Anthropogenic influence on extreme temperatures in China based on CMIP6 models

With rapid warming since the mid-20th century, China has experienced remarkable changes in the extreme temperatures. We use the updated observational data and the newest generation of climate models from Coupled Model Intercomparison Project Phase 6 (CMIP6) to investigate the relative contribution from different external forcing to the temperature extremes. We find that both intensity and frequency indices of extreme temperature experience continuous warming during 1951-2018. More intense and more frequent warm extremes and less intense and less frequent cold extremes are observed in most regions. An exception is a warming slowdown in the intensity of the coldest extremes since the late 1990s in northeast China. These observed changes are generally well reproduced by CMIP6 climate models, especially for the warm days and nights. Detection analyses based on an optimal fingerprinting method show that anthropogenic forcing (ANT) is the main driver for these changes, with cold extremes less detectability than warm extremes. Three-signal detections show that both greenhouse gas (GHG) and anthropogenic aerosols (AA) influences can be detected and separated in most warm extreme indices but not in the cold extremes, while the natural forcing influence is negligible for most indices. GHG forcing plays a dominant role, accounting for about 1.6 (1.1-2) times of observed warming in changes of most indices, while the AA offset about 35% (10-60%) of GHG induced warming for warm extremes. Anthropogenic factors including land use and ozone may have a very small positive contribution to the extreme temperatures.