Biogeophysical impacts of land use/land cover change on 20th century anthropogenic climate compared to the impacts of greenhouse gas change

The accumulated biogeophysical impact of historical land use/land cover change (LUCC) on the 20th century anthropogenic climate is compared to that of greenhouse gas concentration (GHGC) change by examining four experiments with the Community Earth System Model, including a control run, an LUCC run, a GHGC run and a combined anthropogenic run. Globally, the biogeophysical effect of historical LUCC can offset the warming induced by increased GHG. The overall impacts of LUCC and GHGC tend to be linear in their combination. The linearity of the LUCC and GHGC impacts is stronger on the projected temperature than on the projected precipitation. However, the nonlinearity also shows up in some regions where internal variability is strong. It is also found that the precipitation change scaled to the global mean temperature change induced by LUCC is larger than that induced by GHGC due to more effective changes in water vapour content and atmospheric stability. Regionally, LUCC and GHGC have comparable effects on warming over the mid-latitudes of Asia and the mid-low latitudes of the Americas, whereas the LUCC has a pronounced contribution to cooling over high-latitude regions in the Northern Hemisphere (NH). LUCC and GHGC have the largest impacts on surface temperature over the mid-high latitudes, particularly over the NH, through local and remote processes; in contrast, their impacts on precipitation are primarily over tropical regions through teleconnection processes. Our results propose that more attention should be paid to the interactions between external forcings and internal variabilities, especially over the regions where nonlinearity is strong, such as Europe, North Africa, southern Australia and northwest North America.