AAAR 35th Annual Conference October 17 - October 21, 2016 Oregon Convention Center Portland, Oregon, USA
Abstract View
Aerosol, Cloud, and Precipitation Responses to Northern Hemisphere Aerosol Emissions Reductions in Three Climate Models
DANIEL WESTERVELT, Arlene Fiore, Gustavo Correa, Andrew Conley, Jean-François Lamarque, Drew Shindell, Columbia University Lamont-Doherty Earth Observatory
Abstract Number: 487 Working Group: Aerosols, Clouds, and Climate
Abstract It is widely expected that global and regional emissions of atmospheric aerosols and their precursors will decrease strongly throughout the remainder of the 21st century, due to emission reduction policies enacted to protect human health. Reductions in emissions of black carbon aerosols (and other short-lived climate pollutants) have been discussed recently as a potential option for near-term climate mitigation. Although there is some evidence that regional climate effects of aerosols can be significant, we currently lack a full understanding of the magnitude, spatial and temporal pattern, and statistical significance of these influences, especially in clouds and precipitation. Further, we often lack robust understanding of the processes responsible for these influences of regional aerosols on local and remote climate. Here, we aim to quantify systematically the cloud and precipitation response to regional changes in aerosols through model simulations using three fully coupled chemistry-climate models: NOAA Geophysical Fluid Dynamics Laboratory Coupled Model 3 (GFDL CM3), NCAR Community Earth System Model (CESM), and NASA Goddard Institute for Space Studies ModelE2 (GISS-E2). The central approach we use is to contrast a long control experiment (400 years) with a collection of long individual perturbation experiments (~200 years). We perturb emissions of sulfur dioxide (precursor to sulfate aerosol) and carbonaceous aerosol (BC and OM) within several world regions and asses which responses are significant relative to internal variability and robust across the three models. Initial results show consistent decreases in cloud droplet number, cloud effective radius, and liquid water path across the three models due to decreases in aerosols. Aerosols impact tropical precipitation strongly in each of the models, although there is less commonality among the three modeled responses. Despite prior work indicating a robust northward ITCZ shift in response to reduced future aerosol forcing, we find that only one of the models simulates a clear northward shift in the ITCZ due to the warming induced by U.S, European, or Chinese aerosol reductions. Our approach enables us to develop a basis for understanding the regional and global climate changes to regional aerosols.