Radiation & Climate Oct. 11 • Greenhouse Gases • Aerosols • Clouds • Earth Radiation Budgets QuickTime™ and a TIFF (Uncompressed) decompressor are needed to see this picture. Greenhouse Gases: CO2, and…… CH4, N2O, CFCs Currently, 1/2 of greenhouse effect from CO2, other 1/2 from everything else (CFCs are #2 after CO2) While CO2 conc. has increased, so have the concentrations of other greenhouse gases Methane N2O How can that be ? Radiatively-active Gases, by volume On a per-molecule basis, CFCs have the strongest greenhouse effect And in addition destroy O3, changing stratosphere temperature profile Biologically active ultraviolet radiation reaching The earth’s surface increasing (as strat.ozone decreases) sunburn Plant damage DNA damage UV at TOA TOA UV at Surface with O3 150DU Surface, 150 DU Surface, 300 DU UV at Surface with O3 300DU Greenhouse Gases: can ignore solar Aerosols and Clouds: interact strongly w/ solar Aerosols: range in size from 10-4 to 10 micron Aerosols both scatter and absorb solar and infrared radiation The broad categories: Sulfate (from ocean). Primarily scatters solar, cooling planet Both at surface and at top of atmosphere Black carbon (smoke, soot). Scatters and absorbs solar. Cools Surface but warms at top of atmosphere. Organic carbon Dust Sea salt (large size, thought to encourage precipitation) Aerosols come in 3 Distinct size groups: Nuclei mode Accumulation mode Coarse mode Only the last 2 Become cloud Nuclei; nuclei Mode must first Undergo more chemistry Sulfates arguably the most straightforward SPM 3 Aerosol distribution variable Greenhouse forcing Sulfate forcing Clouds. As a first approximation, infrared emissivity and Cloud albedo can be parameterized as a function of Liquid water path. A further improvement is drop size Note dependence on LWP (and optical depth) becomes unimportant for thick clouds Impact of clouds on climate: Clouds cover ~ 65% of globe. Surface temperature, vertical temperature profile sensitive To cloud amount and cloud height Low clouds cool, high clouds warm planet. This conclusions Rests on optically-thick low clouds, optically-thin high cloud Current interest in high and low cloud trends Global shortwave cloud forcing ~ -45 W m-2 10X that from CO2 doubling ! The ISCCP Project ISCCP trends not necessarily consistent w/ other data Uses of Earth Radiation Budget Data • measure and understand radiation balance driving climate Such as, what do clouds and aerosols do, land use changes • infer energy transports in atmosphere/ocean • radiative parameterizations for energy balance models, such as, regress LW flux, albedo against surface temperature, cloudiness • validate global circulation models QuickTime™ and a TIFF (Uncompressed) decompressor are needed to see this picture. QuickTime™ and a TIFF (Uncompressed) decompressor are needed to see this picture. CERES QuickTime™ and a TIFF (Uncompressed) decompressor are needed to see this picture. Net measured radiation used To estimate energy transport QuickTime™ and a TIFF (Uncompressed) decompressor are needed to see this picture. Next Wedn., Oct. 19, Brian Mapes Will discuss more cloud influences On climate In simple models, Aerosol,cloud scattering Often parameterized By the Henyey-Greenstein Phase function