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Implications for mitigating methane emissions in agriculture

Posted on 10 September 2021 by ATTP

This is a re-post from And Then There's Physics

Since I was discussing methane in yesterday’s post, I thought I would highlight a paper on [u]nderstanding the implications for mitigating methane emissions in agriculture (H/T Miles King). The reason I found it interesting, is that it uses GWP* (which I try to explain here), rather than the more standard GWP100, or GWP20, metrics.

The results are nicely explained at the beginning of the paper. When considering agricultural emission scenarios from 2020-2040:

  • A sustained ~0.35% annual decline is sufficient to stop further increases in global temperatures due to agricultural CH4 emissions. This is analogous to the impact of net-zero CO2 emissions.
  • A ~5% annual decline could neutralize the additional warming caused by agricultural CH4 since the 1980s.
  • Faster reductions of CH4 emissions have an analogous impact to removing CO2 from the atmosphere.

What this illustrates is that fairly modest reductions in agricultural methane emissions (~0.35% per year) can largely stop future agricultural methane-driven warming, stronger methane emission reductions (~5% per year) can reverse the agricultural methane-driven warming since about 1980, and even faster reductions would be analagous to negative CO2 emissions.

The reason these results might seem at odds with previous estimates is that GWP* better estimates methane-driven warming than GWP100, or GWP20.

However, even though modest methane emission reductions can have a big impact on future methane-driven warming, the paper also points out that...

a 1.5% annual increase in CH4 emissions would lead to climate impacts about
40% greater than indicated by GWP100.

In other words, if methane emissions continue to increase, then they will lead to substantial future warming, which the standard metrics may under-estimate (GWP100, at least).

Also, even though this indicates that modest reductions in methane emissions can have a substantial impact, the remaining carbon budget for 1.5C is small enough that if we really do want a good chance of limiting warming to 1.5C, then we’d probably still need to make substantial cuts to methane emissions, along with rapidly reducing CO2 emissions. However, I do still think it’s worth pointing out that even modest reductions in methane emissions can have a big impact on future methane-driven warming.

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Comments

Comments 1 to 6:

  1. ATTP, very interesting article. How would the average reader apply this to their own mitigation goals? If a person normally ate 100 hambugers/yr, with respect to mitigation of methane emissions only, could they feel like they were doing their part to stabilize the climate at the current temperature by eliminating 1 hamburger from their diet over a 3-yr period (a reduction of about 0.33%)? The next 3-yr period they would eliminate a second hamburger, etc. A person drinking 1 cup milk/day would have to skip 1 cup of milk the first year, then 2 cups the second year, etc. I realize my examples are simplistic and assumes that everything is held constant, but ultimately we need to put this in terms that people can digest (pun intended).

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  2. Evan @1 :

    regarding hamburgers, your 100/year mathematical logic is irrefutable.  But will the 100-per-year man's offspring be agreeable to continuing the monotonic [pun intended] diet reduction?

    Perhaps a faster CH4 draw-down might be achieved by focusing your persuasive efforts on a high-consuming sub-group, such as ex-Presidents who (allegedly) have a subsistence diet of 100 hamburgers per month (an observed MAC or Mean Average Consumption).  Such people would reach their personal-mitigation goal in just 25 years.

    However, we would need to brace ourselves for the political heartburn when, in the 301st month, the high-consuming individuals open their meal-package to find a nothing-burger [bun unintended].

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  3. Eclectice @2

    Yes, more would need to be done. I was trying, as a first step, to digest the information in ATTP's post, because these numbers are new to me.

    The danger I see in my math is that it propogates the idea that we will easily stabilize climate. I find the paper cited in this post interesting, but the problem, as with many other studies, is that it assumes all other things don't change. What this article really shows is just how sensitive our climate is to CH4. So if we all reduce our hamburger intake by 1/yr or so, but if natural CH4 emissions increase to more than compensate, we have a problem. As this article points out, a really big problem. However, the average person will make a modest change to their diet, thinking we are now OK. But with natural emissions likely to increase, and with global population continuing to increase, it will likely take more than eating one less hamburger/year to really make a difference.

    But the first task was to make sure I understood the ideal math, before embarassing myself with my related thoughts.

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  4. Eclectic@2

    Sorry for mispelling your "name". No way to correct mistakes. :-(

    Nice "bun pun". Missed that on first read.

    Agree that offspring will likely protest inheriting a burger-reduced diet. They will no doubt argue to have their lives recapitalized at 100 burgers/year so that they can more easily show progress, without ever being required to make a difference. Tough problem this is getting rid of GHG's.

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  5. Evan @ 3&4 :

    Quite so.  And getting rid of anthropogenic GHG's will be a slow business ~ much slower than by 2050,  I fear.  We will likely muddle through, eventually, to a warmer "nett-zero-carbon" world having rather worse than today's conditions.  Worse in several ways.

    Like you, I am somewhat dubious about the practical efficacy of ATTP's methane-reducing suggestion ~ though I confess the matter is indeed beyond my Ken (but not beyond his).   Still, as the Scots say: Many a mickle makes a muckle.   (My own non-vegan contribution runs to phasing veal schnitzel into pork schitzel.  Having no political ambitions in the Grand Oral Party, I eschew hamburgers.)

    Evan, please do not be too concerned about committing obvious typo errors.  In one way, it is regrettable that the SkS posting system does not allow past errors to be corrected . . . yet in another way it is an object lesson ~ a metaphor for Life as she is lived.  (Note: if you have committed a truly egregious typo which misinforms/misleads the reader, then you may ask the Moderator to edit/correct your mistake.  Of course, you would not wish to be frequently invoking the Deus-ex-machina.)

     

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  6. And . . . Evan, as you see, I won't ask the Moderator to correct my (possibly Freudian slip) typo re the pork schnitzel.  I do rather prefer the beef.

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    Moderator Response:

    [BL]

    I had to look more than once to see the typo.

    As requested, we will leave it intact.

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