Understanding the Rapid Precipitation Response to CO₂ and Aerosol Forcing on a Regional Scale

• Published in: Journal of climate 2016-01, Vol.29 (2), p.583-594
• Main Authors: Richardson, Thomas B., Forster, Piers M., Andrews, Timothy, Parker, Doug J.
• Format: Article
• Language: English
• Subjects: Aerosols; Anthropogenic factors; Carbon dioxide; Climate change; Climate models; Convection; Cooling; Diabatic cooling; Energy; Energy budget; Experiments; Heat; Land surface temperature; Long-term changes; Normal distribution; Oceans; Pattern analysis; Precipitation; Radiation; Sea surface; Sea surface temperature; Simulation; Sulfates; Surface temperature; Temperature changes; Tropical environments; Troposphere
• ISSN: 0894-8755; 1520-0442
• DOI: 10.1175/jcli-d-15-0174.1

Precipitation exhibits a significant rapid adjustment in response to forcing, which is important for understanding long-termclimate change. In this study, fixed sea surface temperature (SST) simulations are used to analyze the spatial pattern of the rapid precipitation response. Three different forcing scenarios are investigated using data obtained from phase 5 of CMIP (CMIP5): an abrupt quadrupling of CO₂, an abrupt increase in sulfate, and an abrupt increase in all anthropogenic aerosol levels from preindustrial to present day. Analysis of the local energy budget is used to understand the mechanisms that drive the observed changes. It is found that the spatial pattern of the rapid precipitation response to forcing is primarily driven by rapid land surface temperature change, rather than the change in tropospheric diabatic cooling. As a result, the pattern of response due to increased CO₂ opposes that due to sulfate and all anthropogenic aerosols, because of the opposing surface forcing. The rapid regional precipitation response to increased CO₂ is robust among models, implying that the uncertainty in long-term changes is mainly associated with the response to SST-mediated feedbacks. Increased CO₂ causes rapidwarming of the land surface,which destabilizes the troposphere, enhancing convection and precipitation over land in the tropics. Precipitation is reduced over most tropical oceans because of a weakening of overturning circulation and a general shift of convection to over land. Over most land regions in the midlatitudes, circulation changes are small. Reduced tropospheric cooling therefore leads to drying over many midlatitude land regions.