katey Walter Anthony paper, I did provide some analysis of their numbers on the first page of this thread.  Without looking back, my recollection is that the additional Arctic methane feedbacks over the rest of this century worked out to be about 0.9% of the total expected warming.  So it would increase the warming projected by IPCC AR5, but by a modest amount.  It's not a "methame bomb".

That said, it's one thing to argue that my analysis of the past and present is correct (so far as it goes) but doesn't adequately represent what will happen in the future. That's a fair argument to make, if people want to do so. But it's another thing to argue that the calculations I've been doing using past and current measurements are all wrong, particularly when the claimed reasons for that error are vague, shifting, and repeatedly debunked.  If nothing else, all the prior argument here has at least established that yes, the methods used for calcuating past and present forcing in this thread have been appropriate.

Also note that there are other threads (Arctic methane release!) that are better places to discuss the feedbacks you're talking about, the KWA paper, etc. This thread is really meant for quantitative analysis of the WMGHGs at the global scale.
Title: Re: Comparison: forcings from CO2, CH4, N2O
Post by: TeaPotty on August 26, 2018, 01:59:23 PM
Another word rant from Ned. I think this thread should just be locked. Ned claims methane is insignificant, and proceeds to lead everyone down a goose-chase.

For some reason there's a disproportionate emphasis on methane here on ASIF.  It was very important in the past but over the next few decades it will be basically trivial in comparison to the warming from CO2.

As I keep telling people, I have no particular background in this (economics/policy/mitigation issues).  Not that I think it's unimportant, I just don't want to speculate about something outside my area of comfort.
Title: Re: Comparison: forcings from CO2, CH4, N2O
Post by: Ned W on August 26, 2018, 02:11:23 PM
A reminder:

(https://i.imgur.com/GzUXHSZ.png)

Things may change in the future, but right now the impact of current methane concentration is relatively small compared to CO2.
Title: Re: Comparison: forcings from CO2, CH4, N2O
Post by: Ned W on August 26, 2018, 02:33:15 PM
That's right, TeaPotty.  I have no particular expertise in climate policy.  Which is why I'm posting about climate science in a topic area named "Science".
Title: Re: Comparison: forcings from CO2, CH4, N2O
Post by: TeaPotty on August 26, 2018, 02:39:42 PM
Nah Ned, you sound pretty clueless about the Science too.

https://www.epa.gov/climate-indicators/climate-change-indicators-climate-forcing
(https://i.imgur.com/7zmxCgd.png)

In this 2015 EPA graph, does CH4 look "trivial"?
Keep changing the topic of discussion Ned. This is how you win arguments, apparently.
Title: Re: Comparison: forcings from CO2, CH4, N2O
Post by: Ned W on August 26, 2018, 05:30:17 PM
Oren gave you the answer back in #92:

Posting in this very interesting thread is a major challenge due to the high scientific level of discussion. First of all, thank you Ned W for taking the time and the head-banging to clearly explain the concept of radiative forcing and its calculations, as opposed to the GWP concept.

I find myself thinking that, based on your numbers:

A. Current methane contribution to RF relative to 1750 is NOT insignificant, compared to CO2. Had there been no change in CH4 concentration at all since 1750, current RF would be much lower. You provided the numbers for this.

B. Current annual change of CH4 concentration is such that its RF annual change is small, while CO2 RF annual change is much larger. You provided the numbers for this.

Or, more simply:  methane forcing was increasing rapidly in the past (mid-20th century).  It is now increasing more slowly.  Perhaps in the future it will be faster.  But right now, the recent methane forcing is small compared to the recent CO2 forcing.

See also this graph posted earlier, which shows the rolling 30-year forcing in each year, 1800-present:

(https://i.imgur.com/lFdIZSi.png)
Title: Re: Comparison: forcings from CO2, CH4, N2O
Post by: AbruptSLR on August 26, 2018, 06:01:24 PM
One matter of fundamental importance is that AR5 is intended to give policymakers a better appreciation for how to tackle the problem of climate change than AR4 did.  In this regards AR5 provides guidance to policymakers that on an emissions basis the radiative forcing attributed to methane is very likely about twice that attributed to concentration increases (which was the focus of AR4):

Executive Summary of - Chapter 8: "Anthropogenic and Natural  Radiative Forcing",  In: Climate Change 2013: The Physical Science Basis. Contribution of Working Group I to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change

https://www.ipcc.ch/pdf/assessment-report/ar5/wg1/WG1AR5_Chapter08_FINAL.pdf

Extract: "Attributing forcing to emissions provides a more direct link from human activities to forcing. The RF attributed to methane emissions is very likely to be much larger (~1.0 W m–2) than that attributed to methane concentration increases (~0.5 W m–2) as concentration changes result from the partially offsetting impact of emissions of multiple species and subsequent chemical reactions."
Title: Re: Comparison: forcings from CO2, CH4, N2O
Post by: TeaPotty on August 26, 2018, 06:20:04 PM
Ned, it looks like ur cherry-picking to try to make a point that still makes little sense. And again your changing the subject. You specifically said CH4 will be trivial in coming decades, and u still have said a word that might validate this claim.
Title: Re: Comparison: forcings from CO2, CH4, N2O
Post by: gerontocrat on August 26, 2018, 07:32:33 PM
Nah Ned, you sound pretty clueless about the Science too.

In this 2015 EPA graph, does CH4 look "trivial"?
Keep changing the topic of discussion Ned. This is how you win arguments, apparently.

What a charmless post.

The graph quoted shows that for some years the increase in forcing from CH4 is very small compared with the increase in forcing from CO2.

Unless and until CH4 concentrations in the atmosphere significantly increase and unless and until increases in CO2 concentrations in the atmosphere significantly slow down or even turn -ve, this will continue.

This looks like yet another thread to leave well alone, lacking, as it does, a minimum level of politeness.
Title: Re: Comparison: forcings from CO2, CH4, N2O
Post by: Jim Pettit on August 26, 2018, 07:48:59 PM
Ned, it looks like ur cherry-picking to try to make a point that still makes little sense. And again your changing the subject. You specifically said CH4 will be trivial in coming decades, and u still have said a word that might validate this claim.

You know, it seems to me your comments here might be received in a better light were most not couched in ad hominems, screeds against established science and well-known scientists, sarcasm, vitriol, and lazy political bothsiderism. That is, you may be making some valid points about relative forcings--but I doubt those points are getting through to the mostly genteel, overwhelmingly knowledgable people here. There's nothing wrong with heated debate--that's how science works. But maybe try arguing your position with more facts and less troll-like behavior, whattaya say?
Title: Re: Comparison: forcings from CO2, CH4, N2O
Post by: Neven on August 26, 2018, 07:58:48 PM
Agreed, no need for this tone.
Title: Re: Comparison: forcings from CO2, CH4, N2O
Post by: TeaPotty on August 26, 2018, 08:06:55 PM
The graph quoted shows that for some years the increase in forcing from CH4 is very small compared with the increase in forcing from CO2.

A slower increase in the rate of forcing isnt the same as insignificant measure of total forcing, and present forcing is definitely not the same as future forcing amplified by expected feedbacks. Why are you comparing apples and oranges?

Unless and until CH4 concentrations in the atmosphere significantly increase

CH4 levels are definitely accelerating. And again, we have significant known and expected future feedbacks.

The whole point of this thread's argument is about Ned's claim that CH4 will be insignificant in future decades. And yet it keeps being sidelined, intentionally.

You know, it seems to me your comments here might be received in a better light

By whom? I have better things to do than be careful not to hurt fragile entitled egos.

screeds against established science and well-known scientists,

Which are all true, and based on research from scientists like Jim Hansen. Scientific Reticence and scientists "erring on the side of least drama" is established fact by now.

I doubt those points are getting through to the mostly genteel, overwhelmingly knowledgable people here.

I think anyone who knows wtf they're talking about wouldn't say something like "CH4 insignificant in future decades" and not provide any proof.

There's nothing wrong with heated debate--that's how science works. But maybe try arguing your position with more facts and less troll-like behavior, whattaya say?


Theres plenty of facts in this thread, and little debate. Moreso, I am an engineer. I dont belong to this silly polite culture of the academic world, and I thankfully never will. Truth deserves to be spoken, wrong behavior deserves to be called out.
Title: Re: Comparison: forcings from CO2, CH4, N2O
Post by: oren on August 26, 2018, 08:34:03 PM
Quote
The whole point of this thread's argument is about Ned's claim that CH4 will be insignificant in future decades.
I thought this thread quite useful and instructive in discussing various RFs. Perhaps Ned's point was that he believes methane's future contribution will be insignificant, but although I may think otherwise I don't find this was the whole of the discussion.
And TeaPotty, while you may not care what others think, you post in a public forum, so obviously you care enough to try and convince people of your viewpoint. Using personal attacks and ugly tones is not helping this goal.
This applies to a lesser degree to other posters in this thread. The debate is quite intetesting, the personal animosity off-putting.
Title: Re: Comparison: forcings from CO2, CH4, N2O
Post by: TeaPotty on August 26, 2018, 09:14:42 PM
although I may think otherwise I don't find this was the whole of the discussion.

Then you havent followed the discussion from page 1, where this whole argument began. You must have also missed all the attacks at AbruptSLR. As usual, conservatives are always the victims.
Title: Re: Comparison: forcings from CO2, CH4, N2O
Post by: GeoffBeacon on August 27, 2018, 02:27:57 PM
 I've just written "Cheating with temperature (http://www.brusselsblog.co.uk/cheating-with-temperature/)"  It argues that using temperature as a measure in the Paris Agreement was too vague. It should have specified limits to GHG emissions.

This is relevant to TeaPotty
Quote
The whole point of this thread's argument is about Ned's claim that CH4 will be insignificant in future decades.

Not all the bad things that are caused by climate change depend directly on temperature. For example sea level rise. In discussing the paper mentioned by AbruptSLR, Myles R. Allen et al. (2018) (https://www.nature.com/articles/s41612-018-0026-8) I say

Quote
One of the authors, Dr Michelle Cain, explains in a video about the paper (https://www.youtube.com/watch?v=HATNvcluCKE), that since methane has a lifetime of about 10 years it does not contribute much to long-term temperature rise and the goal of the Paris Agreement.

However, the temporary warming caused by methane will have gone somewhere: A higher surface temperature for a decade or so will cause some of the heat to be lost to space but some of the warming will have contributed to melting ice sheets and a much larger amount will have warmed the oceans, raising sea levels.

In Emission metrics and sea level rise (https://www.researchgate.net/publication/278401481_Emission_metrics_and_sea_level_rise), Sterner and Azar, discuss sea level rise caused by short-lived pollutants, such as methane. Their conclusions show that methane is many times worse than CO2 – for sea level rise even though it does not affect log-term surface temperatures greatly.

Quote
Perhaps the Small Island Developing States must agree with Myles Allen, who thinks methane emissions from current meat production is not much of a problem:

Quote
“We don’t actually need to give up eating meat to stabilise global temperatures,” says Professor Myles Allen who led the study (meat production is a major source of methane). “We just need to stop increasing our collective meat consumption.”

But the Small Island Developing States might worry about our meat consumption (especially beef and lamb) because it causes significant sea-level rise through enhanced methane emissions – although it doesn’t affect long term average global temperatures much.
 

And echoing TerryM's
Quote
I think it's rather axiomatic that the best way to prevent future forcing is to cut back on present forcings, preferably using the most efficient methods.

I worry that

Quote
short term heating can cause the feedbacks discussed in Lowe & Bernie’s paper (http://rsta.royalsocietypublishing.org/content/376/2119/20170263) mentioned below

Are there any papers that expand on "the worry that short term heating can cause feedbacks"?

Title: Re: Comparison: forcings from CO2, CH4, N2O
Post by: Richard Rathbone on August 27, 2018, 04:23:16 PM

Are there any papers that expand on "the worry that short term heating can cause feedbacks"?



If you haven't looked at Steffen et al, you should.  https://doi.org/10.1073/pnas.1810141115

You should also look at it carefully, I reckon the numbers in the paper aren't big enough to match the general feedback=doom theme.

Title: Re: Comparison: forcings from CO2, CH4, N2O
Post by: gerontocrat on August 27, 2018, 04:57:58 PM
I attach graphs using data from NOAA on how emissions - CO2, CH4 and other - have changed since 1979. The data supports the contention that at the moment the increase in CO2e is mainly coming from CO2 emissions derived mainly from human activity, and that CH4 emissions are increasing but somewhat slowly.

However, that is a very different question from what happens in the future. The plethora of studies in recent years on both methane and carbon stocks, e.g.s methane from shallow seas such as the ESAS, methane and carbon from thermokarst lakes, from tropical and boreal forest soils, from greening of the tundra, all suggest that perhaps sooner rather than later, increases in GHG emissions from climate feedbacks could overwhelm those from direct human activity.
Title: Re: Comparison: forcings from CO2, CH4, N2O
Post by: AbruptSLR on August 27, 2018, 05:07:18 PM
I've just written "Cheating with temperature"  It argues that using temperature as a measure in the Paris Agreement was too vague. It should have specified limits to GHG emissions.

Better still, imo, is basing targets on actual global ghg levels in the atmosphere. Why because that will capture both human and natural feedback emissions. These are the only numbers that really count. Not what humans calculate they have "emitted" - how much and how fast to drive down human emissions should be predicated on actual real world measurements and measurable accurate yardsticks. Not a popular idea. Because it makes govts much more accountable to real outcomes vs rubbery figures. That why the UNFCCC were happy to set it up the way it is now, imo.

AR5 explicitly states that: "Attributing forcing to emissions provides a more direct link from human activities to forcing."  Thus, while it is appropriate to also examine atmospheric concentrations, better policy can come from examining radiative forcing associated with emissions:

Executive Summary of - Chapter 8: "Anthropogenic and Natural  Radiative Forcing",  In: Climate Change 2013: The Physical Science Basis. Contribution of Working Group I to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change

https://www.ipcc.ch/pdf/assessment-report/ar5/wg1/WG1AR5_Chapter08_FINAL.pdf

Extract: "Attributing forcing to emissions provides a more direct link from human activities to forcing. The RF attributed to methane emissions is very likely to be much larger (~1.0 W m–2) than that attributed to methane concentration increases (~0.5 W m–2) as concentration changes result from the partially offsetting impact of emissions of multiple species and subsequent chemical reactions."
Title: Re: Comparison: forcings from CO2, CH4, N2O
Post by: AbruptSLR on August 27, 2018, 05:20:50 PM
As we are moving towards AR6, this thread would benefit from considering the SSP scenarios in addition to the RCP radiative forcing scenarios.  In this regards, the first attached image issued by the Global Carbon Project compares the SSP scenarios vs the observed projected thru 2017 for the fossil fuel and land use change CO2 emissions.  This plot indicates that we are currently following the SSP5 Baseline pathway, and not SSP3 which roughly represents the Paris Accord path forward.  This point is clarified by the second attached image where the authors of the Shared Socioeconomic Pathways, SSPs, label both SSP5 and SSP3 as baseline scenario depending on the decision maker's point of view.  However, I note that even SSP5 baseline can be taken to be optimistic as the third image indicates that SSP5 assumes a world population of about 8.5 billion by 2050; while the fourth image of the 2017 UN projection of global population gives a 50-50 chance that the world population will be 9.8 billion by 2050.  Thus taking SSP5/RCP 8.5 as BAU is fully supported by the IPCC process.
Title: Re: Comparison: forcings from CO2, CH4, N2O
Post by: AbruptSLR on August 27, 2018, 05:33:04 PM

However, the temporary warming caused by methane will have gone somewhere: A higher surface temperature for a decade or so will cause some of the heat to be lost to space but some of the warming will have contributed to melting ice sheets and a much larger amount will have warmed the oceans, raising sea levels.

In Emission metrics and sea level rise (https://www.researchgate.net/publication/278401481_Emission_metrics_and_sea_level_rise), Sterner and Azar, discuss sea level rise caused by short-lived pollutants, such as methane. Their conclusions show that methane is many times worse than CO2 – for sea level rise even though it does not affect log-term surface temperatures greatly.
[/quote]

With a hat tip to Richard Rathbone for a 2016 post in the Antarctic folder:

"At an EGU press conference DeConto said this work implied tipping points for major sea level rise occur between 2 and 2.7C above pre-industrial.

http://client.cntv.at/egu2016/press-conference-8 (DeConto starts about 22:10) "

While the entire video is worth watching I provide the four attached screenshots from the video.  The first two images are from the second (MIT EGU) speaker with:

(a) The first image showing the impact of the faux hiatus on both effective ECS (top panel) and effective oceanic diffusion (bottom panel), and the blue lines showing PDF values using observations until 2000 and the black lines showing PDF values using observations until 2010 (including part of the faux hiatus).  Further the lower panel clearly indicates that the faux hiatus (in GMST departures) was due to more heat content temporarily being sequestered into the oceans during the faux hiatus (some of which heat is now being released from the oceans).  Thus I believe that the blue line climate parameter distributions (with observations to 2000) is more "Realistic" (and indicates a mean ECS value of about 4C) and the black line climate parameter distributions is more "simplistic" (and is best ignored).

(b) The second image shows the implications of both MIT's more "Realistic" climate parameters (left panel, which is good to consider) and "simplistic" climate parameters (right panel, which is best ignored) for different carbon emission scenarios described in the video but with the current Paris pledges indicated by the red lines for which the more "Realistic" climate parameters indicate that we will reach 2C by about 2050 and 2.7C by about 2060.

The last two images are from the DeConto & Pollard EGU presentation with:

(c) The third image showing different carbon concentration pathways with the upper left panel showing the RCP scenarios used by DeConto & Pollard (2016) for their SLR projections; and the bottom left panel showing three new pathways postulated by DeConto where we follow the RCP 8.5 50%CL scenario until we reach 2C (by about 2040), 2.7C (by about 2065) and 3.6C (by about 2090), respectively for the blue, green and red lines.

(d) The fourth image shows DeConto & Pollard's (2016 EGU) projections of Antarctic contributions to changes in global mean sea level, GMSL, by the 2C (blue line), 2.7C (green line) and 3.6C (red line) forcing scenarios.  I believe that DeConto & Pollard's 2C scenario is not achievable in the real world (as confirmed by the second attached MIT analysis), and that by 2100 the 2.7C and the 3.6C forcing scenario produce essentially the same amount of increase in GMSL.  Taken together with the more "Realistic" MIT analysis the DeConto & Pollard (2016 EGU) findings indicate it likely that the WAIS collapse will begin about 2050 following the current Paris Pact pledges (and also ignoring the increase in carbon emissions associated with increasing agricultural growth).

Also, I note that the indicated DeConto & Pollard (2016 EGU) findings do not include Hansen et al (2016)'s ice-climate feedback, nor the current positive PDO phase, nor higher ECS values, nor the activation/acceleration of non-linear positive feedback mechanisms and thus errs on the side of least drama.
Title: Re: Comparison: forcings from CO2, CH4, N2O
Post by: AbruptSLR on August 27, 2018, 05:59:28 PM

Are there any papers that expand on "the worry that short term heating can cause feedbacks"?



If you haven't looked at Steffen et al, you should.  https://doi.org/10.1073/pnas.1810141115

You should also look at it carefully, I reckon the numbers in the paper aren't big enough to match the general feedback=doom theme.

It is my opinion that consensus climate scientists do not adequately account for the dynamical/periodic climate attractor associated with the on-going synergy between such Earth Systems as: the bipolar seesaw, ice-climate feedback, ENSO trends/cycles, cloud feedback, polar amplification Hadley cell expansion and precipitation patterns.  For example, an acceleration of ice mass loss from Jakobshavn thru 2028 would contribute to the North Atlantic cold spot (regardless of possible increased net snowfall on Greenland in this timeframe); which will serve to somewhat slow the MOC, which in turn will increase the absorption of heat by the tropical oceans, and thus will contribute somewhat to increased extreme ENSO events.

Also, Proistosescu & Huybers (2017), PH17, has demonstrated, using CMIP5 output, that a slow response feedback associated with the ocean heat content of the Tropical Pacific and the Southern Ocean has already been building since 1750 and is now contributing to ECS.  This can be seen directly in the first & second images, and indirectly in the middle panel of the third image (from Andrew's 2015 Ringberg presentation), and in the red 'time-dependence' curve of the forth image (which supports a mean ECS value of 4.5 when the considered time dependent feedbacks have kicked in) from Amour (2016).
Title: Re: Comparison: forcings from CO2, CH4, N2O
Post by: AbruptSLR on August 29, 2018, 07:16:06 PM
Focusing on atmospheric CO2 concentrations has led policymakers to assuming the use of negative emissions technology (generally BECCS) to their plans to meet the Paris Agreement goals.  However, the study cited in the linked article finds that extensive use of BECCS technology would most likely lead to an increase in carbon in the atmosphere rather than the decrease assumed by many IPCC projections:

Title: "Guest post: Why BECCS might not produce ‘negative’ emissions after all"

https://www.carbonbrief.org/guest-post-why-beccs-might-not-produce-negative-emissions-after-all

Extract: "In our new study, published in Nature Communications, my colleagues and I find that expansion of bioenergy in order to meet the 1.5C limit could cause net losses in carbon from the land surface. Instead, we find that protecting and expanding forests could be more effective options for meeting the Paris Agreement."

BECCS is also very expensive and can put major stains on land use as noted in the following linked article:

Title: "Guest post: Six key policy challenges to achieving ‘negative emissions’ with BECCS"

https://www.carbonbrief.org/guest-post-six-key-policy-challenges-to-achieving-negative-emissions-with-beccs

Extract: "Biomass energy with carbon capture and storage (BECCS) features as a key technology for delivering the Paris Agreement on climate change. It is included in many pathways developed using integrated assessment models (IAMs)."

Thus, it seems to me that with the limited will power that global policymakers seem to be able to muster, it seems advisable to be to spend our limited willpower to first restrict methane emissions and then to tackle the very real problem of carbon dioxide missions."

Edit: Regarding the limited collective willpower of policymaker I note that Australia recently announced its proposed plan to withdraw from the Paris Agreement.

https://www.independent.co.uk/news/world/australasia/australia-climate-change-malcolm-turnbull-prime-minister-leadership-a8499366.html
Title: Re: Comparison: forcings from CO2, CH4, N2O
Post by: Ned W on September 01, 2018, 02:52:46 AM
Before this thread wanders too far off, I'd like to tie up a few loose ends.

First, earlier I posted a comparison of the recent (2012-present) forcings from each of the major well-mixed greenhouse gases (WMGHGs), from each of the CMIP5 scenarios and also from observations (via NOAA AGGI).

Various objections were raised, but each of them has been laid to rest:


OK, with all that out of the way.  There is one improvement that could be made, which is to update the forcing calculations based on Etminan et al. 2016.  I did this for the graphs on the first page of the thread, but not for this latter one. 

So here's the most up-to-date comparison:

(https://i.imgur.com/FVk2IZZ.png)

As with the earlier version of this graph, it appears that RCP 8.5 has been overestimating the CH4 (and CO2) forcings, while the other scenarios have been underestimating them.

The CH4-to-CO2 ratio is 0.11 for the observations (i.e., CH4 forcing is "currently" about 11% as large as CO2 forcing).  Upon further reflection I think describing this as "fairly small" would be reasonable, but the phrase I used in the second post of this thread ("basically trivial") is not appropriate.  CH4 forcing is "small" but not "trivial" compared to CO2, and it will probably grow in the future.

On that note, in case anyone is curious, here is what the CMIP5 scenarios show for the next three decades:

(https://i.imgur.com/mU1QRJ9.png)

Obviously, there are no observations for the future (yet).  If the real world ends up somewhere between RCP 4.5 and 8.5 (as it is now) that would mean the CH4:CO2 ratio would be somewhere between 0.01 and 0.22 -- a pretty wide range of possibilities. 

It's important to keep in mind that the CMIP5 scenarios are simply "concentration pathways" not process models. The committee picked one case that has very high concentrations (8.5) and then some others with differing combinations of lower concentrations (the others).

What this means is that it's not appropriate to, say, take the results of a new paper (e.g., the Katy Walter Anthony one) and somehow "add" it to RCP 8.5, on the assumption that RCP 8.5 contained a distinct set of processes and the KWA one is a new, additional one that needs to be added in.  That is not how the RCPs work.

Having said that, I would remind us all that as a rough comparison, the increase in forcing from CH4 emissions from thermokarst lakes according to the KWA paper works out to (roughly) 1% of the total forcing (for the same time period) under RCP 8.5 (see the first page of this thread for details).  CO2 forcing from thermokarsts adds a little more, but the total effect is still small.  Keep in mind, everyone, that just as the CH4 forcing is fairly small compared to the CO2 forcing globally, the Arctic CH4 forcing is fairly small compared to the global CH4 forcing.

