1GS106 Overview of Greenhouse EffectI. IntroductionA. Infrared Active Gases ("Greenhouse Gases")1. Water Vapor2. Carbon Dioxide3. OzoneB. Greenhouse Process1. Absorb Thermal Infrared Radiation (heat) reflected by Earth's surface andatmosphere2. Atmospheric warming, warming of Earth surface, warming of lower troposphere3. Net Result: average Earth surface temperature = 30 C higher than it would beowithout the Greenhouse processC. Historic Consideration1. rapid increase in concentration of Greenhouse gases since the industrial period(1800's)II. Greenhouse Gases and Earth-Atmosphere Energy BalanceA. Historic Greenhouse Gas Concentrations1. Carbon Dioxide (CO )2a. concentrations(1) pre-industrialconcentration = 280ppm(2) post-industrialconcentration (1997) =364 ppmb. Source: burning of fossil fuels(1) Carbon Loading: 6.5 x10 g carbon / year15(2) loading exceeds uptakeof carbon dioxide byatmosphere and oceans(a) net result: >carbon dioxideconcentrations2c. Carbon Dioxide Sinks (removal processes)(1) oceanic dissolution(2) burial in soils / deep sea sediments (calcium carbonate deposits)d. Residence Times for Anthropogenic Input:(1) decades to centuries, with 15-30% remaining for thousands ofyears2. Methane (CH )4a. concentrations(1) pre-industrial = 700 ppb(2) post-industrial (1994) = 1721 ppbb. Source(1) fossil fuels(a) 70 - 120 x 10 g CH / yr124(2) Agriculture, Landfills(a) 200 - 350 x 10 g CH / yr124c. Estimated residence time for anthropogenic input: 10 years in atmosphere3. Nitrogen Oxide (N O)2a. concentrations(1) preindustrial = 275 ppb(2) post-industrial (1994) = 312 ppbb. Source: agriculture and industry(1) 3-8 x 10 g N / yr12B. Greenhouse Processes1. anthropogenic greenhouse gas increases atmospheric absorption of InfraredRadiationa. result: (1) warming of troposphere and Earth surface(2) cooling influence on stratosphereb. Carbon Dioxide: most long-lived greenhouse gas in atmosphere, mostimportant factor2. Complex Feedback and Responsea. global warming, induces increased evaporation, increases water vapor,increases cloud cover, increases albedo, promotes coolingb. local vs. global responsec. feedback systems uncertain, complex interaction of variables3III. Climate Change and Carbon Dioxide ContentA. Surface Air Temperature1. historic global temperature monitoringa. results: increase of 0.3 to 0.6 degree C over past 150 yearsb. temperature increase is variable, this is a long term average trendB. Climate / Temperature Proxy Data1. tree ring records2. ice sheets / ice caps / Glaciersa. present on every continent except Australiab. geographically distributed / regional climate indicatorsc. NOTE: glaciers have been notably receeding for the past century(globally)3. Ice Records over past several centuries (pre-industrial greenhouse gas influx)a. show variations in global warming and cooling w/o anthropogenicinfluenceb. RESULT: many variables influence climate, not just greenhouse gasesc. Carbon Dioxide Records (ice bubbles)(1) natural variation in atmospheric CO2 = 80 - 100 ppm +/-(2) glacial climate correlates to low CO2(3) interglacial climate correlates to high CO2C. Disussion1. paleoclimate data suggests there isnatural variation of greenhousegases, outside the influence ofanthropogenic activity2. there is definitely a link betweencarbon dioxide content andatmospheric heating / cooling3. many variables exist in a complexsystem4. historically: there is definitely adramatic increase in CO2 levels inatmosphereIV. Global Response to Climate Change and Greenhouse EffectA. Anticipated Effects - Results of Modeling Studies1. increase in mean air temperaturea. doubling CO2 content === increase of 2 deg. C2. increase in levels of evaporation and precipitationa. increased heat in atmosphereb. increased evaporationc. increased rainfall / storm intensityd. increased flooding3. melting of ice sheetsa. e.g. Greenland Ice Sheet: thinning of ice sheet in past decade by up to 1m/yr at lower elevations44. rising sea levela. tide records for past century(1) mean sea level rise of ~ 18 cm /100 yrsb. thermal expansionc. volume increase5. changes in biosphere / ecosystemsa. increase in active growing season at high latitudesV. Summary PointsA. Anthropogenic greenhouse gaseshave increased significantly duringthe industrial periodB. Effects of greenhouse gasesexpected to exist for up to 1000's ofyearsC. Increased greenhouse gases cause >infrared absorption, and heating ofatmosphereD. Global mean air temp. have > 0.3 -0.6 C in past 150 yearsE. Over the past thousands of years,climate has changed with littlechange in CO2 contentF. Anticipated changes in system due toglobal warming include: 1. increased air temperature2. increased precipitation andevaporation3. rising sea level4. changes in
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