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# Why was there a "plateau" from around 1999 to 2007 in methane values?

edited March 2015

I opened up this thread because I think that finding out what happened here might be rather important. The plateau seems to be at least partially correlated with the socalled "global warming pause", where there may however be discorrelations due to incomplete temperature data, especially after the year 2007 (it should also be pointed out that hte density of methane measuring stations is likewise suboptimal). The correlation between methane and temperature data had been also found for global anomalies and their averaged annual differences (diff12). It is not clear wether methane values precede temperature values or not, or both. If not then a cause could be that higher temperatures may lead to higher methane releases like from melting permafrost. If yes then a reason might be that methane might have a bigger global warming potential than assumed (it is not clear wether a UV absorption line in the methane spectrum was appropriately taken into account). At least partially also both mechanisms or others may take place - the question here is then which influence dominates.

The methane plateau and its correlation with temperatures seems to be a rather important component in establishing this question. It should also be mentioned that global C02 doesn't show this strong plateau. In 2003 (so to say in the middle of the plateau the article"Atmospheric methane levels off: Temporary pause or a new steady state?" was outlining in the abstract:

The globally-averaged atmospheric methane abundance determined from an extensive network of surface air sampling sites was constant at ~1751 ppb from 1999 through 2002. Assuming that the methane lifetime has been constant, this implies that during this 4-year period the global methane budget has been at steady state. We also observed a significant decrease in the difference between northern and southern polar zonal annual averages of CH4 from 1991 to 1992. Using a 3-D transport model, we show that this change is consistent with a decrease in CH4 emissions of ~10 Tg CH4 from north of 50�N in the early-1990s. This decrease in emissions may have accelerated the global methane budget towards steady state. Based on current knowledge of the global methane budget and how it has changed with time, it is not possible to tell if the atmospheric methane burden has peaked, or if we are only observing a persistent, but temporary pause in its increase.

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1.

Methane has a much shorter transient lifetime, or residence time, in the atmosphere in comparison to CO2. For that reason, it will more readily show variations over time, whereas CO2 will continue its upward trend as it gets convolved against a fat-tail diffusional sequestration response.

Comment Source:Methane has a much shorter transient lifetime, or residence time, in the atmosphere in comparison to CO2. For that reason, it will more readily show variations over time, whereas CO2 will continue its upward trend as it gets convolved against a fat-tail diffusional sequestration response. 
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2.

1999 was a peak year for a CH4 emissions spike and a peak in CH4 emission rate so a very bad starting year for any trend. I'll add a couple of graphs tomorrow when I've worked out how to post .png files correctly.

Comment Source:1999 was a peak year for a CH4 emissions spike and a peak in CH4 emission rate so a very bad starting year for any trend. I'll add a couple of graphs tomorrow when I've worked out how to post .png files correctly.
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3.

Jim, That would be instructional if you can correlate estimated CH4 emissions with atmospheric concentration. At least part of the increase in emissions would be due to an increase in CH4 outgassing with elevated temperatures.

You might even be able to infer the residence time.

Comment Source:Jim, That would be instructional if you can correlate estimated CH4 emissions with atmospheric concentration. At least part of the increase in emissions would be due to an increase in CH4 outgassing with elevated temperatures. You might even be able to infer the residence time. 
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4.
edited March 2015

That would be instructional if you can correlate estimated CH4 emissions with atmospheric concentration.

I presumed that emission volumes were calculated from atmospheric sample concentrations? Do you mean computer model estimates?

Nad and I can't even get temp data for 3 antarctic stations atm.

Not employing code librarians (who obviously also do data) is still one of the big "tyranny of structurelessness" immaturities of the IT industry and especially FOSS.

Comment Source:> That would be instructional if you can correlate estimated CH4 emissions with atmospheric concentration. I presumed that emission volumes were calculated from atmospheric sample concentrations? Do you mean computer model estimates? Nad and I can't even get temp data for 3 antarctic stations atm. Not employing code librarians (who obviously also do data) is still one of the big "tyranny of structurelessness" immaturities of the IT industry and especially FOSS.
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5.
edited March 2015

Jim, By correlation I was thinking in comparison to something like CO2. One can get CO2 concentrations from atmospheric readings, i.e. @MaunaLoa. These are correlated to estimates derived from fossil fuel emissions -- i.e. every barrel of oil combusted will add X amount of CO2 to the air (given some fraction will diffusionally sequester). Since we have adequate estimates of total fossil fuel consumption, this correlation turns out to be very effective year-over-year.

Now, for methane, this correlation may be problematic. Estimates of methane production from livestock is probably a guess. Same with estimates from organic decomposition. That fraction due to incomplete combustion of fossil fuels and leakage/loss is probably better estimated. However, this mix of sources of methane makes it harder to get as good a correlation for methane as with CO2.

This is an ongoing issue in estimating climate sensitivity of GHGs. The "skeptics" of AGW beat climate scientists over the head on not being able to estimate contributions of various GHGs and of the poorly characterized aerosols and particulates.

Comment Source:Jim, By correlation I was thinking in comparison to something like CO2. One can get CO2 concentrations from atmospheric readings, i.e. @MaunaLoa. These are correlated to estimates derived from fossil fuel emissions -- i.e. every barrel of oil combusted will add X amount of CO2 to the air (given some fraction will diffusionally sequester). Since we have adequate estimates of total fossil fuel consumption, this correlation turns out to be very effective year-over-year. Now, for methane, this correlation may be problematic. Estimates of methane production from livestock is probably a guess. Same with estimates from organic decomposition. That fraction due to incomplete combustion of fossil fuels and leakage/loss is probably better estimated. However, this mix of sources of methane makes it harder to get as good a correlation for methane as with CO2. This is an ongoing issue in estimating climate sensitivity of GHGs. The "skeptics" of AGW beat climate scientists over the head on not being able to estimate contributions of various GHGs and of the poorly characterized aerosols and particulates. 
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edited March 2015

I can put only a couple of numbers for gas leakage from distribution networks. A first Boston sampling study a few years ago claimed 7% leakage and a more recent one appears to have revised this to 1-2% iirc. I've tried to get the figures for British Gas but even though I worked in the same building where gas suppliers and DECC reps meet they're only concerned about theft and swathes of incorrect or missing meters.

What's a sensible equation for what you're suggesting?

methane warming = total warming - fossil fuel CO2 - organic CO2 +/- ?

Comment Source:I can put only a couple of numbers for gas leakage from distribution networks. A first Boston sampling study a few years ago claimed 7% leakage and a more recent one appears to have revised this to 1-2% iirc. I've tried to get the figures for British Gas but even though I worked in the same building where gas suppliers and DECC reps meet they're only concerned about theft and swathes of incorrect or missing meters. What's a sensible equation for what you're suggesting? methane warming = total warming - fossil fuel CO2 - organic CO2 +/- ?
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Jim, I don't have any good ideas. What I go with is use CO2 as a "leading indicator" and assume that the other GHGs scale with it. If you come up with something, kudos as it is a difficult problem to unscramble. Especially in terms of doing any kind of multiple linear regression for how they compose, as the other GHGs are effectively co-linear and end up creating degeneracies in the solution.

Comment Source:Jim, I don't have any good ideas. What I go with is use CO2 as a "leading indicator" and assume that the other GHGs scale with it. If you come up with something, kudos as it is a difficult problem to unscramble. Especially in terms of doing any kind of multiple linear regression for how they compose, as the other GHGs are effectively co-linear and end up creating degeneracies in the solution.