Thanks for your patience (if anyone bothered to make it through all those words).
Title: Re: Comparison: forcings from CO2, CH4, N2O
Post by: sidd on September 01, 2018, 04:44:43 AM
Thaks for doing the Etminan calcs.

sidd
Title: Re: Comparison: forcings from CO2, CH4, N2O
Post by: oren on September 01, 2018, 11:59:18 AM
Thank you Ned for the summary.
I will just add that I dislike the wording used in the last post.
In my layman view, forcing is how much the Earth's energy balance is out of equilibrium - this is what drives AGW, and added forcing is how much this out-of-balance situation is changing over time - this accelerates AGW. I understand that in the scientific terminology the change in forcing is also called forcing. But a layman would be confused by it.
So IMHO, the 2012-2017 RF chart is showing something interesting - that CO2 is the accelerator of AGW. BUT - it is also hiding something that shouldn't be hidden - that current abundance of CH4 does have a siginificant contribution to AGW, and that reducing this abundance would slow down AGW. CH4's short residence time in the atmosphere makes this an important point, that I think should be mentioned when you summarize the subject, especially after a few people felt that the discussion was minimizing CH4.
If I were to light a huge lamp pointed at the earth, its climate forcing would be huge, but in your charts it would be zero as there is no annual change. IMHO, not properly presented.
IMHO, your summary should also show RF 2017-1750.
Title: Re: Comparison: forcings from CO2, CH4, N2O
Post by: Ned W on September 01, 2018, 12:58:27 PM
Thanks, Oren, for your comments.  I think most of what you're saying here basically can be summarized as "answers to a different question".

In my layman view, forcing is how much the Earth's energy balance is out of equilibrium - this is what drives AGW, and added forcing is how much this out-of-balance situation is changing over time - this accelerates AGW.

One problem with that is that the Earth doesn't have a single "equilibrium".  When there is an externally forced change -- people add CO2, the sun gets brighter, whatever -- the system slowly adjusts to compensate for it, until the Earth reaches a new equilibrium at a higher (or lower) temperature.
 
Quote
I understand that in the scientific terminology the change in forcing is also called forcing. But a layman would be confused by it.

There is no difference between what you are calling a "forcing" and a "change in forcing".   A forcing is simply the difference in the Earth's radiative climate between two different sets of conditions. Those conditions can be further apart or more similar, whatever you are trying to compare.

I believe that a large number of people here on ASIF have trouble with that idea, at a gut level.  This exact same thing came up one year ago this week, when Jai Mitchell was angry at me for talking about forcing using something other than 1750 as the baseline (https://forum.arctic-sea-ice.net/index.php/topic,445.msg126913.html#msg126913).

The change in radiative balance from CO2=280ppm to CO2=410ppm conditions is a forcing.  The change from 400 to 410 conditions is also a forcing.  There is no difference at all conceptually, just one is bigger than the other.

So ... I understand what you are describing as the "layman's" concept of forcing.  But it's not how scientists use forcing.  And if we are going to be using data from scientists and talking about papers written by scientists, it's probably a good idea to start using the terms the way they do.

Quote
So IMHO, the 2012-2017 RF chart is showing something interesting - that CO2 is the accelerator of AGW. BUT - it is also hiding something that shouldn't be hidden - that current abundance of CH4 does have a siginificant contribution to AGW, and that reducing this abundance would slow down AGW.

I understand the point you're trying to make.  I just think it is an answer to a different question ("how could we efficiently reduce or reverse warming in the future?"). 

Yes, we could reduce atmospheric methane in the future and create a negative forcing.  But the fact that we aren't doing so right now doesn't make it a positive forcing at the present time. 

There are a vast (infinite?) number of things we could do in the future to force the climate one way or another.  But we don't count "not doing X" as creating an anti-X forcing. 

Circa 2000ish, human emissions of CH4 plus natural feedbacks were in a relatively "steady state" where each year's emissions exactly compensated for each year's natural breakdown of prior emissions.  Adding more would create a positive forcing, reducing it would create a negative forcing.  Staying the same ... represents zero forcing.

Quote
CH4's short residence time in the atmosphere makes this an important point, that I think should be mentioned when you summarize the subject, especially after a few people felt that the discussion was minimizing CH4.

I think that's a different point, one that is of great relevance to the question of how to "undo" the warming we've done or avoid crossing some future threshold.  It's not directly relevant to the question of what's responsible for current warming.

As an example: I am not recommending this, but assume for the sake of argument that we could reduce the temperature by manufacturing a large volume of styrofoam pellets and covering the ocean with them, to reduce its albedo.  I wouldn't say that the fact that we aren't doing that means that there is currently a large positive styrofoam-pellet forcing because we could undo part of the past warming by dumping pellets in the ocean.  The fact that X offers an opportunity to create a negative forcing in the future doesn't mean it's creating a positive forcing in the present.

Quote
If I were to light a huge lamp pointed at the earth, its climate forcing would be huge, but in your charts it would be zero as there is no annual change.

It would show a huge forcing if you calculated forcing from time=0 to time=1.  If you waited a bit and then calculated forcing between two points in time with the lamp on at both times, it would show no forcing from the lamp.  Which is ... a realistic representation of what's happening, right?  Once the lamp is on and staying on, it's no longer forcing a change in climate.  That change is now in the past. 

It's true that at that point you could create a new, negative "lamp forcing" by turning off the lamp and cooling the planet.  But you could also create a new, positive "lamp forcing" by adding a second lamp.  Leaving things as they are just means ... no forcing.

Quote
IMHO, your summary should also show RF 2017-1750.

That's an answer to the question "What impact has the change of emissions since 1750 had on the Earth's climate?" 

Which is a fine question. The IPCC addresses that question, so they show that chart in every AR, in multiple forms.  It's just not the same question I'm asking (and answering) here.
Title: Re: Comparison: forcings from CO2, CH4, N2O
Post by: Ned W on September 01, 2018, 04:02:42 PM
FWIW, the initial version of my reply to Oren was extremely long and wordy.   So naturally I edited it to make it even longer and wordier. 

And having done that, I want to just pull out one more snippet to comment on.  The previous reply is about "science" while this part is about, I dunno, psychology?  Culture?

Quote
especially after a few people felt that the discussion was minimizing CH4.

From my perspective, there is a weird "local culture" thing here on ASIF where methane is held in particular respect, and anything that feels critical of methane ... sort of offends people.  To an outsider it almost feels kind of Trumpian -- if methane is important it needs to be THE BIGGEST! and if you say anything that makes methane seem "not big" then you're dissing methane.

So in my case, for example, I believe in AGW.  I agree that methane forcing was big in the past (the mid-20th century) and agree that it might be big again in the future.

But that's not enough.  If I add "But right now, methane forcing is pretty low compared to CO2, and I think it will take a couple decades for that to turn around" people start yelling and throwing stuff. 

I don't know why this is.  Methane is just part of the AGW problem and Arctic methane is just a smaller part of the methane part.  But it's kind of the "local hero" here and people don't take kindly to anyone disrespecting it.
Title: Re: Comparison: forcings from CO2, CH4, N2O
Post by: sidd on September 01, 2018, 09:07:56 PM
Re: "people start yelling and throwing stuff.  "

Use the ignore setting.

sidd
Title: Re: Comparison: forcings from CO2, CH4, N2O
Post by: AbruptSLR on September 01, 2018, 11:24:45 PM
The attached image makes it clear that thru 2017 the net CO2 emissions matched the Rapid Growth rate scenario SSP5 being used in CMIP6.  One would think that if policymakers took CO2 emissions seriously we would not be tracking the highest GHG emissions scenario in CMIP6.

Edit, the image is taken from:

http://folk.uio.no/roberan/GCP2017.shtml
Title: Re: Comparison: forcings from CO2, CH4, N2O
Post by: oren on September 02, 2018, 12:25:39 AM
Quote
It would show a huge forcing if you calculated forcing from time=0 to time=1.  If you waited a bit and then calculated forcing between two points in time with the lamp on at both times, it would show no forcing from the lamp.  Which is ... a realistic representation of what's happening, right?  Once the lamp is on and staying on, it's no longer forcing a change in climate.  That change is now in the past.
Ned, I have followed your explanations dilligently throughout this thread, but here I strongly beg to differ, both regarding CH4 and my hypothetical lamp. The Earth system has great inertia and a slow response time. A new large forcing appearing today, even were it to remain constant, would affect the climate for decades or even centuries, until the climate reached a new equilibrium.
When I see how dismissive you are of this hypothetical new lamp, I understand how thinking only in terms of delta-RF from year to year might blind someone to the effects of unchanging but above-equilibrium RF that continues for a long time. Yes the actual forcing will get smaller over time as the Earth warms in response, and yes it will be difficult to calculate the warming effect, but to say it doesn't matter because the RF is constant and therefore this year's RF is zero strikes me as very unscientific. IMHO 1750-present does matter a whole lot, unless you claim the Earth is in current equilibrium with the 1750-2016 RF, which I am certain it is not despite being unable to calculate it with any precision.
Title: Re: Comparison: forcings from CO2, CH4, N2O
Post by: AbruptSLR on September 02, 2018, 12:30:13 AM
It should be noted that both NOAA's and Ned W's radiative forcing calculations follow UNFCCC reporting procedures.  Furthermore, the first linked reference makes it clear that when following such UNFCCC reporting procedures result in the projection of a decline in global temperatures after achieving and maintaining a net-zero CO₂-equivalent emissions condition.  However, when using the GWP* procedure presented in the second linked reference, once the same net-zero CO₂-equivalent emissions conditions is reached and maintained global temperatures are projected to remain approximately constant (instead of declining):

J. Fuglestvedt, J. Rogelj, R. J. Millar, M. Allen, O. Boucher, M. Cain, P. M. Forster, E. Kriegler, and D. Shindell (2018 May 13), " Implications of possible interpretations of ‘greenhouse gas balance’ in the Paris Agreement", Philos Trans A Math Phys Eng Sci.; 376(2119): 20160445, doi:  10.1098/rsta.2016.0445

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5897819/

Extract: "For example, achieving and maintaining net-zero CO2-equivalent emissions calculated with GWP100—adopted for the implementation of the Kyoto Protocol and in UNFCCC reporting—would result in a peak and decline in global temperature and a cooling effect, with the rate of cooling dependent on the contribution of SLCFs to the overall CO2-equivalent emissions. Adopting a different usage of this metric, here denoted by GWP*, would result in global temperatures remaining approximately constant once net-zero CO2-equivalent emissions are achieved and maintained. Policymakers should be aware of these particularities and determine which metric is most appropriate in the context of the goals of the Paris Agreement."

&

Myles R. Allen et al. (2018), "A solution to the misrepresentations of CO2-equivalent emissions of short-lived climate pollutants under ambitious mitigation", npj Climate and Atmospheric Science 1, Article No. 16; Doi: https://doi.org/10.1038/s41612-018-0026-8

https://www.nature.com/articles/s41612-018-0026-8

Extract: "While cumulative carbon dioxide (CO₂) emissions dominate anthropogenic warming over centuries, temperatures over the coming decades are also strongly affected by short-lived climate pollutants (SLCPs), complicating the estimation of cumulative emission budgets for ambitious mitigation goals.  Using conventional Global Warming Potentials (GWPs) to convert SLCPs to "CO₂-equivalent" emission misrepresents their impact on global temperature."
Title: Re: Comparison: forcings from CO2, CH4, N2O
Post by: Ned W on September 02, 2018, 01:56:27 AM
The attached image makes it clear that thru 2017 the net CO2 emissions matched the Rapid Growth rate scenario SSP5 being used in CMIP6.  One would think that if policymakers took CO2 emissions seriously we would not be tracking the highest GHG emissions scenario in CMIP6.

Edit, the image is taken from:

http://folk.uio.no/roberan/GCP2017.shtml

"The attached image makes it clear"?  Here's an enlargement:

(https://i.imgur.com/OyFgzCm.png)

Note that for each of the SSP families (1-5) there are multiple pathways.  I believe the three ones that appear to be closest to the actual emissions from 2017 include one pathway from SSP5, one from SSP3, and one from SSP2. 

In any case, I don't think the graph you posted shows what you're saying it shows.  Maybe I'm wrong, though.  What do you see in the graph?
Title: Re: Comparison: forcings from CO2, CH4, N2O
Post by: Ned W on September 02, 2018, 02:47:38 AM
Quote
It would show a huge forcing if you calculated forcing from time=0 to time=1.  If you waited a bit and then calculated forcing between two points in time with the lamp on at both times, it would show no forcing from the lamp.  Which is ... a realistic representation of what's happening, right?  Once the lamp is on and staying on, it's no longer forcing a change in climate.  That change is now in the past.
Ned, I have followed your explanations dilligently throughout this thread,

Thanks!

Quote
but here I strongly beg to differ, both regarding CH4 and my hypothetical lamp. The Earth system has great inertia and a slow response time. A new large forcing appearing today, even were it to remain constant, would affect the climate for decades or even centuries, until the climate reached a new equilibrium.

Yes, of course.  You are referring to "warming in the pipeline", if I understand what you're saying.

But that doesn't affect the initial forcing.  It's a function of the climate sensitivity, which translates the forcing into a change in temperature.  That temperature change is spread out over a long period of time.

In your lamp case, here's how I see that working out:

(1) Turning the lamp on produces a basically instantaneous increase in incoming radiation.

(2) This creates a sudden positive climate forcing.

