Скачать или смотреть Seminar: Dan Westervelt, 2015-01-14

GISS Lunch Seminar: Jan. 14, 2105
Dan Westervelt (Princeton)
The impact of projected decreasing aerosol concentrations on future climate

Presentation slides available at http://www.giss.nasa.gov/meetings/lun...

It is widely expected that global emissions of atmospheric aerosols and their precursors will decrease strongly throughout the remainder of the 21st century, due to emission reduction policies enacted based on human health concerns. However, the resulting decrease in atmospheric aerosol burden will have unintended climate consequences. Since aerosols generally exert a net cooling influence on the climate, their removal will lead to an unmasking of global warming from long-lived greenhouse gases as well as other changes to the climate system. Global emissions of aerosols and their precursors are projected to decrease by as much as 80% by the year 2100, according to the four Representative Concentration Pathway (RCP) scenarios. We use the Geophysical Fluid Dynamics Laboratory Climate Model version 3 (GFDL CM3) to simulate future climate over the 21st century with and without aerosol emission changes projected by the RCPs in order to isolate the radiative forcing and climate response resulting from the aerosol reductions. We find that up to 1 W m-2 of radiative forcing may be unmasked globally by 2100 due to reductions in aerosol and precursor emissions, leading to average global temperature increases up to 1 K and global precipitation rate increases up to 0.09 mm d-1 (3% of 2005 values). Global and regional changes in two climate parameters related to the aerosol indirect effectÑliquid water path (LWP) and cloud droplet effective radius are also assessed and also closely follow the projected RCP emissions and energy consumption trends over the 21st century. Global cloud droplet effective radius is projected to increase by up to 0.6 micron (5%) and global LWP is projected to decrease by up to 1.0 g m-2 (2%). Regionally and locally, climate impacts are much larger, as RCP8.5 projects a 2.1 K warming over China, Japan, and Korea due to reduced aerosol emissions, as well as nearly a 0.2 mm d-1 precipitation increase, a 7 g m-2 LWP decrease, and a 2 micron increase in cloud droplet effective radius. We find that the projected future aerosol optical depth, radiative forcing, and climate response global trends do not vary significantly across the four different RCPs, highlighting the need for development of future scenarios that encompass a broader range of emissions trajectories for aerosols and their precursors. The expected unmasking of additional global warming from aerosol reductions may require more aggressive greenhouse gas mitigation policies than anticipated in order to reach a desired climate target.