A week or so ago there was a New York Times article called Halting the Vast Release of Methane Is Critical for Climate, U.N. Says. As the title suggests, it was reporting on a United Nations Report that (according to the article) is likely to suggest that slashing emissions of methane, the main component of natural gas, is far more vital than previously thought.
However, when discussing carbon dioxide emissions, the article claimed that:
while it remains critical to keep reducing carbon [dioxide] emissions, which make up the bulk of our greenhouse gas emissions, it would take until the end of the century to see the climate effects.
The problem was that this was wrong. As I point out in this post, if you consider pulses of carbon dioxide emissions, then the maximum warming from such a pulse would occur after about a decade. In other words, the warming from carbon dioxide emissions peaks relatively quickly. Consequently, any emissions we avoid will have an impact on a similar timescale. Hence, it’s wrong to claim that it will take till the end of the century to see the climate effects of reductions in carbon dioxide emissions.
What was impressive was that, after I pointed this out on Twitter, the author (Hiroko Tabuchi) responded to say that they were updating the article. They changed it from it would take until the end of the century, to it will take to the second half of the century. I still don’t entirely agree, but I thought it good that they were willing to take on board the criticism and didn’t really feel like quibbling.
I did want to add, though, that I think that what is being presented in the article is potentially what Ray Pierrehumbert was warning against in this Realclimate post. As I’ve pointed out in previous posts, short-lived greenhouse gases like methane behave differently to long-lived greenhouse gases, like carbon dioxide.
The warming impact of methane emissions largely depends on how these emissions have been changing with time. In fact, if we can get methane emissions to decrease, then that would actually reverse some of the methane-driven warming. When it comes to carbon dioxide, though, how much we warm depends essentially on how much we emit in total. So, limiting carbon dioxide-driven warming requires limiting how much we emit in total, and reversing carbon dioxide-driven warming would require artificially removing carbon dioxide from the atmosphere.
There are certainly good reasons for cutting methane emissions now, and it would almost certainly have an impact on a very short timescales. However, we do need to be careful of framing this as some trade-off between reductions in methane emissions and reductions in carbon dioxide emissions. To limit long term warming requires limiting how much carbon dioxide we emit. In the absence of some kind of negative emission technology, any delay in carbon dioxide emission reductions will either commit future greaters to greater warming, or will require much more drastic emission reductions in the future.
So, I do think we should be cautious of suggesting that because reductions in methane emissions can have a large short-term climate impact that we should focus on this now, partly because it’s not the case that this isn’t true for reductions in carbon dioxide emissions, and partly because long-term warming is going to be dominated by how much carbon dioxide we emit. Of course, if there are easy ways to reduce methane emissions now, then we should do so. There may also be other reasons for reducing methane emissions now and we certainly don’t want it to continue increasing. Let’s just not forget that to limit long-term warming requires limiting how much carbon dioxide we emit.