a global methane pledge is great – but only if it doesn’t distract us from CO₂ cuts

The US President Joe Biden and the President of the European Commission, Ursula von der Leyen, have launched an alliance that includes more than 100 countries. the Global Methane Pledge – an agreement to cut methane emissions by 30% between 2020 and 2030.

Methane is a greenhouse gas which has caused about 0.5°C of global warming, according to the latest assessment by the Intergovernmental Panel on Climate Change. Each molecule that is added to the atmosphere has a value of about 26 times more potent at warming than a CO₂ molecule, but only remains in the atmosphere for about a decade. Methane can leak from oil and natural gas wells, landfills, or is leaked by livestock. The agreement covers two-thirds the global economy as well as half the top 30 methane emitters (including Brazil). Russia, India, China and China have not signed the agreement at the time this article was written.

For the past ten years, I have been working on methane emissions and their impact on climate change. The atmospheric levels of methane have risen rapidly over the past decade, which has led to more global warming. It would be wonderful to reduce methane emissions by 30% before 2030. But what about that little voice in my head?

It’s the suspicion that so much noise about methane cuts will (deliberately or not) be a good news story that obscures slow progress on CO₂ emissions. This might make you wonder: Is this a problem? Isn’t any action to be applauded? Yes, and no. Yes, because any reduction in greenhouse gas emissions is progress towards the Paris Agreement’s temperature goals. It is indisputable. No, if it displaces effort away from the main driver of global warming – fossil CO₂ emissions.

We may not know how much displacement is happening, but we do know that for the past 30 years, since the Rio Earth Summit, the world has failed to reduce CO₂ emissions. And so, because we have effectively left it too late to have a smooth reduction in CO₂ emissions down to zero while limiting warming to well below 2°C, we hope that perhaps methane is going to save our bacon.

How can methane reductions be so much more effective than CO₂ reductions, when methane contributes less to global warming than CO₂? It’s because methane is much shorter-lived in the atmosphere than CO₂, and therefore reducing emissions of methane actually reduces the amount of methane in the atmosphere within decades. Methane has a half life of approximately a decade. This means that if you emit 10 tons of methane now, 5 tonnes will remain in atmosphere after a decade. The methane-caused global heat rise would be halved if we stopped emitting methane completely in 20 years. This is in stark contrast to CO₂, which lives for so long in the climate system that even with no emissions at all, the CO₂-caused global warming will remain the same for centuries.

So this makes it quite clear that all the way along on the pathway to net-zero CO₂ emissions, our ever-diminishing annual CO₂ emissions are causing additional warming, which will remain for hundreds of years. This is why slow progress on CO₂ is so damaging. Every tonne of CO₂ we emit will stay in the climate system, warming the planet, for hundreds, potentially even thousands, of years.

Are you looking for long-term wins?

Methane emissions reductions can be a quick win, slashing global warming by just a few tenths. However, this decrease in temperature is proportional with the rate at which methane emission reductions occur. When the reductions cease (e.g. If global methane emissions are stabilized at 30% below 2020 levels, then methane-caused heating will stabilise and then slowly rise again. The reason is that while the atmosphere reacts quickly to changes in greenhouse gases (in a few years), deep oceans respond much slower. The whole climate system would take hundreds of years to equilibrate to changes, and so if we “froze” the atmospheric composition, temperature would slowly rise over centuries. If we could reduce methane emissions by about 3-5% per year after 2030, this would counter the slow equilibration and provide a stable level. methane-caused global warming.

Two distinct conclusions can be drawn from the same basic science: Methane emissions reductions do not bring down temperature in the near-term.

Position one is that cutting methane emissions produces results faster than cutting CO₂ emissions, and therefore we should do this to put the handbrake on global warming. This argument focuses on the immediate goal of limiting global warming. However, if limited funds are spent on methane cuts instead of CO₂ cuts (such as by a company with a set budget for emission reduction projects) then temperatures will be lower in the short term but higher in the long term.

Position two is therefore that we should prioritise CO₂ cuts over methane cuts. The cumulative nature of CO₂ means that if we reach net zero in 2050 with rapid action starting from 2025, we will have lower sum-total CO₂ emissions and therefore lower temperatures than if we delay even longer and only start reducing emissions in 2035. All efforts should go towards CO₂ reductions, and until we are confident we are on track with CO₂, there is no time to waste on methane.

These two conclusions are based upon the same science. It is the surrounding assumptions – whether we can act on two fronts at once, or if action on methane inevitably detracts from actions on CO₂, whether we should prioritise near-term warming so society can adapt to a slightly more gradual change in climate, whether by 2100 we will have cracked carbon removal and storage so we can remove all the CO₂ later?

These are discussions that go way beyond the climate science, which is why it is great that methane is having its day at COP26 – so long as the political discussions are based on a solid foundation of the science, so that the consequences of any decisions are understood.

These contradictory views may seem confusing but there’s one thing that can be agreed upon. Fossil fuels account for about a third anthropogenic methane emission. The Global Methane Pledge could be implemented if fossil extraction and use were stopped by 2030. This would also eliminate most anthropogenic CO2 emissions. It’s that simple.