Effects of human activities and natural forcings on multiscale changes of global land surface air temperature simulated by CMIP6 Models

Quantifying the quantitative contribution of human activities to climate change is a core scientific issue in climate change detection and attribution studies, and it is also an important scientific basis for improving the level of climate change prediction and estimation. Using the Detection and Attribution Model Intercomparison Project (DAMIP) from the sixth phase of the Coupled Model Intercomparison Project (CMIP6), we focused on detecting the influence of anthropogenic forcing (ANT) and natural external forcing (NAT) on the multi-scale changes of global surface temperature in the last 100 years (1915-2014). The relative contributions of different anthropogenic factors such as greenhouse gases (GHG), anthropogenic aerosols (AA), and land use (LU) and the differences between the northern and southern hemispheres were also attributed and analyzed. The results show that the significant impacts of GHG and AA emissions began to be detected in most regions of the world between 1965 and 1980, and that the cooling effect of AA in the Northern Hemisphere was ahead of the warming effect of GHG. Human-induced actual global land warming in the last 100 years is about 1.1 degrees C (0.80 degrees C similar to 1.3 degrees C), with a contribution of about 1.2 degrees C to the Northern Hemisphere and about 0.7 degrees C in the Southern Hemisphere. Although internal variability is the main factor for most regional temperature decadal (10-30 years) and multi decadal (30-60 years) variations, the variance contribution of anthropogenic and natural forcing in the global interdecadal variability of surface air temperature is about 5%similar to 20%. However, the variance contribution of both in the northern hemisphere, especially in the mid and high latitudes of East Asia and Europe, can reach 50% in the multidecadal variability of surface air temperature. Anthropogenic forcing can increase the risk of extreme heat events by about 3 times,with a higher risk in the northern hemisphere than in the southern hemisphere.