There was an article a couple of days ago about why the climate emergency is now the methane emergency. I appreciate that the general argument is about limiting future warming, but some of what is suggested is essentially wrong.
For example, it says we’re facing tipping points which could trigger runaway warming, which is simply wrong. A true runaway is essentially impossible in our current climate state. The albedo is too high and the sun is too faint. We could trigger some feedbacks that would amplify the warming, and these are expected to become more significant the more we warm. However, if we start to reduce emissions soon and get to (net) zero by around mid-century, then – although these may still be important – they may not be all that significant. I wrote a post a while ago that tried to explain the difference between feedbacks, runaway, and tipping points.
The article then goes on to say
Even rapidly accelerating the end of fossil fuel burning will not slow warming in a timeframe relevant to this threat……….
To slow warming we must keep our focus on cutting CO2 but now also focus intensely on the shorter lived, far more potent gases such as methane.
The science explains this. Whereas CO2 drives warming slowly over a century, methane drives warming quickly – in around a decade.
I agree that we should keep our focus on CO2 and also focus on the shorter-lived species, such as methane. However, the claim that CO2 drives warming slowly over a century is wrong. Peak warming from a pulse of CO2 actually occurs after about a decade. Hence, reductions in CO2 emissions will occur on a similar timescale. Hence, we should be careful of thinking that dealing with short-term warming requires a more intense focus on methane, rather than on CO2.
The article then goes on to suggest that the warming potential of methane over a period of 10 years is 90-115 times that of CO2. What this is referring to is the global warming potential (GWP) and it is indeed the case that this is much greater for methane than for CO2. However, it doesn’t quite mean what the article implies.
How much warming we get from methane emissions depends on how they’ve been changing. If emissions are going up, then this will result in warming. However, if they’re constant there should be little additional warming. If they’re going down, then some past warming will actually be reversed. So, methane does indeed have a much higher GWP than CO2 over a timescale of decades, but this doesn’t necessarily mean that methane emissions will drive much more warming than CO2 emissions. If you want to understand why this is, I tried to explain it in this post, and this Carbon Brief article by Michelle Cain is also very good.
Essentially, as long as we are emitting CO2 there will be CO2-driven warming, which will only stop (but not reverse) when CO2 emissions go to zero. Warming due to methane, on the other hand, will mostly stop if we get methane emissions to stabilise, and will reverse if we get methane emissions to go down. Given the differences between methane-driven, and CO2-driven warming, how much we will eventually warm depends mostly on how much CO2 we end up emitting.
Of course, this doesn’t mean that we shouldn’t worry about methane emissions. According to the latest IPCC report, methane accounts for a reasonable fraction of the warming we’ve experienced and, since methane emissions are still increasing, will contribute substantially to future warming. If we want to meet the Paris targets, then we will need to deal with both methane and CO2 emissions, especially if we don’t want any overshoot.
However, we do need to be careful of thinking that limiting short-term warming means focussing on methane. As pointed out in this Realclimate post, the long atmospheric lifetime of CO2 means that any delays to CO2 emission reductions are likely to commit future generations to warming that is difficult to reverse and could have been avoided. Methane’s short atmospheric lifetime means that delays to methane emission reductions don’t carry the same risk.
This doesn’t mean, though, that near-term methane emission reductions aren’t important (they are if we want to meet current targets without temperature overshoots). The main point is to be careful of thinking that focussing on methane now can buy us time (it doesn’t) or that it’s now essentially become a methane emergency (it hasn’t).
Why the Climate Emergency is now a Methane Emergency – article in resilience.
Feedbacks, runaways, and tipping points – post I wrote trying to explain these different issues.
Losing time, not buying time – Realclimate post explaining why focussing on methane emission reductions doesn’t really buy us time.
Methane – other posts I’ve written trying to explain the differences between methane and CO2.
A new way to assess ‘global warming potential’ of short-lived pollutants – nice Carbon Brief article by Michelle Cain presenting a new way to quantify the GWP of short-lived pollutants.