HR: 15:25h
AN: A32C-07    [PDF]
TI: Modeling Radiative Forcing by Aerosols: How Good is Good Enough?
AU: * Schwartz, S E
EM: ses@bnl.gov
AF: Atmospheric Sciences Division, Brookhaven National Laboratory, Bldg 815E, Upton, NY 11973 United States
AB: Radiative forcing of climate change by anthropogenic aerosols is now recognized as the largest uncertainty in climate forcing {\it F} over the industrial period. This uncertainty limits inference of Earth's climate sensitivity $\lambda$ either empirically or by comparison of observed temperature change over the industrial period $\Delta${\it T} with modeled temperature change obtained by imposing a time-dependent forcing in a climate model. Either way, for a desired uncertainty in $\lambda$ of, say, 30% (e.g., temperature increase resulting from doubling atmospheric CO$_{2}$ $\Delta${\it T}$_{2x}$ = 3 $\pm$ 1 K), the required uncertainty in {\it F} is about 20%. The resultant required uncertainty in aerosol forcing depends on the magnitude of this for cing. If total aerosol forcing is small, the requisite uncertainty can be quite large, e.g., a factor of 2 for aerosol forcing -0.4 W m$^{-2}$. However as aerosol forcing magnitude increases the requirement is much more stringent, e.g., for aerosol for c ing -1.2 W m$^{-2}$, 10%, comparable to present uncertainty in greenhouse gas forcing. This talk examines quantifiable uncertainties in aerosol forcing and apportions them between contributions from atmospheric chemistry, atmospheric radiation, and c l ou d microphysics. Unless and until present uncertainties are greatly reduced it will not be possible to place confident limits on Earth's climate sensitivity, limiting society's ability to confidently plan to adapt to or mitigate future climate chang e arising from increasing atmospheric concentrations of greenhouse gases. n
UR: http://www.ecd.bnl.gov/steve/schwartz.html
DE: 0305 Aerosols and particles (0345, 4801)
DE: 0320 Cloud physics and chemistry
DE: 0360 Transmission and scattering of radiation
DE: 0365 Troposphere--composition and chemistry
DE: 1610 Atmosphere (0315, 0325)
SC: Atmospheric Sciences [A]
MN: 2003 Fall Meeting