After almost a decade of stability, the amount of methane in the atmosphere has been growing since the start of 2007, according to measurements taken by two global monitoring networks, AGAGE and CSIRO.
The findings are cause for concern because methane is many times more powerful than carbon dioxide as a greenhouse gas, and has so far accounted for about a fifth of the human contribution to climate change. Matthew Rigby of the Massachusetts Institute of Technology in Cambridge and their co-workers write that, by late 2007, the proportion of methane in the atmosphere was rising by 10 parts per billion per year at all monitoring stations around the world.
High bacterial methane emissions from wetlands in an unusually warm Siberia seem to have played some part in the northern hemisphere increase. The authors also suspect that an unproven drop in hydroxyl free radicals could be driving the trend.