9/29/20101Greenhouse effect and global warmingThe Greenhouse Effect and The Greenhouse Effect and Atmospheric WarmingAtmospheric Warming• Why is it called greenhouse effect?• What is the difference between the greenhouse effect and real greenhouses?9/29/20102• Greenhouse gases make up about 1% of the earth atmosphere• Without the greenhouse gases, the earth’s average temperature would be close to -18°CThe Greenhouse Effect and The Greenhouse Effect and Atmospheric WarmingAtmospheric Warming9/29/20103Most important greenhouse gasesGas Formula Contribution (%)Water Vapor H2O 36 – 72 % Carbon Dioxide CO29 – 26 %Methane CH44 – 9 % Ozone O33 – 7 % Do these numbers imply that CO2 is responsible for 9-26% of the earth warming?Greenhouse gases• Water vapor is the most dominant greenhouse gas. • Water vapor is the dominant positive feedback in the climate system and amplifies warming caused by changes in atmospheric CO2. • This positive feedback is why climate is so sensitive to CO2 warming.9/29/20104Main non-gas contributors to the greenhouse effect: CloudsHow does the altitude of the clouds influence the greenhouse effect?• Actually clouds do both– 1)act as insulation warming the earth– 2)reflect insolation cooling the earthClouds and Greenhouse effect9/29/20105COCO22 and warmingand warming• Why does CO2receive so much attention in the climate warming context?• Carbon dioxide accounts for a significant fraction of the enhanced greenhouse effect.• The level of carbon dioxide in the atmosphere is increasing by more than 10% every 20 yrs due to human activity.COCO22 and warmingand warming9/29/20106COCO22 and warmingand warming• Natural sources of atmospheric CO2– volcanic outgassing– combustion of organic matter – respiration of aerobic organismsCOCO22 and warmingand warmingAnthropogenic sources?9/29/20107Source epa.govSource epa.gov9/29/20108COCO22 and warmingand warming• Natural land and ocean CO2sinks removed 57% of all CO2emitted from human activities during the 1958-2008• Atmospheric lifetime of CO2is 50 to 200 yrs.• Global warming will continue to affect the Earth for hundreds of years.What about CHWhat about CH44and warming?and warming?• Methane is 25 times more potent as a greenhouse gas than CO2(but it’s at lower concentrations in the atmosphere)9/29/20109What about CHWhat about CH44and warming?and warming?• Largest anthropogenic sources of methane emissions (for USA only):– decomposition of wastes in landfills– ruminant digestion– manure management associated with livestock– natural gas and oil systemsWhat about CHWhat about CH44and warming?and warming?• There is some uncertainty about the potential future contributions of CH4to global warming.• Positive feedbacks triggered by elevated temperatures could release large amounts of CH4to the atmosphere.9/29/201010• Let’s now see some of the