(3) Once the lamp is on, assuming its output is constant, there is no further "lamp forcing".  Its direct radiative input to the climate system is now fixed and unchanging.

(4)  Temperature responds much more slowly.  Over the next decade or so the planet warms up relatively fast, then the rate of warming tapers off, until at some point (a century or more) it is gradually approaching some kind of equilibrium state, with the planet at a higher temperature than before the lamp was turned on.

So in terms of temperature, each year is slowly increasing.  In terms of forcing, there is a large forcing when calculating it from before the lamp turns on to after it turns on, but lamp-forcing over any time interval that doesn't include turning the lamp on is 0.

That's the simple version.  There are of course complications:

(5) As the planet warms up, various positive feedbacks might cause the release of CO2 (e.g., from a warming ocean), CH4, etc.  That will cause the atmospheric concentrations of those gases to increase slowly during the century after the lamp is turned on.  As we measure the concentrations of those gases increasing in the atmosphere, we would describe them as being additional CO2-forcings and CH4-forcings, even though they're originating from feedbacks that were originally triggered by the lamp-forcing.

Pursing that further will cause this to veer into discussion of abundance- vs emission-based forcings, ERFs vs RFs, etc.  One reason that climate scientists will stick with the straightforward version of this -- even though it attributes some of the downstream effects of the initial lamp-forcing to an apparent CO2-forcing and CH4-forcing over the following years -- is because disentangling the very long term effects of the various forcings and attributing them to their original causes can only be done using climate models, and that in turn raises all kinds of problematic methodological issues.

In the real world, there are usually multiple forcings happening simultaneously (Milankovich, solar, volcanic, anthro CO2, anthro CH4, anthro N2O, etc.).  It's a lot more complicated than the lamp case.

Quote
When I see how dismissive you are of this hypothetical new lamp,

Dismissive?  Au contraire, I like it.

Quote
I understand how thinking only in terms of delta-RF from year to year might blind someone to the effects of unchanging but above-equilibrium RF that continues for a long time.

I would gently encourage you to drop the entire concept of "delta-RF" because it seems to be unhelpful.  Every RF is a delta.

"unchanging but [positive] RF that continues for a long time" -- This is extremely tricky to talk about, which is why I try so hard to get people to be clear in their language. 

What you mean by "unchanging but positive RF" is that you are continuously calculating RF relative to time 0, before the lamp turns on.  If we think of the lamp as providing 1 W/m2 at the planet, then this would mean that every time you measure it, forcing is 1 (relative to time 0).

But every time that you do that calculation, that "1 W/m2" is just telling you what the initial effect of turning on the lamp was.  All the actual change in the lamp's radiative input occurred at the start of the time period.  Nothing further is happening.

Mathematically, physically, and in every sense except perhaps layman-linguistically, this is identical to, e.g., calculating decadal forcings -- which would be 1 W/m2 in the first decade and then 0 in every subsequent decade.

Those are, literally, exactly the same thing.  The issue of "warming in the pipeline" or "equilibrium climate sensitivity" has nothing to do with the (nonexistent) distinction between these two ways of measuring forcing. 

Quote
Yes the actual forcing will get smaller over time as the Earth warms in response, and yes it will be difficult to calculate the warming effect, but to say it doesn't matter because the RF is constant and therefore this year's RF is zero strikes me as very unscientific.

That's very much not what I've been saying.  Or it's a mix of bits I would agree with and bits that I wouldn't.  Hopefully some of the above makes this clear, but if not ... it won't be easy to be clearer.

Quote
IMHO 1750-present does matter a whole lot, unless you claim the Earth is in current equilibrium with the 1750-2016 RF, which I am certain it is not despite being unable to calculate it with any precision.

I never said the Earth is in equilibrium (I think, and I certainly never would have said that intentionally). 

There is a distinction between the concept of "forcing" and the concept of "warming".  They are connected by climate sensitivity.  Warming results from forcing, and it plays out over a long period of time. 

So past history matters in terms of how much warming is happening now -- it's caused not just by current forcings, but by past ones too.  But here we're talking about warming (in kelvins) not radiative forcings (in watts per square meter).
Title: Re: Comparison: forcings from CO2, CH4, N2O
Post by: AbruptSLR on September 02, 2018, 02:55:09 AM
What do you see in the graph?

Your enlargement makes it clear to me that at the end of 2017 our path was closest to SSP5.  If you do not see that, look again.
Title: Re: Comparison: forcings from CO2, CH4, N2O
Post by: Ned W on September 02, 2018, 03:05:35 AM
What do you see in the graph?

Your enlargement makes it clear to me that at the end of 2017 our path was closest to SSP5.  If you do not see that, look again.

Actually -- the enlargement I posted is not from the same slide as the one you posted.  In the one you posted ... all the lines are from SSP5.  So I'm not sure how looking at it is supposed to show that 2017 is "closest to SSP5".  They're all SSP5.

In the graph I posted, all the cases are shown ... but the colors don't reflect which SSP group (1,2,3,4,5) they are, the colors reflect which case within a given group (2.6, 4.5, etc.) they are.

The point is, when you show all the cases, and not just the SSP5 ones, 2017 appears to be more or less in the middle of the pack.  And if you download the actual SSP emissions data, and go through the painfully complicated process of trying to compare observations to them ... 2017 is basically undistinguishable from a bunch of cases, some of which are from SSP5 but others from SSP2 and SSP3.
Title: Re: Comparison: forcings from CO2, CH4, N2O
Post by: AbruptSLR on September 02, 2018, 03:36:42 AM
What do you see in the graph?

Your enlargement makes it clear to me that at the end of 2017 our path was closest to SSP5.  If you do not see that, look again.

Actually -- the enlargement I posted is not from the same slide as the one you posted.  In the one you posted ... all the lines are from SSP5.  So I'm not sure how looking at it is supposed to show that 2017 is "closest to SSP5".  They're all SSP5.

In the graph I posted, all the cases are shown ... but the colors don't reflect which SSP group (1,2,3,4,5) they are, the colors reflect which case within a given group (2.6, 4.5, etc.) they are.

The point is, when you show all the cases, and not just the SSP5 ones, 2017 appears to be more or less in the middle of the pack.  And if you download the actual SSP emissions data, and go through the painfully complicated process of trying to compare observations to them ... 2017 is basically undistinguishable from a bunch of cases, some of which are from SSP5 but others from SSP2 and SSP3.
I know very well where your enlargement came from.  If you don't think that the CO2 emissions at the end of 2017 was closest to SSP5 you can look at the data at the following link:

http://sedac.ipcc-data.org/ddc/ar5_scenario_process/parallel_nat_scen.html

Plus, it is silly to make a big deal about the emissions at the end of 2017 being close to the center of the scenarios as IPCC keeps re-zeroing each new family of curves each time they are released.  If I am allowed to re-zero all the time, all of my projections will be very close a short time later.
Title: Re: Comparison: forcings from CO2, CH4, N2O
Post by: Ned W on September 02, 2018, 03:53:53 AM
I know very well where your enlargement came from.  If you don't think that the CO2 emissions at the end of 2017 was closest to SSP5 you can look at the data at the following link:

http://sedac.ipcc-data.org/ddc/ar5_scenario_process/parallel_nat_scen.html

Great, if it's that easy, why don't you give us the numbers for 2017?  Actual emissions, and, say, the three SSP/RCP pathway combinations that are closest to it?

Quote
Plus, it is silly to make a big deal about the emissions at the end of 2017 being close to the center of the scenarios as IPCC keeps re-zeroing each new family of curves each time they are released.  If I am allowed to re-zero all the time, all of my projections will be very close a short time later.

I am not sure what you mean by "re-zeroing" the SSP emissions values, but it doesn't really matter.  If you think the comparison is silly, why did you do it?  This was your comparison, not mine...
Title: Re: Comparison: forcings from CO2, CH4, N2O
Post by: AbruptSLR on September 02, 2018, 04:29:53 AM
I am not sure what you mean by "re-zeroing" the SSP emissions values, but it doesn't really matter.  If you think the comparison is silly, why did you do it?  This was your comparison, not mine...

I have my doubts that you are a scientist, so I am testing you.
Title: Re: Comparison: forcings from CO2, CH4, N2O
Post by: oren on September 02, 2018, 12:56:19 PM
Ned, thanks again for the detailed response. I completely understand your clear explanations about RF etc., so please don't feel as if you wasted words or anything.
I also realize that the relation of RF to climate policy is far from straightforward, and that when discussing RF it is very important to choose the proper range of years for the problem at hand.
With that, I will let this thread be so as to minimize ASIF suffering...
Title: Re: Comparison: forcings from CO2, CH4, N2O
Post by: magnamentis on September 02, 2018, 01:13:03 PM

I have my doubts that you are a scientist, so I am testing you.

so you're saying once more that it does not really matter what is true or makes sense but to be a scientist is what counts.

are you aware that you scientists need all the rest of humans who are not scientist do change things to the better?

if you understand that (i'm sure you do ;) ) then you should also consider that for many non-scientists it makes a not so good impression if scientists consider themselves as an elite club who disregard and try to deny anything that comes from non-scientists or scientist from other fields of expertise, only because they don't belong to their group.

this group dynamics are vastly responsible for most if not everything that went and goes wrong in human history.

the analysis of human behaviour is another science than the one about climate and weather but believe me, the impact of human behaviour is root cause while climate change is only on of the many negative effects from it.

however, to cut this short, only what is said and after that only what is done counts, not the background while of course the correct background increases chances to see things well.

we should all keep in mind that many brake-through finds and even more so most of the base brake through finds in maths, geometry, astronomy and philosophy have been made by self-educated observers, inventors or whichever terms applies best here.

there were no universities that taught geometry to Pythagoras. yes i know, examples always limp but for those who are open for considerations it's mostly clear what is meant.

even jesus (or the bible) is full of parables which are often abusend and or ridiculed, depending what the goal of the opponents are, while in fact the goal of the story is to teach ethics. (not moral)

however this exchange between you two is one of the most interesting ones i enjoyed for long, despite a few words like "silly" and the likes that, once absent, would make it even more pleasant ;)

Even though i can't tell who is a scientist and who is not, i find what Mr. Ned W has to say at least conclusive and profound and i admire his patience, would be happy to get a share :-D
Title: Re: Comparison: forcings from CO2, CH4, N2O
Post by: Ned W on September 02, 2018, 01:20:41 PM
Ned, thanks again for the detailed response. I completely understand your clear explanations about RF etc., so please don't feel as if you wasted words or anything.
I also realize that the relation of RF to climate policy is far from straightforward, and that when discussing RF it is very important to choose the proper range of years for the problem at hand.
With that, I will let this thread be so as to minimize ASIF suffering...

Thanks, Oren.  I really appreciated your comments in this thread, as with pretty much all of your comments elsewhere on ASIF.

Even though i can't tell who is a scientist and who is not, i find what Mr. Ned W has to say at least conclusive and profound and i admire his patience, would be happy to get a share :-D

Thank you for the kind words, magnamentis.  I think your patience is in better shape than mine, but I will work on it.
Title: Re: Comparison: forcings from CO2, CH4, N2O
Post by: AbruptSLR on September 02, 2018, 05:18:33 PM
are you aware that you scientists need all the rest of humans who are not scientist do change things to the better?

First, I am an engineer and not a scientist.

Second, you, Ned and everyone else on this forum are welcome to express your opinions, so long as I am welcome to express my opinions.

Regards
Title: Re: Comparison: forcings from CO2, CH4, N2O
Post by: TerryM on September 02, 2018, 10:52:02 PM
Opinions expressed as opinions are good. When opinions are expressed as facts they should be exposed, hopefully by someone with the patience and persistence of Ned.


I for one am delighted to have learned a little bit more about separating the wheat from the chaff.
Terry
Title: Re: Comparison: forcings from CO2, CH4, N2O
Post by: Rod on September 03, 2018, 01:19:54 AM
are you aware that you scientists need all the rest of humans who are not scientist do change things to the better?

First, I am an engineer and not a scientist.

Second, you, Ned and everyone else on this forum are welcome to express your opinions, so long as I am welcome to express my opinions.

Regards

I very much enjoy seeing your opinions AbruptSLR.  Please don't stop posting them. 

Magnamentis has expressed several times his opinions about scientists.  I enjoy reading what magnamentis has to say.   However, as someone who works in the environmental field and deals with experts almost everyday, I don't give his opinions much weight when he tries to downplay the opinions of real scientists.   When he attacked Fish the other day it really bothered me but I kept my mouth shut.

The first thing I always want to know about an expert is his/her formal education.  People can google key words all day long, but nothing beats a good education. 

Additionally, he is full of it when he says that "the rest of humans" have a say.  The courts and the administrative agencies set policy.  They would never accept an opinion from someone who was not qualified by education or experience to give that opinion. 

