Scientists want re-calculation of how emissions such as methane cause global warming

Scientists want re-calculation of how emissions such as methane cause global warming
Scientists at Oxford University recommend an alternative method of calculating how emissions such as methane cause global warming.

Scientists at Oxford University have spelled out how the immediate global temperature impacts of increasing and decreasing livestock numbers are undervalued, and the impact of numbers remaining stable is overvalued.

They said the different lifespans of emissions are crucial to understanding their potential to warm the earth’s atmosphere.

Carbon dioxide is an extremely long-lived gas, and accumulates in the atmosphere for as long as emissions are maintained.

Even if CO2 emissions were to cease, the warming they caused would remain relatively fixed for centuries.

“Short-lived” climate pollutants such as methane do not accumulate, thanks to their relatively rapid natural removal from the atmosphere. After causing an initial temperature rise, a sustained level of methane emissions does not cause significant continued warming.

However, this cannot be captured by the GWP100 method used to calculate how different emissions contribute to global temperature change.

Researchers from the Livestock, Environment and People project at the Oxford Martin School warned the GWP100 method obscures how different emissions contribute to global temperature change, and could put at risk efforts to limit global warming.

“This has important implications for how countries work out emissions targets for different sectors,” said Dr John Lynch, lead author of the projects’s latest research paper, published in the Environmental Research Letters peer-reviewed open-access scientific journal.

The authors recommend an alternative method of calculating how emissions cause global warming, called GWP*.

Dr John Lynch said, “We can’t afford to get the maths wrong on this."

Co-author Dr Michelle Cain said: “Reducing net CO² emissions to zero is crucial to preventing further temperature rises. But the current accounting significantly underestimates the impact of increasing methane emissions, which is what’s happening at present.

“Any policy decisions which increase methane from agriculture or industry would be extremely detrimental to achieving the Paris Agreement temperature goal.”

Another co-author, Halley Professor of Physics at the University of Oxford, Raymond T Pierrehumbert, said: “In order to make sound moral judgements, one must have an accurate assessment of the consequences of various actions. The standard metrics of methane and other short-lived greenhouse gases simply do not do the maths right. They get both the short term and long term impacts wrong by substantial amounts, and are not a sound basis for planning public policy.”

The Oxford Martin School is a research and policy unit based in the Social Sciences Division of the University of Oxford.

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