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Between 1960 and 2014, the global soil respiration (R-SG) flux increased at a rate of 0.05 Pg C year(-1) however, future increase is uncertain due to variations in projected temperature and regional heterogeneity. Regional differences in the sensitivity of soil respiration (R-S) to temperature may alter the overall increase in rates of R-S because the R-S rates of some regions may decelerate while others continue to rise. Using monthly global R-S data, we modeled the relationship between R-S and temperature for the globe and eight climate regions and estimated R-SG between 1961and 2100 using historical (1961-2014) and future (2015-2100) temperature data [Representative Concentration Pathways (RCP2.6 and RCP8.5)]. Importantly, our approach allowed for estimation of regional sensitivity, where respiration rates may peak or decline as temperature rises. Estimated historical R-SG increase (0.05 Pg C year(-1)) was similar to the R-SG increase of previous estimates. However, under the RCP8.5 scenario, which estimates approximately 3 degrees C of warming globally, the forecasted acceleration of R-SG increased to an average of 0.12 Pg C year 1 . Under RCP8.5, the temperature sensitivity of R(S )declined in the arid, winter-dry temperate, and tropic. These regional declines were offset by increased R(S)( )sensitivity and fluxes from the boreal and polar regions. In contrast, under RCP2.6 R-SG decelerated slightly from current rates. If rising greenhouse gas emission remains unmitigated, future increases in R-SG will be much faster than current and historical rates, thereby possibly enhancing future losses of soil carbon and contributing to positive feedback loops of climate change.

Plain Language summary Between 1960 and 2014, the global CO2 flux increased at a rate of 0.05 Pg carbon per year; however, future increase of CO2 emission from soil is uncertain. Regional differences in the sensitivity of soil CO2 efflux to temperature change may alter the overall soil CO2 emission. We modeled the relationship between soil CO2 efflux and temperature for the globe and eight climate regions, and estimated global soil CO2 efflux between 1961and 2100 using historical temperature data (1961-2014) and future temperature (2015-2100, RCP 2.6 and 8.5). Estimated historical global soil CO2 efflux acceleration (0.05 Pg carbon per year) was similar to the global soil CO2 efflux acceleration of previous estimates. However, under the RCP8.5, which estimates approximately 3 degrees C of warming globally, the forecasted acceleration of global soil CO2 efflux increased to 0.12 Pg carbon per year. In contrast, under the RCP 2.6 scenario, the global soil CO2 efflux rate decelerated slightly from current rates. If rising greenhouse gas emission remains unmitigated, future acceleration of global soil CO2 efflux will be much faster than current and historical rates, thereby enhancing future losses of soil carbon and contributing to accelerate climate change.