While the ubiquitous attention on carbon dioxide— after decades of assumed harmlessness—has prompted it to be heat-trapping public enemy number one. But  the fact remains that three other gasses make significant contributions to global warming as well. Water vapor, nitrous oxide, and methane, the last of which is 25 times more potent than CO2, and responsible for roughly 20% of the warming experienced in the 20th Century.

Methane levels had been relatively steady for the past decade or so—in stark contrast to still accelerating carbon dioxide concentrations—but a new report suggests those levels may again be climbing. It is disturbing enough to see such a potent heat-trapper jump, but the really scary part is that scientists don't really know why it's gone up so suddenly.

Methane is created from a tremendous variety of sources, from cattle dung, to natural decomposition of plant matter, to leaky natural gas containers. However, the simple hydrocarbon is fairly volatile, and the lack of accumulation in recent years had led experts to believe it was being broken down at a rate roughly equal to its production. It may be that further research will be required before scientists can pin down the precise nature of the planet's natural methane cycle.