Combining temperature and precipitation to constrain the aerosol contribution to observed climate change

Abstract

Abstract Using the past to improve future predictions requires an understanding and quantification of the individual climate contributions to the observed climate change by aerosols and greenhouse gases (GHG), which is hindered by large uncertainties in aerosol forcings and responses across climate models. To estimate historical aerosol responses, we apply detection and attribution methods to attribute a joint change in temperature and precipitation to forcings by combining signals of observed changes in tropical wet and dry regions, the interhemispheric temperature asymmetry, global mean temperature (GMT) and global mean land precipitation (GMLP). Fingerprints representing the climate response to aerosols (AER) and the remaining external forcings (noAER; mostly GHG) are derived from large-ensembles of historical single- and ALL-forcing simulations from three models in phase 6 of the Coupled Model Intercomparison Project and selected using a perfect model study. Results from an imperfect model study and a hydrological sensitivity analysis support combining our choice of temperature and precipitation fingerprints into a joint study. We find that diagnostics including temperature and precipitation slightly better constrain the noAER signal than diagnostics based purely on temperature or GMT-only and allow for the attribution of AER cooling (even when GMT is not included in the fingerprint). These results are robust across, using fingerprints from different climate models. Estimated contributions for AER and noAER agree with estimates from the most recent IPCC report. Finally, we attribute a best estimate of 0.46 K (0.05–0.86 K) of aerosol-induced cooling and of 1.63 K (1.26–2.00 K) of noAER warming in 2010–2019 relative to 1850–1900 using the combined signals of GMT and GMLP.