Cross continental increase in methane ebullition under climate change.

Methane (CH ₄ ) strongly contributes to observed global warming. As natural CH ₄ emissions mainly originate from wet ecosystems, it is important to unravel how climate change may affect these emissions. This is especially true for ebullition (bubble flux from sediments), a pathway that has long been underestimated but generally dominates emissions. Here we show a remarkably strong relationship between CH ₄ ebullition and temperature across a wide range of freshwater ecosystems on different continents using multi-seasonal CH ₄ ebullition data from the literature. As these temperature-ebullition relationships may have been affected by seasonal variation in organic matter availability, we also conducted a controlled year-round mesocosm experiment. Here 4 °C warming led to 51% higher total annual CH ₄ ebullition, while diffusion was not affected. Our combined findings suggest that global warming will strongly enhance freshwater CH ₄ emissions through a disproportional increase in ebullition (6-20% per 1 °C increase), contributing to global warming.