Isolating the Evolving Contributions of Anthropogenic Aerosols and Greenhouse Gases: A New CESM1 Large Ensemble Community Resource

• DOI: 10.1175/jcli-d-20-0123.1
• Publication Date: 2020-08-12T00:20:07Z
• Authors: Clara Deser; Adam S. Phillips; Isla R. Simpson; Nan Rosenbloom; Dani Coleman; Flavio Lehner; Angeline G. Pende...; Pedro DiNezio; Samantha Stevenson
• Keywords: Forcing (mathematics)

Abstract The evolving roles of anthropogenic aerosols (AER) and greenhouse gases (GHG) in driving large-scale patterns precipitation SST trends during 1920–2080 are studied using a new set “all-but-one-forcing” initial-condition large ensembles (LEs) with the Community Earth System Model version 1 (CESM1), which complement original “all-forcing” CESM1 LE (ALL). number ensemble members (15–20) each LEs enables regional impacts AER GHG to be isolated from noise model’s internal variability. Our analysis approach, based on running 50-yr trends, accommodates geographical temporal changes forcing response. shown primary driver externally forced ALL before late 1970s, dominate thereafter. spatially distinct except 1970s transition phase when aerosol mainly confined lower latitudes. is also characterized by relative minimum amplitude trend ALL, due combination reduced partially offsetting effects GHG. Internal variability greatly limits detectability AER- GHG-forced individual realizations pattern correlation metrics, especially historical period, highlighting need for LEs. We estimate that <20% spatial variances observed attributable forcing, although model biases response signal-to-noise may affect this estimate.