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Response of the surface climate to anthropogenic forcing in two coupled models

Presentation Date
Monday, December 11, 2023 at 8:30am - Monday, December 11, 2023 at 12:50pm
MC - Poster Hall A-C - South



Multiple lines of observed evidence show an increase in global mean surface temperature in the last 150 years. Large-ensemble model simulations has been used to access the response of the climate system to different external forcings and the influence of the external forcings on the internal variability. To remove the influence of the external forcing, it is a common practice to use the single model large-ensemble mean or the multi-model ensemble mean to represent the external forcing induced changes. Here, by analyzing two large-ensembles from the Community Earth System Model version 2 (CESM2) and the Energy Exascale Earth System Model version 2 (E3SMv2), we explore how well the large ensemble mean can represent the response of the climate system to the external forcing using the empirical orthogonal Function analysis (EOF). We found that the greenhouse gas effect and the volcanic aerosols appear in EOF1 in CESM2, but EOF2 in E3SMv2, the anthropogenic aerosol effects are in EOF2 for CESM2, but EOF1 for E3SMv2. However, EOF3 in both model ensembles show an interdecadal Pacific variability (IPO) like pattern, which could be evidence suggesting the influence of the external forcing on the internally generated IPO. Further analysis on the surface temperature shows that due to a much weaker mean state of the Atlantic Meridional Overturning circulation (AMOC) in E3SMv2 preindustrial control run relative to that in CESM2, the warming in the Northern Hemisphere is generally less in E3SMv2 than in CESM2 during the historical period, but more in SSP370 period (especially in the subpolar North Atlantic region). This is an indication that the mean state of AMOC can affect the response of the regional and global climate to the external forcing changes by altering the oceanic stratification.

Funding Program Area(s)