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Author Topic: Comparison: forcings from CO2, CH4, N2O  (Read 19213 times)

Ned W

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Re: Comparison: forcings from CO2, CH4, N2O
« Reply #100 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, 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.

Ned W

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Re: Comparison: forcings from CO2, CH4, N2O
« Reply #101 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.

AbruptSLR

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Re: Comparison: forcings from CO2, CH4, N2O
« Reply #102 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."
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
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Ned W

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Re: Comparison: forcings from CO2, CH4, N2O
« Reply #103 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):


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:


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.  CMIP5 RCPs are here.


sidd

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Re: Comparison: forcings from CO2, CH4, N2O
« Reply #104 on: August 24, 2018, 11:50:01 PM »
Thanks Mr. Ned W. Very clear.

sidd

AbruptSLR

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Re: Comparison: forcings from CO2, CH4, N2O
« Reply #105 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)."

« Last Edit: August 25, 2018, 12:47:50 AM by AbruptSLR »
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AbruptSLR

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Re: Comparison: forcings from CO2, CH4, N2O
« Reply #106 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
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
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Ned W

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Re: Comparison: forcings from CO2, CH4, N2O
« Reply #107 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...
« Last Edit: August 25, 2018, 03:00:31 AM by Ned W »

Ned W

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Re: Comparison: forcings from CO2, CH4, N2O
« Reply #108 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.)
« Last Edit: August 25, 2018, 04:15:18 AM by Ned W »

sidd

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Re: Comparison: forcings from CO2, CH4, N2O
« Reply #109 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

AbruptSLR

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Re: Comparison: forcings from CO2, CH4, N2O
« Reply #110 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.

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AbruptSLR

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Re: Comparison: forcings from CO2, CH4, N2O
« Reply #111 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
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
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Ned W

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Re: Comparison: forcings from CO2, CH4, N2O
« Reply #112 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. 


AbruptSLR

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Re: Comparison: forcings from CO2, CH4, N2O
« Reply #113 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.
« Last Edit: August 25, 2018, 07:36:51 PM by AbruptSLR »
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Ned W

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Re: Comparison: forcings from CO2, CH4, N2O
« Reply #114 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.

TerryM

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Re: Comparison: forcings from CO2, CH4, N2O
« Reply #115 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

Ned W

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Re: Comparison: forcings from CO2, CH4, N2O
« Reply #116 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. 

AbruptSLR

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Re: Comparison: forcings from CO2, CH4, N2O
« Reply #117 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.
« Last Edit: August 26, 2018, 01:18:58 AM by AbruptSLR »
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sidd

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Re: Comparison: forcings from CO2, CH4, N2O
« Reply #118 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


AbruptSLR

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Re: Comparison: forcings from CO2, CH4, N2O
« Reply #119 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
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Re: Comparison: forcings from CO2, CH4, N2O
« Reply #120 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.
« Last Edit: August 26, 2018, 02:18:39 AM by TeaPotty »

sidd

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Re: Comparison: forcings from CO2, CH4, N2O
« Reply #121 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

Ned W

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Re: Comparison: forcings from CO2, CH4, N2O
« Reply #122 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:



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.

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Re: Comparison: forcings from CO2, CH4, N2O
« Reply #123 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.

 :-\

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Re: Comparison: forcings from CO2, CH4, N2O
« Reply #124 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. 


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Re: Comparison: forcings from CO2, CH4, N2O
« Reply #125 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.
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Re: Comparison: forcings from CO2, CH4, N2O
« Reply #126 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



 
« Last Edit: August 26, 2018, 07:11:44 AM by sidd »

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Re: Comparison: forcings from CO2, CH4, N2O
« Reply #127 on: August 26, 2018, 09:47:50 AM »
The CO2 forcings were lower in those two periods? Unprecedented actions might well have unprecedented reactions?

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Re: Comparison: forcings from CO2, CH4, N2O
« Reply #128 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.


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Re: Comparison: forcings from CO2, CH4, N2O
« Reply #129 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.
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Re: Comparison: forcings from CO2, CH4, N2O
« Reply #130 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.

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Re: Comparison: forcings from CO2, CH4, N2O
« Reply #131 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.
« Last Edit: August 26, 2018, 02:13:47 PM by TeaPotty »

Ned W

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Re: Comparison: forcings from CO2, CH4, N2O
« Reply #132 on: August 26, 2018, 02:11:23 PM »
A reminder:



Things may change in the future, but right now the impact of current methane concentration is relatively small compared to CO2.

Ned W

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Re: Comparison: forcings from CO2, CH4, N2O
« Reply #133 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".

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Re: Comparison: forcings from CO2, CH4, N2O
« Reply #134 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


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

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Re: Comparison: forcings from CO2, CH4, N2O
« Reply #135 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:


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Re: Comparison: forcings from CO2, CH4, N2O
« Reply #136 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."
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TeaPotty

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Re: Comparison: forcings from CO2, CH4, N2O
« Reply #137 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.

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Re: Comparison: forcings from CO2, CH4, N2O
« Reply #138 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.
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Re: Comparison: forcings from CO2, CH4, N2O
« Reply #139 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?

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Re: Comparison: forcings from CO2, CH4, N2O
« Reply #140 on: August 26, 2018, 07:58:48 PM »
Agreed, no need for this tone.
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Re: Comparison: forcings from CO2, CH4, N2O
« Reply #141 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.
« Last Edit: August 26, 2018, 08:13:09 PM by TeaPotty »

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Re: Comparison: forcings from CO2, CH4, N2O
« Reply #142 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.

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Re: Comparison: forcings from CO2, CH4, N2O
« Reply #143 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.

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Re: Comparison: forcings from CO2, CH4, N2O
« Reply #144 on: August 27, 2018, 02:27:57 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.

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) I say

Quote
One of the authors, Dr Michelle Cain, explains in , 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, 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 mentioned below

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

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Re: Comparison: forcings from CO2, CH4, N2O
« Reply #145 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.


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Re: Comparison: forcings from CO2, CH4, N2O
« Reply #146 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.
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Re: Comparison: forcings from CO2, CH4, N2O
« Reply #147 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."
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson

AbruptSLR

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Re: Comparison: forcings from CO2, CH4, N2O
« Reply #148 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.
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AbruptSLR

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Re: Comparison: forcings from CO2, CH4, N2O
« Reply #149 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, 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.
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson