London: A new study has led climate modelers to determine that an aerosol-laden sky could make methane a more potent greenhouse gas than previously thought.
According to a report in Nature News, the study was conducted by Drew Shindell from NASA Goddard Institute for Space Studies, New York, and colleagues.
They ran a range of computerized models to show that methane’s global warming potential is greater when combined with aerosols — atmospheric particles such as dust, sea salt, sulphates and black carbon.
The International Panel on Climate Change (IPCC) and treaties such as the Kyoto Protocol assume methane to be, tonne-for-tonne, 25 times more potent than carbon dioxide at warming the planet.
But, the interaction with aerosols bumps up methane’s relative global warming potential (GWP) to about 33, though there is a lot of uncertainty around the exact figure.
Shindell said that climate policy-makers need to pay much more attention to restricting short-lived pollutants, such as methane, carbon monoxide, volatile organic compounds (VOCs) and aerosols.
This could create significant changes in the local and global climate quite quickly, he says, whereas the effects of efforts to reduce emissions of long-lived carbon dioxide will not be seen for many years.
“The short-lived things are really powerful,” said Shindell.
The increased influence attributed to methane is interesting, according to Frank Dentener, from the European Commission``s Institute for Environment and Sustainability, Ispra, Italy.
Dentener said that cutting methane emissions often doesn’t cost anything and can actually end up making money — by collecting the gas to sell, or by saving emissions in making a process more efficient and cheaper.
Methane, aerosols and other short-lived pollutants have a complicated chemical relationship, only some of which Shindell’s models could capture.
For example, methane leads to increased formation of ozone in the troposphere, which can reduce agricultural yields.
It is also eventually oxidized to carbon dioxide; or by other chemical reactions can form water vapour - also a greenhouse gas - in the stratosphere.
In yet another example, methane’s reaction with hydroxyl reduces the amount of that chemical available to create cooling sulphate aerosols.
“Instead of looking at single components, they look in much greater details at what emissions of these components will do to a whole sequence of things,” said Dentener.