It would be nice if the rest of humans had a say, but they don't care.  They do what the law tells them to do, and the laws are made by the courts and administrative agencies. I know a little bit about this because it is what I do for a living. 

I should clarify I'm talking about how things work in the US. Things might be different in other parts of the world, but I doubt it.  It is also helpful for all of you Trump haters (I'm not a fan either) to know that even though he is president, he can not directly make policy for environmental laws.  He can appoint people that support his beliefs, but the rules they make still have to be approved by the courts and/or administrative agencies.
Title: Re: Comparison: forcings from CO2, CH4, N2O
Post by: AbruptSLR on September 03, 2018, 03:47:39 AM
I very much enjoy seeing your opinions AbruptSLR.  Please don't stop posting them. 

...snip …

The first thing I always want to know about an expert is his/her formal education.

Rod,

Thank you for your thoughtful words.  Good judgement requires hard work to develop and constant effort to maintain.

Personally, I have been impressed by James Hansen's good judgement; and hopefully policymakers will take his advice to heart before it is too late to avoid too severe of consequences.

In this vain of thought I remain readers that AR5 Chapter 8 advises policymakers that the radiative forcing, RF, attributed to methane emissions is more than twice the RF attributed to increases in methane concentration:

Extract from AR5: "The RF attributed to methane emissions is very likely to be much larger (~1.0 W m–2) than that attributed to methane concentration increases (~0.5 W m–2) as concentration changes result from the partially offsetting impact of emissions of multiple species and subsequent chemical reactions."

Edit, for your information I have a  BS, MEng & PhD all from UC Berkeley.
Title: Re: Comparison: forcings from CO2, CH4, N2O
Post by: Rod on September 03, 2018, 04:02:06 AM

Edit, for your information I have a  BS, MEng & PhD all from UC Berkeley.

PhD from Berkeley in engineering!  I knew you were smart!

Keep posting!   We need more people like you on these forums! 

I'm not smart enough to debate over the RF factors. I know that for a fact.  That is why I like to see you guys carry on the discussion because I can learn from you. 

Thank you for all of your great posts on this forum!
Title: Re: Comparison: forcings from CO2, CH4, N2O
Post by: AbruptSLR on September 04, 2018, 03:13:35 AM
For better or worse, Bloomberg projects a surge in LNG demand for years to come, so it will be hard to control associated anthropogenic methane leaks:

Title: "Global LNG Outlook 2018"

https://about.bnef.com/lng-outlook/

Extract: "“Global imports of LNG will set a new record this year on the back of 7.2% growth. A further surge in demand to 2030 will be driven by environmental measures in China, rising power generation in South and Southeast Asia, and a reduction in domestic gas production in Europe.”"
Title: Re: Comparison: forcings from CO2, CH4, N2O
Post by: AbruptSLR on September 04, 2018, 07:46:56 PM
Here are some of Joe Romm's thoughts on the GWP of methane:

Title: "How The EPA And New York Times Are Getting Methane All Wrong"

https://thinkprogress.org/how-the-epa-and-new-york-times-are-getting-methane-all-wrong-eba3397ce9e5/

Extract: "And although the 100-year GWP is by far the most widely used, the IPCC itself drops this mini-bombshell in their 2013 report:

There is no scientific argument for selecting 100 years compared with other choices (Fuglestvedt et al., 2003; Shine, 2009). The choice of time horizon is a value judgement since it depends on the relative weight assigned to effects at different times.

As of July, EPA’s own web page “Understanding Global Warming Potentials,” stated, “Methane (CH4) is estimated to have a GWP of 28–36 over 100 years.”"
Title: Re: Comparison: forcings from CO2, CH4, N2O
Post by: AbruptSLR on September 07, 2018, 09:55:38 AM
To find out about the potential influence of the loss of atmospheric hydroxyl ions on the GWP of methane (particularly due to the associated increases of ozone, water vapor and carbon dioxide) then you should download, and read, the following linked reference by Isaksen et al (2011), with an open access pdf:

Isaksen, I. S. A., Gauss M., Myhre, G., Walter Anthony, K. M.  and Ruppel, C.,  (2011), "Strong atmospheric chemistry feedback to climate warming from Arctic methane emissions", Global Biogeochem. Cycles, 25, GB2002, doi:10.1029/2010GB003845.

http://onlinelibrary.wiley.com/doi/10.1029/2010GB003845/pdf

Abstract: "The magnitude and feedbacks of future methane release from the Arctic region are unknown. Despite limited documentation of potential future releases associated with thawing permafrost and degassing methane hydrates, the large potential for future methane releases calls for improved understanding of the interaction of a changing climate with processes in the Arctic and chemical feedbacks in the atmosphere. Here we apply a “state of the art” atmospheric chemistry transport model to show that large emissions of CH4 would likely have an unexpectedly large impact on the chemical composition of the atmosphere and on radiative forcing (RF). The indirect contribution to RF of additional methane emission is particularly important. It is shown that if global methane emissions were to increase by factors of 2.5 and 5.2 above current emissions, the indirect contributions to RF would be about 250% and 400%, respectively, of the RF that can be attributed to directly emitted methane alone. Assuming several hypothetical scenarios of CH4 release associated with permafrost thaw, shallow marine hydrate degassing, and submarine landslides, we find a strong positive feedback on RF through atmospheric chemistry. In particular, the impact of CH4 is enhanced through increase of its lifetime, and of atmospheric abundances of ozone, stratospheric water vapor, and CO2 as a result of atmospheric chemical processes. Despite uncertainties in emission scenarios, our results provide a better understanding of the feedbacks in the atmospheric chemistry that would amplify climate warming."

Extract: "CH4 oxidation leads to enhanced formation of ozone in the troposphere and lower stratosphere through a sequence of reactions involving NOx compounds."
Title: Re: Comparison: forcings from CO2, CH4, N2O
Post by: AbruptSLR on September 08, 2018, 04:55:19 PM
It is likely that both the RCP, and the SSP, radiative forcing scenarios underestimate future methane emissions from shallow agricultural reservoirs:

Thomas A. Davidson et al, Synergy between nutrients and warming enhances methane ebullition from experimental lakes, Nature Climate Change (2018). DOI: 10.1038/s41558-017-0063-z


http://www.nature.com/articles/s41558-017-0063-z

Abstract: "Lakes and ponds are important natural sources of the potent greenhouse gas methane (CH4), with small shallow waters identified as particular hotspots. Ebullition (bubbles) of CH4 makes up a large proportion of total CH4 flux. However, difficulty measuring such episodic events5 makes prediction of how ebullition responds to nutrient enrichment and rising temperatures challenging. Here, the world’s longest running, mesocosm-based, shallow lake climate change experiment was used to investigate how the combination of warming and eutrophication (that is, nutrient enrichment) affects CH4 ebullition. Eutrophication without heating increased the relative contribution of ebullition from 51% to 75%. More strikingly the combination of nutrient enrichment and experimental warming treatments of +2–3 °C and +4–5 °C had a synergistic effect, increasing mean annual ebullition by at least 1900 mg CH4-C m−2 yr−1. In contrast, diffusive flux showed no response to eutrophication and only a small increase at higher temperatures (average 63 mg CH4–C m−2 yr−1). As shallow lakes are the most common lake type globally, abundant in highly climate sensitive regions and most vulnerable to eutrophication, these results suggest their current and future contributions to atmospheric CH4 concentrations may be significantly underestimated."

See also, Title: "Combined nutrients and warming massively increase methane emissions from lakes"

https://phys.org/news/2018-01-combined-nutrients-massively-methane-emissions.html

Extract: "Shallow lakes in agricultural landscapes will emit significantly greater amounts of methane, mostly in the form of bubbles (ebullition) in a warmer world, which is a potential positive feedback mechanism to climate warming.

The results here were striking as they showed that the combination of increased nutrient loading and warming had a synergistic effect on the ebullition of methane. In the absence of nutrient enrichment, warming alone increased annual methane ebullition by around 50 percent and its relative contribution to total methane emission rose from about 50 percent to 75 percent.

In stark contrast, when nutrient levels were high, warming increased total methane emission by at least six-fold, and in some cases, 17-fold, and the proportion of ebullition increased to 95 percent of total annual methane flux."
Title: Re: Comparison: forcings from CO2, CH4, N2O
Post by: AbruptSLR on September 08, 2018, 07:27:38 PM
As a follow-on to my last post about underestimates likely future emissions from freshwater reservoirs (especially agricultural reservoirs), the linked article cites an article about a new scientific study that estimates that the U.S. EPA is currently underestimating about 60% of anthropogenic fossil fuel related methane emissions.  This difference gains importance when considering that radiative forcing from methane calculated on an emissions basis is about twice that as on an atmospheric concentration basis:

Title: "US emissions of methane – a potent greenhouse gas – are 60% higher than EPA thinks"

https://www.usatoday.com/story/news/nation/2018/06/21/emissions-greenhouse-gas-methane-higher-than-epa-thinks/722391002/

Extract: "The U.S. oil and gas industry emits 13 million metric tons of methane from its operations each year – nearly 60 percent more than currently estimated by the Environmental Protection Agency, a new study in the journal Science finds."

See also:

http://science.sciencemag.org/content/early/2018/06/20/science.aar7204.full

Title: Re: Comparison: forcings from CO2, CH4, N2O
Post by: AbruptSLR on September 11, 2018, 07:30:03 PM
Fossil fuel emissions of methane will likely increase after the Trump Administration weaken the requirements to monitor for, and to repair methane leaks, which would increased radiative forcing from such methane emissions:

Title: "Trump Administration Wants to Make It Easier to Release Methane Into Air"

https://www.nytimes.com/2018/09/10/climate/methane-emissions-epa.html?rref=collection%2Fissuecollection%2Ftodays-new-york-times

Extract: "The Trump administration, taking its third major step this year to roll back federal efforts to fight climate change, is preparing to make it significantly easier for energy companies to release methane into the atmosphere.

Methane, which is among the most powerful greenhouse gases, routinely leaks from oil and gas wells, and energy companies have long said that the rules requiring them to test for emissions were costly and burdensome.

The Environmental Protection Agency, perhaps as soon as this week, plans to make public a proposal to weaken an Obama-era requirement that companies monitor and repair methane leaks, according to documents reviewed by The New York Times. In a related move, the Interior Department is also expected in coming days to release its final version of a draft rule, proposed in February, that essentially repeals a restriction on the intentional venting and “flaring,” or burning, of methane from drilling operations."
Title: Re: Comparison: forcings from CO2, CH4, N2O
Post by: AbruptSLR on September 11, 2018, 11:35:22 PM
More bad news about both methane, and nitrous oxide, emissions from rice paddies (which means higher than expected radiative forcing from these sources):

Title: "Greenhouse gases from rice paddies may be 2x higher than thought"

https://phys.org/news/2018-09-nitrous-oxide-emissions-rice-farms.html#nRlv

Extract: "The way some irrigated rice paddies are managed worldwide, with cycles of flooding followed by dry periods, may lead to twice the planet-warming greenhouse gas pollution as previously thought, researchers said Monday.

Overall, they calculated that nitrous oxide per hectare (2.5 acres) was three times higher than ever reported by research on intermittently flooded farms before.

"When this new information is extrapolated across the world and embedded into estimates of methane emissions, the net climate impact from both methane and nitrous oxide could be two times higher than previous estimates," Kritee said."
Title: Re: Comparison: forcings from CO2, CH4, N2O
Post by: TeaPotty on September 15, 2018, 04:35:22 AM
Thank you once again AbruptSLR, for finding that link from Joe Romm who closes the argument about Methane's warming potency.

Oh, but where are all the wonderfully "skeptical" conservatives? Where is Ned W,  his defenders, and those who claimed he taught them something new?

Its like you never learn. AbruptSLR makes the same simple argument that Joe Romm made in the 2015 article, presented the same data. Now go look at the last few pages of ridiculous and irrational arguments defending the conservative viewpoint. So detached from reality. Simply utter nonsense.

And somehow, so many discussions follow this path. Its so tiresome, and you conservatives never change. As usual, there is never any reason to apologize or even take fault for being wrong when your bias is conservative. And one conservative usually brings another to post like a choir of nonsense.
Title: Re: Comparison: forcings from CO2, CH4, N2O
Post by: oren on September 15, 2018, 12:48:22 PM
TeaPotty, while ASLR's post is informative, yours is not. I'm not sure whom you are attacking but it's the wrong tone for this forum IMHO.
Title: Re: Comparison: forcings from CO2, CH4, N2O
Post by: gerontocrat on September 15, 2018, 01:30:52 PM
Thank you once again AbruptSLR, for finding that link from Joe Romm who closes the argument about Methane's warming potency.

Oh, but where are all the wonderfully "skeptical" conservatives? Where is Ned W,  his defenders, and those who claimed he taught them something new?

