[ATMS 520] Charlson on "The Science Behind Projections of Forced Climate Change: Historical Basis, Open Questions and Implications for Policy Makers"

Start Date/Time: Friday, January 06, 2012, 3:30 PM
Location: JHN 075

Speaker: Robert J. Charlson, Professor of Atmospheric Sciences and Chemistry, UW

Global climate forcing by aerosols (i.e., the change in Earth's energy balance imposed by anthropogenic particles in the atmosphere) is estimated to range from about -0.5 to -1.5 W/m2, which remains as the dominant factor in the uncertainty in total climate forcing (the sum of greenhouse gas plus all other forcings). By comparison, this forcing is opposite in sign and somewhat smaller in magnitude than the current global mean forcing by anthropogenic greenhouse gases of ca. +2.5 W/m2. The uncertainty in total forcing precludes accurate quantification of climate sensitivity from the temperature record over the 20th century; in fact, it has allowed various climate models to fit the T record despite large differences in their climate sensitivity.

This lecture traces the early history of greenhouse gas and aerosol/climate research, in particular the first estimates of aerosol forcing made in the early 1990's, which were largely based on observations of atmospheric aerosol properties. Subsequent efforts have been dominated by models of increasing complexity while attempts at improving the global observational basis via instrumented satellites are underway. Predictably, the total forcing will become less uncertain as the greenhouse gases continue to accumulate in the atmosphere, such that the need for control of those gases will become increasingly urgent, even if the present uncertainty in aerosol forcing is not reduced. Meanwhile, reducing the uncertainty of the aerosol forcing is necessary if we are to be able to understand the causes of the observed warming over the 20th century and to refine the projections of climate change in the future

Coordinator: Prof. Robert Houze (houze@atmos.washington.edu)