Implications for mitigating methane emissions in agriculture

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.

Posted by Ken Rice on Friday, 10 September, 2021

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