The impacts of methane on climate change have been significantly underestimated, say scientists at Columbia University and NASA's Goddard Space Flight Centre. This effect is now thought to be one third higher than previous estimates.
Scientists believe that previous studies have failed to account for interactions with aerosols – fine particles suspended in the air.
The findings, published in Science, are significant because it raises the importance of measures to contain methane in strategies to combat climate change. These issues are to be discussed at the Copenhagen climate summit in December.
We've known for years that methane and carbon monoxide have a warming effect, said Drew Shindell, a climate scientist at the NASA Goddard Institute for Space Studies (GISS) and lead author of the study. But our new findings suggest these gases have a significantly more powerful warming impact than previously thought.
Shindell and colleagues used a computer simulation that couples atmospheric composition and climate together and found that interactions between gases and aerosols can significantly alter the accumulation of those gases in the atmosphere.
The researchers found that methane, in particular, has a greater impact on the atmosphere than carbon-trading schemes and global policies currently acknowledge, when one stops to consider methane's interactions with aerosols.
We found that gas-aerosol interactions substantially alter the relative importance of the various emissions. In particular, methane emissions have a larger impact than that used in current carbon-trading schemes or in the Kyoto Protocol the researchers said.
What happens is that as you put more methane into the atmosphere, it competes for oxidants such as hydroxyl with sulphur dioxide, Shindell added.
More methane means less sulphate, which is reflective and thus has a cooling effect. Calculations of GWP including these gas-aerosol linkages thus substantially increase the value for methane.
Methane is the second most significant greenhouse gas produced by human activity after carbon dioxide, responsible for about a fifth of warming effects.
Methane is described as a colourless, odourless gas with a wide distribution in nature. It is the principal component of natural gas, a mixture containing about 75% CH4, 15% ethane (C2H6), and 5% other hydrocarbons, such as propane (C3H8) and butane (C4H10). The firedamp of coal mines is chiefly methane.
Anaerobic bacterial decomposition of plant and animal matter, such as occurs under water, produces marsh gas, which is also methane.