Its like you never learn. AbruptSLR makes the same simple argument that Joe Romm made in the 2015 article, presented the same data. Now go look at the last few pages of ridiculous and irrational arguments defending the conservative viewpoint. So detached from reality. Simply utter nonsense.

And somehow, so many discussions follow this path. Its so tiresome, and you conservatives never change. As usual, there is never any reason to apologize or even take fault for being wrong when your bias is conservative. And one conservative usually brings another to post like a choir of nonsense.
Ned W said nothing about future emissions. The data he used is from NOAA on current and previous greenhouse gases in the atmosphere. NOAA gets the data from its various testing stations around the world. I guess this data is plugged into the models used for the IPCC reports

If the amount of methane, nitrous oxides, whatever are so much higher than reported, how come that is not showing up in the NOAA data? (I am unwilling to accept conspiracy theories - Trumpistan hasn't had time to screw that up yet, and the record to date is in the public domain).

I thought about  Arctic methane - very few measuring stations in the arctic, but these gases only take a few months for world-wide mixing. So I have been unable to find anything that contradicts the NOAA data.

Will these non-CO2 gases increase in the future? My guess is yes.
Will the models used for the IPCC reports under-estimate these emissions?  My guess is yes.
But Ned W was not talking about the future. He was talking about now.

So unless you have some data (totally lacking in your post) to show NOAA's data is wrong, Ned W is right about the situation as at now. Evidence, please, on measurements taken of greenhouse gases in the atmosphere, now and previous years.
Title: Re: Comparison: forcings from CO2, CH4, N2O
Post by: AbruptSLR on September 15, 2018, 04:13:03 PM
So unless you have some data (totally lacking in your post) to show NOAA's data is wrong, Ned W is right about the situation as at now. Evidence, please, on measurements taken of greenhouse gases in the atmosphere, now and previous years.

AR5 explicitly states that policy decisions on CO2, CH4 and N20 should be based on an emissions basis rather than on an atmospheric concentration basis.  As scientists do not need to come to this thread for guidance on how to run their climate models using atmospheric gas concentrations, I suggest than anyone reading this thread does so in order to better understand how to better address climate change; which per AR5 means considering radiative forcing on and emissions basis.  I for one have clearly demonstrated that methane emissions generate ozone, water vapor and carbon dioxide which clearly increase the GWP* of methane well above GWP.

While it is true that on an atmospheric concentration basis that CO2 presently generates much greater radiative forcing than does methane; on an emissions basis over the coming two decades methane generates comparable radiative forcing to that of carbon dioxide.

Edit 1, if this thread is only about radiative forcing from atmospheric concentration, then the title should be changed, otherwise Figure 8-32 from AR5 presenting GWP for 2008 emissions for both 10-year and 20-year periods is relevant to my last point.

Edit 2, if it is note clear to some readers, advanced Earth Systems Models include math that account for the chemical reactions of methane in the atmosphere that generate ozone, stratospheric water vapor and carbon dioxide; which generate radiative forcings that NOAA does not attribute to methane because NOAA reports radiative forcing on an atmospheric concentration basis; while report on an emissions basis would attribute these radiative forcing contributions to the emitted methane that generated them.
Title: Re: Comparison: forcings from CO2, CH4, N2O
Post by: AbruptSLR on September 29, 2018, 01:53:06 AM
As more hurricanes/typhoons/cyclones create more opportunities for termite infestations, we may well see associated methane emission increase above that assumed by AR5:

Title: "Devastating termite infestations threaten more damage in the wake of post-hurricane floods"

https://www.popsci.com/flood-waters-hurricanes-termites?src=SOC&dom=tw

&

Title: "Methane Sources – Termites"

http://www.ghgonline.org/methanetermite.htm

Extract: "Each termite produces, on average, about half a microgram of methane per day, a seemingly insignificant amount. However, when this is multiplied up by the world population of termites, global methane emission from this source is estimated to be about 20 million tonnes each year.

There are more than 2000 different species of termites and the amounts of methane produced varies considerably between species, with some producing no methane at all. Methane is produced in termite guts, by symbiotic bacteria and protozoa, during food digestion.

Termite methane does not always end up going straight into the atmosphere, many species are subterranean or live in above ground earth mounds where much of the methane can be used up by soil methanotrophs before it gets out into the atmosphere."
Title: Re: Comparison: forcings from CO2, CH4, N2O
Post by: Sleepy on September 29, 2018, 06:44:15 AM
TeaPotty, while ASLR's post is informative, yours is not. I'm not sure whom you are attacking but it's the wrong tone for this forum IMHO.
Hmm, I thought this thread was dead when I made my first comment but here's my first thought when it was started: The how is the what. How a thing arises tells you all about what that thing is.

In essence, NedW's very first sentence gave Teapotty and ASLR a green card to post whatever they like in this thread.
Title: Re: Comparison: forcings from CO2, CH4, N2O
Post by: Ned W on October 04, 2018, 02:54:20 PM
In essence, NedW's very first sentence gave Teapotty and ASLR a green card to post whatever they like in this thread.

What a weird comment.  This thread was started in order to look at quantitative comparisons of the radiative forcing from CO2, CH4, and N2O.  One reason for doing that is because I had the impression that many people here don't have a clear mental picture of the relative magnitudes of the forcings from those three agents. 

I'm not in a position to give (or deny) anyone a "green card to post whatever they like".  People who want to keep threads on-topic will limit themselves to posting things that are on-topic; people who don't want to will post whatever they feel like posting.

I stopped posting because (a) I got busy, and (b) the direct, quantitative comparison called for in the thread title had been addressed nicely here (https://forum.arctic-sea-ice.net/index.php/topic,2383.msg168719.html#msg168719):

(https://i.imgur.com/lFdIZSi.png)

and here (https://forum.arctic-sea-ice.net/index.php/topic,2383.msg170691.html#msg170691):

(for the recent past)
(https://i.imgur.com/FVk2IZZ.png)

(and for the next couple of decades)
(https://i.imgur.com/mU1QRJ9.png)

Take-home points that relate to the topic of the thread:

1. The radiative forcing from CO2 in recent decades (say, the past 50 years) has represented by far the largest fraction of the total forcing over that time period. 

2. Since the launch of CMIP5, radiative forcing from CO2 has been slightly below what was projected in RCP8.5, and slightly above what was projected in the other RCPs.  Forcing from CH4 has been quite a bit smaller, both in absolute magnitude and relative to what was projected in RCP8.5, but well higher than the other RCPs.  However, this is a short time period.

3. Over the next three decades, the CMIP5 concentration pathways show that CO2 will continue to be the most important climate forcing, with methane at about one-fifth of the CO2 forcing (in RCP8.5, and much less in the other scenarios).  N2O forcing was projected to be smaller.

All of those forcing values were recalculated using the most up-to-date formulations from Etminan et al. (2016).

We probably could have short-circuited a lot of this, by jumping straight to the IPCC AR5's Figure 8.6(d):

(https://i.imgur.com/g10prph.jpg)

which shows the decadally-averaged annual forcing (W m-2 yr-1) for each of the three gases, but (a) I like to calculate things for myself, and (b) the data in the AR5 figure aren't updated with Etminan's forcings, and I wanted to do that.

So that's the main reason I stopped posting in this thread: the questions implied in the thread topic had been pretty thoroughly answered, as far as I was concerned.
Title: Re: Comparison: forcings from CO2, CH4, N2O
Post by: Sleepy on October 05, 2018, 07:56:48 AM
This thread was started in order to look at quantitative comparisons of the radiative forcing from CO2, CH4, and N2O.
That is exactly what I think you should have done and left your impressions out of it. You never get an impression of those who don't participate.
Title: Re: Comparison: forcings from CO2, CH4, N2O
Post by: AbruptSLR on October 05, 2018, 02:35:07 PM
This thread was started in order to look at quantitative comparisons of the radiative forcing from CO2, CH4, and N2O.
That is exactly what I think you should have done and left your impressions out of it. You never get an impression of those who don't participate.

AR5 explicitly states that policy decisions on CO2, CH4 and N20 should be based on an emissions basis rather than on an atmospheric concentration basis.
Title: Re: Comparison: forcings from CO2, CH4, N2O
Post by: Ned W on October 07, 2018, 01:43:06 AM
We have already had this argument, and it annoyed the rest of ASIF no end.  So I won't repeat myself, and won't be drawn in to another endless back-and-forth. 

This (http://forum.arctic-sea-ice.net/index.php/topic,2383.msg169564.html#msg169564) was my response the first time you made that claim, so anyone who cares can re-read it.  AR5 is absolutely 100% clear that both concentration-based and emissions-based forcings are valid metrics for their own purposes.  In general AR5 uses concentration-based forcings for science and emissions-based forcings for policy.

This topic area on ASIF is labeled Science.  If you do not want to see concentration-based forcings -- which are almost universal in discussions among climate scientists -- you should start your own thread in the Policy section of ASIF.

I am still pretty pissed off about what happened in the first four pages of this thread and am not in the mood to repeat the experience. So, seriously, I would request that you start your own thread over in the Policy area and post to your heart's content there.

Thanks.
Title: Re: Comparison: forcings from CO2, CH4, N2O
Post by: AbruptSLR on October 07, 2018, 02:39:29 PM
One should never let self-righteous indignation get in the way of a healthy scientific discussion, thus I note the following two issues that many bloggers may be overlooking about radiative forcing associate with methane emissions:

1. When anthropogenic methane is emitted into the atmosphere it initiates a chain reaction of chemical interactions that not only consumes hydroxyl ions but also generate ozone, stratospheric water vapor and carbon dioxide, all of which generate radiative forcing that would not have occurred if the methane had never been emitted.

2. Reductions in the atmospheric hydroxyl ions (which can occur due to a large short-term pulse of methane emissions) slows down the rate of the chemical chain reactions cited in my first point; which then extends the average residency life of methane in the atmosphere, which results in more radiative forcing.

Furthermore, the attached image is Figure 2 from Shindell et al (2009) indicates 100-year GWP values for methane of 25 without aerosol effects, and 34 with both direct and indirect aerosol effects.  Also, if you read the caption for this figure you will see that the 20-year GWP value for methane is 79 without aerosol effects and is 105 with both direct and indirect aerosol effects (see linked pdf also)

Shindell, D.T., Faluvegi, G., Koch, D.M., Schmidt, G.A., Unger, N., and Bauer S.E. (2009), "Improved Attribution of Climate Forcing to Emissions" Science, Vol. 326 no. 5953 pp. 716-718, DOI: 10.1126/science.1174760.

http://saive.com/911/DOCS/AAAS-Aerosols-not-CO2-Cause-Global-Warming.pdf

However, the AR5 (2013) only cites a 20-year GWP for methane of 86 (see below):

Methane GWP value and lifetime from 2013 IPCC AR5 p714
Lifetime: 12.4 years
GWP over 20 years: 86
GWP over 100 years: 34

And if one is truly concerned about the potential influence of the loss of atmospheric hydroxyl ions on the GWP of methane, one can download, and read, the following linked reference by Isaksen et al (2011), with an open access pdf:

Isaksen, I. S. A., Gauss M., Myhre, G., Walter Anthony, K. M.  and Ruppel, C.,  (2011), "Strong atmospheric chemistry feedback to climate warming from Arctic methane emissions", Global Biogeochem. Cycles, 25, GB2002, doi:10.1029/2010GB003845.

http://onlinelibrary.wiley.com/doi/10.1029/2010GB003845/pdf
Also I note that the linked reference (with an open access pdf) emphasizes our current poor understanding of the current and future atmospheric compositions with regard to ozone and hydroxyl ions as emphasized by the following extract showing that the hydroxyl driven lifetime for methane predicted by different models differ by a factor of 2 (which is not very reassuring).

Extract: "The oxidation capacity of the atmosphere remains poorly characterised in a number of environmentally sensitive regions, with an order of magnitude difference between measurements and models. Both measurements and our understanding of the key chemical processes have large uncertainties. One example of this lack of understanding is the uncertainty in future methane concentrations, with models predicting •OH driven lifetimes that differ by a factor of 2."

