Study calls for more action on non-CO2 greenhouse gases

Friday 12th Aug 2011 by theWeather Club

CO2 is the bogeyman of climate change, and the target of most of the major treaties on global greenhouse gas reduction. But it has been known for some time that other greenhouse gases –such as methane - measurably contribute to the problem. A new study published online today in Nature, shows that cutting emissions of those other gases could slow changes in climate that are expected in the future.

The study was born out of discussions with colleagues around the time of the 2009 United Nations’ climate conference in Copenhagen which inspired Stephen Montzka, Ed Dlugokencky and James Butler of NOAA’s Earth System Research Laboratory, to review the sources of non-carbon dioxide greenhouse gases and explore the potential climate benefits of cutting their emissions. Some of these chemicals have shorter lifetimes than CO2 in the atmosphere. Therefore cutting emissions could theoretically reduce their warming influence quite quickly, translating into real world effects in the relatively short term.

“We know that recent climate change is primarily driven by carbon dioxide emitted during fossil-fuel combustion, and we know that this problem is going to be with us a long-time because carbon dioxide is so persistent in the atmosphere,” Montzka said. “But lowering emissions of greenhouse gases other than carbon dioxide could lead to some rapid changes for the better.”

For the new analysis, the researchers considered methane; nitrous oxide; a group of chemicals regulated by an international treaty to protect Earth’s ozone layer; and a few other extremely long-lived greenhouse gases currently present at very low concentrations. The new review paper describes the major human activities responsible for these emissions, and notes that steep cuts such as 80% - as proposed by some - would be difficult. In fact without substantial changes to human behaviour, emissions of the non-CO2 greenhouse gases are expected to continue to increase.

However the climate-related benefits of reductions in non-CO2 greenhouse gases have limits, Montzka and his colleagues showed. Even if all human-related, non-CO2 greenhouse gas emissions could be eliminated today, it would not be enough to stabilize the warming influence from all greenhouse gases over the next 40 years – unless CO2 emissions were also cut significantly.

The scientists also noted in the paper the complicated connections between climate and greenhouse gases, some of which are not yet fully understood. The non-CO2 gases studied have natural sources as well as human emissions, and climate change could amplify or dampen some of those natural processes, Dlugokencky said. Increasingly warm and dry conditions in the Arctic, for example, could thaw permafrost and increase the frequency of wildfires, both of which would send more methane and carbon dioxide into the atmosphere.

“The long-term necessity of cutting carbon dioxide emissions shouldn’t diminish the effectiveness of short-term action. This paper shows there are other opportunities to influence the trajectory of climate change,” Butler said. “Managing emissions of non-carbon dioxide gases is clearly an opportunity to make additional contributions.”