Abstract
Wetland methane (CH(4)) emissions are the largest natural source in the global CH(4) budget, contributing to roughly one third of total natural and anthropogenic emissions. As the second most important anthropogenic greenhouse gas in the atmosphere after CO(2), CH(4) is strongly associated with climate feedbacks. However, due to the paucity of data, wetland CH(4) feedbacks were not fully assessed in the Intergovernmental Panel on Climate Change Fifth Assessment Report. The degree to which future expansion of wetlands and CH(4) emissions will evolve and consequently drive climate feedbacks is thus a question of major concern. Here we present an ensemble estimate of wetland CH(4) emissions driven by 38 general circulation models for the 21st century. We find that climate change-induced increases in boreal wetland extent and temperature-driven increases in tropical CH(4) emissions will dominate anthropogenic CH(4) emissions by 38 to 56% toward the end of the 21st century under the Representative Concentration Pathway (RCP2.6). Depending on scenarios, wetland CH(4) feedbacks translate to an increase in additional global mean radiative forcing of 0.04 W·m(-2) to 0.19 W·m(-2) by the end of the 21st century. Under the "worst-case" RCP8.5 scenario, with no climate mitigation, boreal CH(4) emissions are enhanced by 18.05 Tg to 41.69 Tg, due to thawing of inundated areas during the cold season (December to May) and rising temperature, while tropical CH(4) emissions accelerate with a total increment of 48.36 Tg to 87.37 Tg by 2099. Our results suggest that climate mitigation policies must consider mitigation of wetland CH(4) feedbacks to maintain average global warming below 2 °C.