Methane (CH4) is a potent greenhouse gas that is roughly 30 times more harmful to the climate than carbon dioxide (CO2). Both gases are produced in thawing permafrost as dead animal and plant remains are decomposed. However, methane is only formed if no oxygen is available. Until now, it was assumed that larger amounts of greenhouse gases are formed when the ground was dry and well aerated—when oxygen was available. Christian Knoblauch and his colleagues have now demonstrated that water-saturated permafrost soils without oxygen can be twice as harmful to the climate as dry soils—which means the role of methane has been greatly underestimated.