In discussions of the greenhouse effect, carbon dioxide is the pantomime villain; the one everybody knows. However, CO2 is, by no means, the only culprit: methane (CH4) is considerably more effective as a warming agent, though unlike CO2 it has been less closely monitored. Now, a new study is helping to understand patterns of methane in the lower atmosphere.
Methane as a Greenhouse Gas
Although it has lower atmospheric concentrations than carbon dioxide, methane is around 20 times more effective in climate forcing, according to the US Climate Change Science Program. Methane has both human-induced and natural sources, being a product of the decay of organic materials under water (hence its name of ‘marsh gas’) and is associated with natural wetlands.
Methane is also a by-product of human activity – inputs which, according to Hansen, et al. ‘may be twice as great as the natural sources’ and include agricultural processes and industrial processes along with decays from human waste and other landfill.
Levels of Atmospheric Methane
Long-term records cited by the US Environmental Protection Agency (EPA), based on an assessment of air bubbles from ice cores, show that levels of the gas are currently higher than they have been for hundreds of thousands of years: there has been a significant increase (of around 150%) since preindustrial times.
Despite these estimates, it has proved difficult to track CH4 emissions with any degree of accuracy. Because of methane’s relatively short lifetime in the atmosphere, levels are subject to significant short-term fluctuations and, as noted by Zhang, et al., in research published today, there are considerable uncertainties in surface observations, although co-ordination of global data collection has been ongoing since 1983.
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