On the Robustness of Modeled Non-Local Temperature Effects of Historical Land Use Changes

Historically, large areas have been deforested, croplands and rangelands have expanded, and the irrigation area has grown substantially. These land use and land cover changes have altered land surface properties, driving changes in near-surface air temperature. From limited observations and mostly idealized simulations, we know that altering sufficiently large land surface areas can lead to systematic changes in temperature and precipitation outside altered areas. The advection of temperature anomalies, atmosphere, land, and ocean feedbacks are known to be potential drivers of such non-local responses. We show that regionally, non-local temperature signals driven by land-use change can be robustly found in fully coupled Community Earth System Model 2 (CESM2) simulations of the historical period (1850–2014) with all forcings versus all-but-land-use-change forcings. With regional-scale warming of up to more than 1 K and cooling of up to more than 0.5 K, the modeled effects are commensurate to historical temperature effects of all forcings. Regional non-local warming and cooling balance out in the global mean to an effect that is small compared to internal variability (IntV). We analyze how the signal-to-noise ratio of spatially averaged signals depends on the number of ensemble members included from the CESM2 large ensemble. Furthermore, we discuss the ability of our and other signal separation techniques to distinguish different parts of the signal from each other and from IntV. Finally, we discuss future research needs for reliable conclusions on non-local biogeophysical effects of land use change to inform future land-based climate change mitigation strategies.