UMD AOSC Seminar
The Impact of Tropospheric Aerosols, Volcanoes, and Ocean Circulation on Global Climate
Professor Ross Salawitch and Dr. Tim Canty
University of Maryland
We examine the globally averaged surface temperature record, from 1900 to present, in terms of historical change in external factors that drive the radiative forcing of climate. The most uncertain external factor is net anthropogenic aerosol radiative forcing (NAARF). We present a new, simple parameterization for NAARF tied to emission time series for 6 types of aerosols (4 that cool, 2 that warm) provided in a database prepared for the next IPCC report. We use this parameterization to assess the impact of uncertainty in NAARF on our understanding of past and future climate. Our model can be tuned to match the observed temperature record via use of either substantial internal climate feedbacks to offset large NAARF cooling or moderate climate feedback together with slight NAARF cooling: clearly, this type of cantilevering is operative within IPCC climate models. We show that remarkably close consistency between modeled and measured surface temperature anomalies can be achieved, independent of NAARF, when temporal variation in the exchange of heat between the atmosphere and oceans is considered. We suggest increases in stratospheric aerosol optical depth following the eruption of Mt. Pinatubo and other volcanoes during the past century have had a much smaller influence on global climate than is commonly assumed. Model tuning, while perhaps benign for our understanding of past climate, has considerable consequences for projections of future climate. We suggest uncertainties in the projection of future climate could be greatly reduced if the community could precisely define NAARF for the present-day climate system.
Note: this presentation reports on work carried out at UMCP by Tim Canty, Nora Mascioli, Matthew Smarte, and Ross Salawitch.
Thursday, March 15, 2012
AOSC494: Atmospheric and Oceanic Science Seminar
AOSC 818: Frontiers in Atmosphere, Ocean, Climate, and Synoptic Meteorology Research