Future Global Soil Respiration Rates Will Swell Despite Regional Decreases in Temperature Sensitivity Caused by Rising Temperature

Between 1960 and 2014, the global soil respiration (RSG) 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 (RS) to temperature may alter the overall increase in rates of RS because the RS rates of some regions may decelerate while others continue to rise. Using monthly global RS data, we modeled the relationship between RS and temperature for the globe and eight climate regions and estimated RSG between 1961 and 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 RSG increase (0.05 Pg C year⁻¹) was similar to the RSG increase of previous estimates. However, under the RCP8.5 scenario, which estimates approximately 3 °C of warming globally, the forecasted acceleration of RSG increased to an average of 0.12 Pg C year⁻¹. Under RCP8.5, the temperature sensitivity of RS declined in the arid, winter-dry temperate, and tropic. These regional declines were offset by increased RS sensitivity and fluxes from the boreal and polar regions. In contrast, under RCP2.6 RSG decelerated slightly from current rates. If rising greenhouse gas emission remains unmitigated, future increases in RSG 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.