Changes of climate regimes during the last millennium and the twenty first century as simulated by the Community Earth System Model

Abstract:

This study examined the shifts in terrestrial climate regimes using the Köppen–Trewartha (K–T) climate classification by analyzing the Community Earth System Model Last Millennium Ensemble simulations for 850-2005 (CESM-LME) and the CESM Large Ensemble simulations for 1920-2080 (CESM-LE). We compared K-T climate types of the Medieval Warm Period (950-1250) (MWP) to Little Ice Age (LIA) (1550-1850), present day (1950-2005) (PD) to last millennium (850-1850) (LM), and future (2050-2080) to LM, to place anthropogenic changes in the context of changes due to natural forcings in last millennium. It was shown that the changes in climate types are small between MWP and LIA due to weak changes in temperature and precipitation. The changes in climate types between PD and LM are largely driven by greenhouse gas induced warming but anthropogenic aerosols largely affect the regional climate types by causing a noticeable decrease in precipitation. The impact of natural forcing in LM and anthropogenic aerosols in PD on climate types becomes much smaller than those due to greenhouse gas increase at the end of the 21^st century.