Global Climate Change Increases Terrestrial Soil CH4 Emissions

Increased greenhouse gas emissions are causing unprecedented climate change, which is, in turn, altering emissions and removals (referring to the oxidation of atmospheric CH4 by methanotrophs within the soil) of the atmospheric CH4 in terrestrial ecosystems. In the global CH4 budget, wetlands are the dominant natural source and upland soils are the primary biological sink. However, it is unclear whether and how the soil CH4 exchanges across terrestrial ecosystems and the atmosphere will be affected by warming and changes in precipitation patterns. Here, we synthesize 762 observations of in situ soil CH4 flux data based on the chamber method from the past three decades related to temperature and precipitation changes across major terrestrial ecosystems worldwide. Our meta-analysis reveals that warming (average warming of +2 degrees C) promotes upland soil CH4 uptake and wetland soil CH4 emission. Decreased precipitation (ranging from -100% to -7% of local mean annual precipitation) stimulates upland soil CH4 uptake. Increased precipitation (ranging from +4% to +94% of local mean annual precipitation) accelerates the upland soil CH4 emission. By 2100, under the shared socioeconomic pathway with a high radiative forcing level (SSP585), CH4 emissions from global terrestrial ecosystems will increase by 22.8 +/- 3.6 Tg CH4 yr(-1) as an additional CH4 source, which may be mainly attributed to the increase in precipitation over 30 degrees N latitudes. Our meta-analysis strongly suggests that future climate change would weaken the natural buffering ability of terrestrial ecosystems on CH4 fluxes and thus contributes to a positive feedback spiral. Plain Language Summary This study is the first investigation to include scenarios of CH4 sink-source transition due to climate change and provides the global estimate of soil CH4 budgets in natural terrestrial ecosystems in the context of climate change. The enhanced effect of climate change on CH4 emissions was mainly attributed to increased CH4 emissions from natural upland ecosystems. Although an increased CH4 uptake by forest and grassland soils caused by increased temperature and decreased precipitation can offset some part of additional CH4 sources, the substantial increase of increased precipitation on CH4 emissions makes these sinks insignificant. These findings highlight that future climate change would weaken the natural buffering ability of terrestrial ecosystems on CH4 emissions and thus form a positive feedback spiral between methane emissions and climate change.