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AbruptSLR

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Re: Comparison: forcings from CO2, CH4, N2O
« Reply #50 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."
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AbruptSLR

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Re: Comparison: forcings from CO2, CH4, N2O
« Reply #51 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
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Ned W

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Re: Comparison: forcings from CO2, CH4, N2O
« Reply #52 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.

AbruptSLR

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Re: Comparison: forcings from CO2, CH4, N2O
« Reply #53 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.
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TeaPotty

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Re: Comparison: forcings from CO2, CH4, N2O
« Reply #54 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?

GoSouthYoungins

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Re: Comparison: forcings from CO2, CH4, N2O
« Reply #55 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?
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SteveMDFP

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Re: Comparison: forcings from CO2, CH4, N2O
« Reply #56 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

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

AbruptSLR

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Re: Comparison: forcings from CO2, CH4, N2O
« Reply #57 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
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GoSouthYoungins

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Re: Comparison: forcings from CO2, CH4, N2O
« Reply #58 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.



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AbruptSLR

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Re: Comparison: forcings from CO2, CH4, N2O
« Reply #59 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

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"
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AbruptSLR

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Re: Comparison: forcings from CO2, CH4, N2O
« Reply #60 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.
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SteveMDFP

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Re: Comparison: forcings from CO2, CH4, N2O
« Reply #61 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.

Ned W

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Re: Comparison: forcings from CO2, CH4, N2O
« Reply #62 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? 


Ned W

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Re: Comparison: forcings from CO2, CH4, N2O
« Reply #63 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.   

Richard Rathbone

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Re: Comparison: forcings from CO2, CH4, N2O
« Reply #64 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.

jai mitchell

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Re: Comparison: forcings from CO2, CH4, N2O
« Reply #65 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.
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GoSouthYoungins

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Re: Comparison: forcings from CO2, CH4, N2O
« Reply #66 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.
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AbruptSLR

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Re: Comparison: forcings from CO2, CH4, N2O
« Reply #67 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.
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AbruptSLR

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Re: Comparison: forcings from CO2, CH4, N2O
« Reply #68 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).
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GoSouthYoungins

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Re: Comparison: forcings from CO2, CH4, N2O
« Reply #69 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.
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AbruptSLR

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Re: Comparison: forcings from CO2, CH4, N2O
« Reply #70 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.
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AbruptSLR

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Re: Comparison: forcings from CO2, CH4, N2O
« Reply #71 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.
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Re: Comparison: forcings from CO2, CH4, N2O
« Reply #72 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.
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Ned W

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Re: Comparison: forcings from CO2, CH4, N2O
« Reply #73 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:



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
« Last Edit: August 22, 2018, 01:14:57 PM by Ned W »

AbruptSLR

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Re: Comparison: forcings from CO2, CH4, N2O
« Reply #74 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.

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magnamentis

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Re: Comparison: forcings from CO2, CH4, N2O
« Reply #75 on: August 22, 2018, 05:05:20 PM »
one of the most interesting exchanges since long, keep going, a lot to learn here.
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AbruptSLR

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Re: Comparison: forcings from CO2, CH4, N2O
« Reply #76 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
« Last Edit: August 22, 2018, 05:57:29 PM by AbruptSLR »
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GoSouthYoungins

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Re: Comparison: forcings from CO2, CH4, N2O
« Reply #77 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.
big time oops

AbruptSLR

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Re: Comparison: forcings from CO2, CH4, N2O
« Reply #78 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."
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Re: Comparison: forcings from CO2, CH4, N2O
« Reply #79 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...

 :-\

Ned W

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Re: Comparison: forcings from CO2, CH4, N2O
« Reply #80 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.

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Re: Comparison: forcings from CO2, CH4, N2O
« Reply #81 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.
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GoSouthYoungins

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Re: Comparison: forcings from CO2, CH4, N2O
« Reply #82 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?

big time oops

Ned W

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Re: Comparison: forcings from CO2, CH4, N2O
« Reply #83 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.

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Re: Comparison: forcings from CO2, CH4, N2O
« Reply #84 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.
big time oops

Ned W

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Re: Comparison: forcings from CO2, CH4, N2O
« Reply #85 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, I'm not optimistic that you'll stop mangling this stuff like a bull in a mathematical china shop.


AbruptSLR

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Re: Comparison: forcings from CO2, CH4, N2O
« Reply #86 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."
« Last Edit: August 22, 2018, 11:33:43 PM by AbruptSLR »
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Re: Comparison: forcings from CO2, CH4, N2O
« Reply #87 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.
« Last Edit: August 22, 2018, 10:11:36 PM by GoSouthYoungins »
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Re: Comparison: forcings from CO2, CH4, N2O
« Reply #88 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.
« Last Edit: August 23, 2018, 04:58:07 AM by TeaPotty »

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Re: Comparison: forcings from CO2, CH4, N2O
« Reply #89 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.


« Last Edit: August 23, 2018, 07:56:19 AM by Pmt111500 »
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Re: Comparison: forcings from CO2, CH4, N2O
« Reply #90 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
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

How much does it matter if we get the final blow by the CO2T-Rex or the CH4Raptor? Or the one we never saw ...
Omnia mirari, etiam tritissima.
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Re: Comparison: forcings from CO2, CH4, N2O
« Reply #91 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.
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Re: Comparison: forcings from CO2, CH4, N2O
« Reply #92 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.

AbruptSLR

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Re: Comparison: forcings from CO2, CH4, N2O
« Reply #93 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.
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Re: Comparison: forcings from CO2, CH4, N2O
« Reply #94 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.

magnamentis

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Re: Comparison: forcings from CO2, CH4, N2O
« Reply #95 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 ;)
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Re: Comparison: forcings from CO2, CH4, N2O
« Reply #96 on: August 23, 2018, 10:49:45 PM »
Thanks Ned for your detailed response.

AbruptSLR

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Re: Comparison: forcings from CO2, CH4, N2O
« Reply #97 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. ;)
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Rod

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Re: Comparison: forcings from CO2, CH4, N2O
« Reply #98 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. 
« Last Edit: August 24, 2018, 05:56:14 AM by Rod »

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Re: Comparison: forcings from CO2, CH4, N2O
« Reply #99 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."
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