Methane Emissions on the Rise

Industrial greenhouse-gas increase has been masked by natural declines.

Current projections of methane emissions are likely to be too optimistic, an international team of atmospheric scientists reports today in Nature.

Methane, which is less abundant in the atmosphere than carbon dioxide but 20 times more potent as a greenhouse gas, is thought to have been responsible for up to one-third of global warming since the industrial revolution.

Unlike CO₂, however, atmospheric methane concentrations stopped rising in the 1990s, probably as a result of the sharp decline of the Soviet Union's industrial power. Concentrations have remained relatively stable since 1999, giving the impression that human and natural methane sources and sinks may have reached a lasting balance.

But the most extensive study so far suggests this is not so: human-created sources are rising, but have been masked by natural declines.