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12. Climate Ch 3aMech

12. Climate Ch 3aMech - What regulates global temperature H...

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1 What regulates global temperature? Heat Balance: Energy in = Energy out Energy in = (Solar output)( π r 2 )(1-A)/(4 π R 2 ) Energy out = (4 π r 2 ) σ T 4 r = Earth radius R = Earth sun dist. A = Albedo T = °K Global Temperature Depends on: Radiation balance predicts Black Body Temperature: Energy in = Energy out σ T 4 = (Solar output)(1-A)/(16 π R 2 ) For A = 0.30, T = 255 °K = -18°C Critical Factors: 1. Solar output - increases over long term. Short term variation? 2. Earth-sun distance (R) - average is constant, orbit shape changes. 3. Albedo (A) - ice cover, dust, cloud cover can change 4. Greenhouse factor - can change with H2O, CO2 content. 5. Efficiency of heat transport to poles dictates uniformity of T - can vary with mountains, continent position, location of deep water production. 748 Grand Canyon: Why the great unconformity? Snowball Earth Late Proterozoic had glaciation to low latitudes. Continents and perhaps oceans were mostly ice covered ->high albedo!!! (runaway albedo) How can Earth escape? CO2 should provide negative feedback. Why? CO2 is added from volcanism related to subduction.
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