S. Madronich,   M. Shao,   S. R. Wilson,   K. R. Solomon,   J. D. Longstreth and   X. Y. Tang, (2015), "Changes in air quality and tropospheric composition due to depletion of stratospheric ozone and interactions with changing climate: implications for human and environmental health",  Photochem. Photobiol. Sci.,14, 149-169, DOI: 10.1039/C4PP90037E


http://pubs.rsc.org/en/content/articlelanding/2015/pp/c4pp90037e#!divAbstract

Abstract: "UV radiation is an essential driver for the formation of photochemical smog, which includes ground-level ozone and particulate matter (PM). Recent analyses support earlier work showing that poor outdoor air quality is a major environmental hazard as well as quantifying health effects on regional and global scales more accurately. Greater exposure to these pollutants has been linked to increased risks of cardiovascular and respiratory diseases in humans and is associated globally with several million premature deaths per year. Ozone also has adverse effects on yields of crops, leading to loss of billions of US dollars each year. These detrimental effects also may alter biological diversity and affect the function of natural ecosystems. Future air quality will depend mostly on changes in emission of pollutants and their precursors, but changes in UV radiation and climate will contribute as well. Significant reductions in emissions, mainly from the energy and transportation sectors, have already led to improved air quality in many locations. Air quality will continue to improve in those cities/states that can afford controls, and worsen where the regulatory infrastructure is not available. Future changes in UV radiation and climate will alter the rates of formation of ground-level ozone and photochemically-generated particulate matter and must be considered in predictions of air quality. The decrease in UV radiation associated with recovery of stratospheric ozone will, according to recent global atmospheric model simulations, lead to increases in ground-level ozone at most locations. If correct, this will add significantly to future ground-level ozone trends. However, the spatial resolution of these global models is insufficient to inform policy at this time, especially for urban areas. UV radiation affects the atmospheric concentration of hydroxyl radicals, ˙OH, which are responsible for the self-cleaning of the atmosphere. Recent measurements confirm that, on a local scale, ˙OH radicals respond rapidly to changes in UV radiation. However, on large (global) scales, models differ in their predictions by nearly a factor of two, with consequent uncertainties for estimating the atmospheric lifetime and concentrations of key greenhouse gases and air pollutants. Projections of future climate need to consider these uncertainties. No new negative environmental effects of substitutes for ozone depleting substances or their breakdown-products have been identified. However, some substitutes for the ozone depleting substances will continue to contribute to global climate change if concentrations rise above current levels."

Also, see:
Matthew Rigby et al. (2017), "Role of atmospheric oxidation in recent methane growth", PNAS, Vol. 114, No. 21, pp 5373-5377.

http://www.pnas.org/content/pnas/114/21/5373.full.pdf

Extract: "We find a 64–70% probability that a decline in OH has contributed to the post-2007 methane rise.

Here, we show that changes in the major methane sink, the hydroxyl radical, have likely played a substantial role in the global methane growth rate. This work has significant implications for our understanding of the methane budget, which is important if we are to better predict future changes in this potent greenhouse gas and effectively mitigate enhanced radiative forcing caused by anthropogenic emissions. "
Title: Re: Comparison: forcings from CO2, CH4, N2O
Post by: Ned W on October 07, 2018, 04:54:15 PM
Quote
1. When anthropogenic methane is emitted into the atmosphere it ... generate ozone, stratospheric water vapor and carbon dioxide, all of which generate radiative forcing that would not have occurred if the methane had never been emitted.

That's true.  But let's quantify it,  please, so people reading this understand how important (or not) the effect is.

Over, say, the past two decades, do you think the radiative forcing from the methane-derived fractions of those three factors adds up to ... 1% of the forcing from CO2 during the same time period?  2%?  More?  Less?

When doing that calculation, remember that methane is measured in ppb while CO2 is in ppm.

Quote
... GWP ...

GWP is computationally irrelevant to the radiative forcing values shown here.  You could use a 50 year GWP of 1 or 100 for methane, and it would not change any of the graphs I've posted.
Title: Re: Comparison: forcings from CO2, CH4, N2O
Post by: AbruptSLR on October 07, 2018, 06:07:50 PM
Attached is Figure 8-17 from AR5, which shows that when the stratospheric water vapor component and ozone component and the associated methane component are added together their combined radiative forcing is comparable to that of carbon dioxide

See:

https://www.ipcc.ch/report/graphics/index.php?t=Assessment%20Reports&r=AR5%20-%20WG1&f=Chapter%2008
or
http://www.climatechange2013.org/report/reports-graphic/ch8-graphics/
Title: Re: Comparison: forcings from CO2, CH4, N2O
Post by: Ned W on October 07, 2018, 09:58:23 PM
That's from 1750 to now.  As I've explained in this thread, most of the CH4 forcing was in the past (especially mid-20th century).  In recent decades, the methane forcing has been extremely small.  Here's figure 8.6(d) from AR5 again:

(https://i.imgur.com/g10prph.jpg)

Note the relative size of the green bar, which is the methane forcing.  The CH4-to-ozone, CH4-to-strat-H2O, and CH4-to-CO2 forcings would be significantly smaller than the green bar itself.
Title: Re: Comparison: forcings from CO2, CH4, N2O
Post by: AbruptSLR on October 07, 2018, 10:36:27 PM
As stated previously per Rigby et al (2017) there is a 64 to 70% probability that a decline in hydroxyl ions in the atmosphere has contributed to the post-2007 increase in atmospheric methane concentration.  If so this means that the residency life of methane in the atmosphere is higher than assumed by AR5:

Matthew Rigby et al. (2017), "Role of atmospheric oxidation in recent methane growth", PNAS, Vol. 114, No. 21, pp 5373-5377.

http://www.pnas.org/content/pnas/114/21/5373.full.pdf

Extract: "We find a 64–70% probability that a decline in OH has contributed to the post-2007 methane rise."
Title: Re: Comparison: forcings from CO2, CH4, N2O
Post by: oren on October 08, 2018, 12:03:04 AM
Quote
In recent decades, the methane forcing has been extremely small. 
Indeed. But not because nothing happened with methane. Rather methane emissions were almost cancelled out with atmospheric methane decay. But had there been no methane emissions, we would have had a significant negative methane forcing. Ignoring this dynamic while posting comments that methane is not important due to its stable concentration (and relegating emissions to policy), is I think the reason why this thread is eliciting emotional responses.
Humans are increasing CO2 concentrations (visibly affecting RF) and maintaining methane concentrations from dropping (invisibly affecting RF). I think both of these are important.
As the focus of this thread is narrowly defined as the RF with a 1 year moving baseline, would you be willing to calculate and present RF resulting from a reduction of 10% in methane concentration over 1 year while all other GHG concentrations remain stable at current levels? (This would occur naturally should humans decide to shift policy and stop emitting GHGs). This RF information could help readers who desire to discuss the relative merits of various policies in the yet-unopened policy thread.
Title: Re: Comparison: forcings from CO2, CH4, N2O
Post by: Ned W on October 08, 2018, 01:53:04 AM
Thanks for the comment, Oren.  You've brought up this idea before and I'm not sure what to think about it, mainly because I'm not sure what the relative costs and obstacles are for different approaches to reducing the total forcing from greenhouse gases.  But you made a very straightforward request, so let's tackle it. 

We can start with the 2017 NOAA AGGI data on atmospheric concentrations for CO2, CH4, and N2O.  Assume that CH4 is cut by 10% over some period of time (it actually doesn't matter how long) while CO2 and N2O stay the same. 

Using the formulations from Etminan (2016), that 10% drop in CH4 would provide a (negative) radiative forcing of -0.08 W/m2.  How much cooling that would produce depends on what value you choose for climate sensitivity.  Likewise, it would take some time to have its full effect (just as we now speak of "warming in the pipeline", in a hypothetical case of negative forcings we would need to speak of "cooling in the pipeline"....)

Is that a large amount or a small amount?  Depends on how you choose to look at it, I suppose.  For comparison, the normal annual increase in CO2 in recent years has created an annual forcing around +0.03 W/m2.  So dropping the concentration of methane in the atmosphere by 10% would be equivalent to just under three years' worth of the annual increment in CO2 concentration.
Title: Re: Comparison: forcings from CO2, CH4, N2O
Post by: Ned W on October 08, 2018, 02:09:28 AM
As a check on my calculations ... a 10% cut in atmospheric methane concentration would put us back at 1984-era values.  Per NOAA AGGI, the methane forcing in 2017 was 0.509, while in 1984 it was 0.432, giving a negative forcing of -0.077 W/m2, basically the same as my -0.08.
Title: Re: Comparison: forcings from CO2, CH4, N2O
Post by: Ned W on October 10, 2018, 02:09:32 PM
Here's some more context: a comparison of the WMGHGs to all the other major categories of anthropogenic forcing:

(https://i.imgur.com/Plh30lr.jpg)

The darkest bars are the forcing over the past 30 years (1988-2018).  Lighter bars are the two previous 30-year periods (1958 to 1988, and 1928 to 1958) for comparison.

What's kind of stunning is that during the past 30 years, every other bar [positive or negative] is less than 10% of the magnitude of the CO2 forcing.

Other comments

* Methane, N2O, halocarbons, fluorocarbons, and tropospheric ozone were the largest non-CO2 forcings [in that order], but all were pretty small.

* Over this period, there has been no large negative anthropogenic forcing.  Aerosols barely produced any forcing at all over the past 30 years, and if you combine the direct and indirect (cloud albedo) effects, they nearly cancel out entirely.

* Non-anthro forcings (solar and volcanic) probably each produced a small negative forcing over the past 30 years (not shown).

* Oren asked about the impact of a 10% decrease in atmospheric methane.  As shown in the previous post, that would create a negative forcing of -0.08 W/m2, basically dropping the methane bar in this graph to near 0.

* a 10% decrease in aerosols would produce a positive forcing of around +0.11 W/m2 (direct+indirect).

Key:

CO2_RF: CO2 Forcing
CH4_RF: Methane Forcing
N2O_RF: Nitrous Oxide Forcing
FGASSUM_RF: Total forcing from all fluorinated gases controlled under the Kyoto Protocol (HFCs, PFCs, SF6)
MHALOSUM_RF: Total forcing from all gases controlled under the Montreal Protocol
TOTAER_DIR_RF: Total direct aerosol forcing
CLOUD_TOT_RF: Cloud albedo effect
STRATOZ_RF: Stratospheric ozone forcing
TROPOZ_RF: Tropospheric ozone forcing
CH4OXSTRATH2O_RF: Stratospheric water-vapour from methane oxidization
LANDUSE_RF: Land-use albedo
BCSNOW_RF: Black carbon on snow

Source:

http://www.pik-potsdam.de/~mmalte/rcps/
http://www.pik-potsdam.de/~mmalte/rcps/data/RCP85_MIDYEAR_RADFORCING.xls
Title: Re: Comparison: forcings from CO2, CH4, N2O
Post by: TerryM on October 10, 2018, 05:54:24 PM
Ned
Per your chart the Montreal protocol seems to have been a huge success.
Is there anything on the table that could yield rapid results of like magnitude?
Thanks
Terry
Title: Re: Comparison: forcings from CO2, CH4, N2O
Post by: Ned W on October 10, 2018, 06:43:31 PM
It sure reversed what had been a terrifying trend.  You normally see that shown in terms of ozone depletion, but it's interesting to see it also represented in the direct climate forcing from halocarbon gases.
Title: Re: Comparison: forcings from CO2, CH4, N2O
Post by: AbruptSLR on October 10, 2018, 07:19:28 PM
With some countries cheating on the Montreal Protocol agreement, who knows how future hydrofluorocarbon and chlorofluorocarbons will have on atmospheric hydroxyl ion and ozone concentrations (with associated impacts of radiative forcing):

Montzka, S.A., G.S. Dutton, P. Yu, E. Ray, R. Portmann, J.S. Daniel, L. Kuijpers, B.D. Hall, D. Mondeel, C. Siso, D. Nance, M. Rigby, A. Manning, L. Hu, F. Moore, B.R. Miller, and J.W. Elkins, An unexpected and persistent increase in global emissions of ozone-depleting CFC-11, Nature, doi:10.1038/s41586-018-0106-2, 2018.

http://www.nature.com/articles/s41586-018-0106-2

Abstract:
The Montreal Protocol was designed to protect the stratospheric ozone layer by enabling reductions in the abundance of ozone-depleting substances such as chlorofluorocarbons (CFCs) in the atmosphere1,2,3. The reduction in the atmospheric concentration of trichlorofluoromethane (CFC-11) has made the second-largest contribution to the decline in the total atmospheric concentration of ozone-depleting chlorine since the 1990s1. However, CFC-11 still contributes one-quarter of all chlorine reaching the stratosphere, and a timely recovery of the stratospheric ozone layer depends on a sustained decline in CFC-11 concentrations1. Here we show that the rate of decline of atmospheric CFC-11 concentrations observed at remote measurement sites was constant from 2002 to 2012, and then slowed by about 50 per cent after 2012. The observed slowdown in the decline of CFC-11 concentration was concurrent with a 50 per cent increase in the mean concentration difference observed between the Northern and Southern Hemispheres, and also with the emergence of strong correlations at the Mauna Loa Observatory between concentrations of CFC-11 and other chemicals associated with anthropogenic emissions. A simple model analysis of our findings suggests an increase in CFC-11 emissions of 13 ± 5 gigagrams per year (25 ± 13 per cent) since 2012, despite reported production being close to zero4 since 2006. Our three-dimensional model simulations confirm the increase in CFC-11 emissions, but indicate that this increase may have been as much as 50 per cent smaller as a result of changes in stratospheric processes or dynamics. The increase in emission of CFC-11 appears unrelated to past production; this suggests unreported new production, which is inconsistent with the Montreal Protocol agreement to phase out global CFC production by 2010.

