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Carbon Brief Staff

Carbon Brief Staff

12.08.2013 | 8:35pm
ScienceCutting methane and soot alone is no quick fix for climate
SCIENCE | August 12. 2013. 20:35
Cutting methane and soot alone is no quick fix for climate

A new study says focusing efforts on cutting emissions of short-lived pollutants like methane and soot won’t offer us a quick fix for climate change.  

Even using all known measures to curb emissions of these short lived pollutants, the new modelling suggests that by 2050, global temperatures would only be 0.16 degrees Celsius lower than in a world without any climate policies.

Climate policies which tackle a range of greenhouse gases including carbon dioxide remain the best way to slow temperature rise this century, the new research concludes.

Short, sharp bursts

Carbon dioxide is the main cause of current climate change. Once released, it stays in the atmosphere for more than a thousand years, warming the planet.

Other pollutants like methane and soot also lead to warming, but are much shorter-lived in the atmosphere. Soot lasts just a few weeks and methane up to a decade, but during that time they are much more effective at trapping heat near the earth’s surface than carbon dioxide.

In recent years, a handful of studies have suggested that climate policy should focus on cutting these pollutants which cause short, sharp bursts of warming. The theory was that this could slow warming in the short term, buying extra time for cutting other greenhouse gases like carbon dioxide.

One such study by the United Nations Environment Programme said half a degree Celsius could be shaved off expected warming by mid-century by cutting methane and soot emissions alone. This led international policymakers to form a coalition dedicated to tackling these short-lived pollutants.

A modest difference

But new research finds such a dramatic climate benefit is unlikely. It suggests that going all-out to reduce methane and soot emissions between 2015 and 2035 would make a relatively modest difference to the amount of warming we can expect by 2050, with global mean temperatures only 0.16 degrees Celsius lower than they would have been in world with no climate policies.

And achieving those drastic emissions reductions wouldn’t be easy. Achieving the required methane cuts would mean capturing the gas as it escapes from landfills, coal mines, and the processes associated with natural gas extraction.

Cutting soot levels would mean completely phasing out the use of wood and coal for heating and cooking worldwide. It would also require much stricter controls on pollution from cars and larger vehicles across all regions.

These are quite challenging measures, and implementing them all may not be “strictly achievable”, say the authors. That means the actual climate benefit could well be smaller.

Back to Plan A?

The authors of the study suggest a more comprehensive climate plan to cut a range of greenhouse gases would have a much bigger effect on limiting temperature rise – both in the near term and the long term.

Lead author, Steven Smith, explained:

“If we want to stabilize the climate system, we need to focus on greenhouse gases such as carbon dioxide, nitrous oxide and methane. Concentrating on soot and methane alone is not likely to offer much of a shortcut.”

In another part of their study, the authors looked instead at the effect of curbing a wide range of greenhouse gases according to a low emissions pathway used by the Intergovernmental Panel on Climate Change. This scenario included significant cuts to methane, but only limited cuts to soot emissions.

Again, the authors calculated how much lower temperature rise would be compared to a world with no climate policies. Their modelling showed that by 2050, broad emissions cuts across a range of greenhouse gases were much more effective at limiting temperature rise than focusing on deep, fast cuts in only methane and soot emissions.

The authors conclude that while targeting powerful warming agents can have some climate benefits, comprehensive climate policies which aim to reduce both long and short lived greenhouse gases should “remain the central focus of any climate-mitigation policy that aims to stabilize the climate system”.

Where next for climate policies?

Cutting short-lived but powerful greenhouse gases like methane and soot levels might appear to be a useful quick approach to limiting warming. There would also be some important advantages – the health benefits from reducing soot emissions, for example.

But this new research suggests the temperature cuts offered by climate policies which focus only on short-lived warming pollutants like soot and methane are “relatively modest”. Cutting emissions of a wide range of greenhouse gases and warming pollutants looks like a much better way to slow temperature rise through to 2050 and beyond.

 

Smith, S.J. & Mizrahi, A. (2013) Near-term climate mitigation by short-lived forcers. Proceedings of the National Academy of Sciences. DOI: 10.1073/pnas.1308470110 


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