Climate change: A nasty surprise in the greenhouse

Methane is a potent greenhouse gas — per molecule, more than 20 times as powerful as carbon dioxide1. Moreover, when methane emissions rise, so too does the concentration of the pollutant ozone in the troposphere, the lowest layer of Earth's atmosphere2. Methane also consumes hydroxyl radicals, whose oxidative effects are essential to atmospheric cleansing. On page 439 of this issue [of Nature], Bousquet et al. recount the results of an international effort to measure atmospheric methane concentrations and combine these data with a computer model of atmospheric chemistry and transport. The bad news is that the slowdown in global methane emissions in the past few decades was only temporary: reports of the emissions' control have been exaggerated.


At present, about two-thirds of global methane comes from anthropogenic sources, and most emissions occur in the Northern Hemisphere (Fig. 1). Of naturally produced methane, the largest proportion stems from bacteria in wetlands that produce the gas when decomposing organic material. The growth rate of atmospheric methane was more than 10% per decade before 1980, but by the 1990s it had dropped to nearly zero (Fig. 2). Bousquet and colleagues compute the global methane source distribution, especially its variability over recent decades. This is a rather controversial issue, as it is difficult to determine whether this variability should be attributed to fluctuations in the sources or in the sinks; the sink mechanisms are dominated by the good offices of the atmospheric hydroxyl radicals.


from Nature