Also see:

Title: "Observational evidence for interhemispheric hydroxyl parity"

https://m.phys.org/news/2014-09-evidence-interhemispheric-hydroxyl-parity.html

Extract: "Although state-of-the-art chemistry-transport models predict that the OH concentration in the NH is ~28% (13–42%) higher than in the SH, the present detailed study derives a NH/SH OH ratio of 0.97±0.12 (Figure 3). Uncertainties about the relative abundance of OH in the two hemispheres have persisted since the early 1990s due to uncertainties about how much CH3CCl3 was actually released into the atmosphere and also due to imperfections in interhemispheric transport in models used to estimate OH concentrations."

&

P. K. Patra, M. C. Krol, S. A. Montzka, T. Arnold, E. L. Atlas, + et al. (2014), "Observational evidence for interhemispheric hydroxyl-radical parity", Nature 513, 219-223 DOI: 10.1038/nature13721

http://www.nature.com/articles/nature13721
Title: Re: Comparison: forcings from CO2, CH4, N2O
Post by: TerryM on October 10, 2018, 08:17:55 PM
Not sure if it's still in place, but the US at one time insisted on exempting it's military from compliance with the Montreal Protocol.


Terry
Title: Re: Comparison: forcings from CO2, CH4, N2O
Post by: oren on October 15, 2018, 03:51:54 AM
We can start with the 2017 NOAA AGGI data on atmospheric concentrations for CO2, CH4, and N2O.  Assume that CH4 is cut by 10% over some period of time (it actually doesn't matter how long) while CO2 and N2O stay the same. 

Using the formulations from Etminan (2016), that 10% drop in CH4 would provide a (negative) radiative forcing of -0.08 W/m2.

Is that a large amount or a small amount?  Depends on how you choose to look at it, I suppose.  For comparison, the normal annual increase in CO2 in recent years has created an annual forcing around +0.03 W/m2.  So dropping the concentration of methane in the atmosphere by 10% would be equivalent to just under three years' worth of the annual increment in CO2 concentration.
Thank you Ned for this calculation, and apologies for my delay in responding.
My layman's choice of how to look at this result:
10% would be the annual reduction of methane concentration should methane emissions stop. Therefore, annual methane emissions are equal to a 0.08 W/m2 forcing: 0 W/m2 compared to "natural baseline" of -0.08 W/m2. (I am ignoring non-anthropogenic and feedback methane emissions, so this is an overstatement).
What would be the annual reduction in CO2 concentration should CO2 emissions stop? I read somewhere that 50% of emitted anthropogenic CO2 is absorbed each year. If true, CO2 concentration would drop annually by the magnitude it currently rises each year, and result in an annual forcing of negative 0.03 W/m2, instead of the current positive forcing of similar magnitude. (Or CO2 would drop by much less than it currently rises, leading to a negative forcing <<0.03 W/m2. I am not sure which is correct)
Therefore, annual CO2 emissions are equal to a 0.06 W/m2 forcing: +0.03 W/m2 compared to "natural baseline" of -0.03 W/m2.
So the bottom line of this very crude "analysis" is that methane emissions cause roughly the same annual forcing as CO2 emissions, and are certainly not negligible, although at face value methane concentration is unchanging and therefore contributes almost nothing to changes in forcing. Note this result is independent of costs and obstacles and all the policy issues of reducing anthropogenic emissions.
(Of course, after a few years the methane effect would diminish as its concentration dropped).
I could be quite wrong in my rough numbers (I am sure you can improve this quite a bit), but I think this is the proper way of looking at the RF data and using it to assess emissions data. From  this point onward it's policy discussions of how to tackle emissions and what is more cost-effective to do, but until this point IMHO it's pure science and belongs in this thread. When discussing concentration changes and the resultant RF as a basis for informing policy we cannot ignore the effects of emissions and natural sinks. We must consider a baseline of no anthropogenic emissions, calculating a natural baseline RF to which all should be compared.
Title: Re: Comparison: forcings from CO2, CH4, N2O
Post by: Ned W on October 17, 2018, 02:22:22 PM
Thanks for sharing your thoughts, Oren.  I think I understand where you're coming from and what you're trying to show.  But I think that if you look closely at it, you'll see that your approach doesn't actually work.  Bear with me here:

You are trying to calculate an annual radiative forcing that would represent the impact of a single year's anthropogenic emissions.  In essence, you're trying to back-calculate something like an emissions-based forcing, or GWP, or GTP.  But you're only considering the impact of this year's emissions on climate for one year.  In other words, it's like GSY's insistence on calculating a 1-year GWP for methane.  Yes, it can be done, but it's not a physically meaningful representation of the impact of methane vs CO2 emissions on the climate. 

What you're actually showing is that a given mass of methane has a much stronger radiative forcing than CO2 does over the very short term (1 year).  But we already all know that.  If you instantaneously stopped all anthropogenic emissions of both methane and CO2, the cooling from the loss of methane would be very high in year 1, but would rapidly taper off.  In contrast, the cooling from the loss of CO2 would keep going for centuries, and it would soon eclipse the effect of methane.
Title: Re: Comparison: forcings from CO2, CH4, N2O
Post by: Ned W on October 17, 2018, 02:46:20 PM
FWIW, in working on the previous post I repeatedly wrote, deleted, and re-wrote some additional paragraphs arguing that what you're deriving is not in fact a radiative forcing (W/m2) at all, but should really be considered a "radiant exposure" (J/m2). 

But the explanation was probably too subtle to be worth dealing with here.  The more important issue is just that your comparison of the effects of CO2 and CH4 is ignoring the great difference in their residence time, and thus leading to an unrealistic result.
Title: Re: Comparison: forcings from CO2, CH4, N2O
Post by: AbruptSLR on October 18, 2018, 11:56:07 PM
Stratospheric ozone is under assault from anthropogenic emissions (primarily from East Asia) of several chlorine-containing very short-lived substances (Cl-VSLSs).  This could extend the life of methane in the atmosphere:

Oram, D. E., Ashfold, M. J., Laube, J. C., Gooch, L. J., Humphrey, S., Sturges, W. T., Leedham-Elvidge, E., Forster, G. L., Harris, N. R. P., Mead, M. I., Samah, A. A., Phang, S. M., Ou-Yang, C.-F., Lin, N.-H., Wang, J.-L., Baker, A. K., Brenninkmeijer, C. A. M., and Sherry, D.: A growing threat to the ozone layer from short-lived anthropogenic chlorocarbons, Atmos. Chem. Phys., 17, 11929-11941, https://doi.org/10.5194/acp-17-11929-2017, 2017.

https://www.atmos-chem-phys.net/17/11929/2017/?utm_content=bufferb397a&utm_medium=social&utm_source=twitter.com&utm_campaign=buffer

Abstract. Large and effective reductions in emissions of long-lived ozone-depleting substance (ODS) are being achieved through the Montreal Protocol, the effectiveness of which can be seen in the declining atmospheric abundances of many ODSs. An important remaining uncertainty concerns the role of very short-lived substances (VSLSs) which, owing to their relatively short atmospheric lifetimes (less than 6 months), are not regulated under the Montreal Protocol. Recent studies have found an unexplained increase in the global tropospheric abundance of one VSLS, dichloromethane (CH2Cl2), which has increased by around 60 % over the past decade. Here we report dramatic enhancements of several chlorine-containing VSLSs (Cl-VSLSs), including CH2Cl2 and CH2ClCH2Cl (1,2-dichloroethane), observed in surface and upper-tropospheric air in East and South East Asia. Surface observations were, on occasion, an order of magnitude higher than previously reported in the marine boundary layer, whilst upper-tropospheric data were up to 3 times higher than expected. In addition, we provide further evidence of an atmospheric transport mechanism whereby substantial amounts of industrial pollution from East Asia, including these chlorinated VSLSs, can rapidly, and regularly, be transported to tropical regions of the western Pacific and subsequently uplifted to the tropical upper troposphere. This latter region is a major provider of air entering the stratosphere, and so this mechanism, in conjunction with increasing emissions of Cl-VSLSs from East Asia, could potentially slow the expected recovery of stratospheric ozone.
Title: Re: Comparison: forcings from CO2, CH4, N2O
Post by: AbruptSLR on November 10, 2018, 06:16:33 PM
The linked reference shows the significant impact of methane on climate change, when appropriately considering both the direct and indirect forcing contributions (see the attached image):

Ocko, I. B., Naik, V., and Paynter, D.: Rapid and reliable assessment of methane impacts on climate, Atmos. Chem. Phys., 18, 15555-15568, https://doi.org/10.5194/acp-18-15555-2018, 2018.

https://www.atmos-chem-phys.net/18/15555/2018/

Abstract. It is clear that the most effective way to limit global temperature rise and associated impacts is to reduce human emissions of greenhouse gases, including methane. However, quantification of the climate benefits of mitigation options are complicated by the contrast in the timescales at which short-lived climate pollutants, such as methane, persist in the atmosphere compared to carbon dioxide. Whereas simple metrics fail to capture the differential impacts across all timescales, sophisticated climate models that can address these temporal dynamics are often inaccessible, time-intensive, require special infrastructure, and include high unforced interannual variability that makes it difficult to analyse small changes in forcings. On the other hand, reduced-complexity climate models that use basic knowledge from observations and complex Earth system models offer an ideal compromise in that they provide quick, reliable insights into climate responses, with only limited computational infrastructure needed. They are particularly useful for simulating the response to forcings of small changes in different climate pollutants, due to the absence of internal variability. In this paper, we build on previous evaluations of the freely available and easy-to-run reduced-complexity climate model MAGICC by comparing temperature responses to historical methane emissions to those from a more complex coupled global chemistry–climate model, GFDL-CM3. While we find that the overall forcings and temperature responses are comparable between the two models, the prominent role of unforced variability in CM3 demonstrates how sophisticated models are potentially inappropriate tools for small forcing scenarios. On the other hand, we find that MAGICC can easily and rapidly provide robust data on climate responses to changes in methane emissions with clear signals unfettered by variability. We are therefore able to build confidence in using reduced-complexity climate models such as MAGICC for purposes of understanding the climate implications of methane mitigation.
Title: Re: Comparison: forcings from CO2, CH4, N2O
Post by: AbruptSLR on November 11, 2018, 04:32:17 PM
The linked Columbia website (reflective James Hansen's thinking) on effective radiative forcing, and it calculates the effective radiative forcing of methane to include: "… simulated CH4-induced changes of O3 and stratospheric H2O …".

Title: "Radiative Forcings"

http://www.columbia.edu/~mhs119/Forcings/

Extract: "Fe provides a good prediction of the response to different forcing amounts.

The time dependent effective forcings relative to 1850 for the agents used in our computations are shown individually and as the total in the graph below."

See also:

Hansen et al (2017), "Young people’s burden: requirement of negative CO₂ emissions", Earth Syst. Dynam., 8, 577–616, https://doi.org/10.5194/esd-8-577-2017

https://www.earth-syst-dynam.net/8/577/2017/esd-8-577-2017.pdf

Extract: "The CH4 forcing includes its indirect effects, as increasing atmospheric CH4 causes tropospheric ozone (O3) and stratospheric water vapor to increase (Myhre et al., 2013)."
Title: Re: Comparison: forcings from CO2, CH4, N2O
Post by: Tom_Mazanec on April 20, 2019, 02:01:06 PM
Rising methane levels imperils Paris agreement:

https://eos.org/research-spotlights/rising-methane-emissions-could-derail-the-paris-agreement

EDIT: Here are Feb 2019 stats on CH4:
https://www.esrl.noaa.gov/gmd/ccgg/trends_ch4/

EDIT 2: Industrial emissions of CH4 100 times greater than previously thought:
http://news.cornell.edu/stories/2019/06/industrial-methane-emissions-are-100-times-higher-reported-researchers-say

EDIT 3: Permafrost releasing twelve times as much nitrous oxide as thought:
https://news.harvard.edu/gazette/story/2019/06/harvard-chemist-permafrost-n2o-levels-12-times-higher-than-expected/
Title: Re: Comparison: forcings from CO2, CH4, N2O
Post by: Tom_Mazanec on September 13, 2019, 09:45:33 PM
What Is Nitrous Oxide and Why Is It a Climate Threat?
https://insideclimatenews.org/news/11092019/nitrous-oxide-climate-pollutant-explainer-greenhouse-gas-agriculture-livestock
Quote
For years, experts have warned about the risks from one pollutant in particular—nitrous oxide—and yet there's been little global action on it.

The reason: "It is intimately connected to food," said Ravi Ravishankara, an atmospheric chemist at Colorado State University who co-chaired a United Nations panel on stratospheric ozone from 2007 to 2015.