The release of a major UN report on Monday caused a spike in the level of media attention around climate change, with networks scrambling to describe the significance of the Intergovernmental Panel on Climate Change’s science assessment.
Hungry for fixes, some outlets seized on a section of the report showing that 30-50% of current warming is being caused by methane (chemical formula CH4), a greenhouse gas at least 28 times more potent than carbon dioxide in its planet-warming potential. The BBC declared that cutting methane could “buy us time” to adapt to a warming planet. Meanwhile, an item in Wired claimed governments should “start with methane” as a way of mitigating climate change.
Similar bold statements were made back in May following the release of a report from the UN Environment Programme (UNEP) which claimed “cutting human-caused methane by 45% this decade would keep warming beneath a threshold agreed by world leaders”—referring to the limits for global warming proposed in the 2015 Paris Agreement. Such emissions cuts would also prevent 255,000 premature deaths and 26 million tons of crop losses, the report stated. And while carbon dioxide stays in the atmosphere for centuries, methane breaks down within about a decade. This, the UN report said, meant “action can rapidly reduce the rate of global warming in the near-term.”
But breathlessness over the “quick fix” potential of methane is misplaced, experts say. Taking to Twitter, IPCC author Joeri Rogelj pointed out that reducing carbon dioxide and methane “are both urgent today to limit #GlobalWarming to the #ParisAgreement temperature goals and acting on methane won’t buy us time for #ClimateAction on other emissions.”
Raymond T. Pierrehumbert, Hally professor of physics at the University of Oxford, said he had similar reservations. Referring to the UNEP methane assessment, Pierrehumbert told me:
“The report gets the policy implications of the short-lived nature of methane versus the long-lived nature of carbon dioxide completely backwards. By looking just over the next few decades, methane abatement can look like an attractive option for reducing warming. However, carbon dioxide accumulates in the atmosphere over the long term, whereas methane does not, so if you look beyond a limited time frame, you see that excessive investment in methane abatement buys a short term advantage at the cost of greater, and more irreversible, warming later.”
The only way to arrest future warming, Pierrehumbert stressed, would be to bring net carbon dioxide emissions to zero as quickly as possibly.
“Moreover,” he added, “since zeroing out carbon dioxide emissions means essentially ending fossil fuel production, it automatically eliminates the associated methane emissions, and because the methane emitted while waiting for net zero dissipates quickly, this strategy would have little adverse impact on climate.”
“Until net carbon dioxide emissions are getting close to zero, methane is just a sideshow,” he said.
On the other hand, it’s not as though all methane emissions come from fossil fuels. This, said Zeke Hausfather, a research scientist at Berkeley Earth and director of climate and energy for The Breakthrough Institute, means there’s some room for nuance in the methane debate.
Firstly, Hausfather told me, “agriculture is a big part of the equation, and reducing CH4 from cows in particular is going to be a big challenge.” That will be a particular challenge because it will likely require people around the world to change their eating habits—in particular by eating much less beef.
“Second,” Hausfather said, “while methane is temporary, each ton of methane ultimately breaks down into around 2.6 tons of CO2. So while we should focus on cutting CO2, reducing methane in the near-term also has its benefits.”
Additionally, he pointed out, because the world’s oceans “buffer” the effect of greenhouse gases on surface temperatures, warming from methane can persist for decades after it is removed from the atmosphere.
Yet that still doesn’t mean methane offers a short cut to mitigating climate change.
“My takeaway is if we have to choose between prioritizing methane or CO2 reductions, we should probably prioritize CO2,” Hausfather said. “But we can proverbially walk and chew gum at the same time. Cutting methane has real climate benefits, and there is no reason not to have stronger regulations on CH4 emissions as long as it does not get in the way of also reducing CO2.”
Pierrehumbert, who was a lead author on the IPCC’s third assessment report back in 2001, came to similar conclusions in his 2014 paper ‘Short-Lived Climate Pollution,’ which warned that the benefits of an early focus on gases like methane “have been greatly exaggerated.”
He also agreed low cost methane reductions should be encouraged as long as such action did not interfere with carbon dioxide abatement.
“Many trading schemes, however, encourage such substitution, and lead to adverse climate consequences,” he noted. “Further, money invested in methane abatement from fossil fuel production is being invested in a technology that will be obsolete in a few decades, once fossil fuel production ceases, as it must if there is ever to be a halt to warming.”
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Pierrehumbert spoke about measures that should be implemented more widely to help reduce methane, noting that a considerable quantity of the gas comes from organic waste in landfills. He recommended composting, and suggested that municipal food waste collection should be made more widely available.
“Here in Oxfordshire, the food waste goes into anaerobic digesters, which produce bio-methane which is then burned to generate electricity,” he said. “As a result, you don’t just eliminate the methane emission that would have come out of landfills, you also displace the fossil fuels that would otherwise need to be burned to generate the electricity. There’s no reason that municipal composting couldn’t be done universally.”
Atmospheric methane reached record levels last year, despite an economic slowdown caused by the coronavirus pandemic, with most human-caused emissions coming from fossil fuels, waste and agriculture. But again, Pierrehumbert said this should not distract policy makers from the larger target: carbon dioxide.
“If methane emissions are increasing, it just means we have an additional thing to worry about, not that CO2 emissions—always the main act—are any less important or any less central to the efforts to stabilize climate,” he concluded.
via Forbes.com: Energy News https://ift.tt/3yJaEQX