1. The Greenhouse Effect A quick review

2. The Greenhouse Effect A natural process that keeps the surface of the earth at a habitable temperature. A natural process that keeps the surface of the earth at a habitable temperature. –Without the greenhouse effect, surface temperatures would be about 60º F colder. –There would be NO liquid water!

3. How does it work? Image source: kids.earth.NASA.gov

4. How does it work? Short wavelength (ultraviolet) radiation from Sun reaches Earth Short wavelength (ultraviolet) radiation from Sun reaches Earth Earth warms and emits long wavelength (infrared) radiation back towards space Earth warms and emits long wavelength (infrared) radiation back towards space Greenhouse gases in Earth’s atmosphere “trap” some of the infrared radiation near Earth Greenhouse gases in Earth’s atmosphere “trap” some of the infrared radiation near Earth –Think of your car on a sunny day: the sunlight enters through the closed windows and warms the car interior. That heat can’t escape back out through the glass.

5. What are the main Greenhouse Gases? Water vapor (H 2 O) Carbon dioxide (CO 2 ) Methane (CH 4 ) Nitrous oxide (N 2 O) These were all present in atmosphere before humans, but we are adding more

6. Greenhouse Gases allow ~75% of short wavelength energy from Sun to reach Earth. Only 15-30% of the energy re-radiated by Earth escapes back through greenhouse gases in the atmosphere. Image created by Robert A. Rohde / Global Warming Art http://www.globalwarmingart.com/wiki/File:Atmospheric_Transmission_png

7. Greenhouse Gas Efficiency Gas Relative greenhouse efficiency per molecule Concentration in the atmosphere (ppm) Relative efficiency x concentration (ppm) Carbon Dioxide (CO 2 ) 1350350 Methane (CH 4 ) 301.751 Nitrous Oxide (N 2 O) 1600.3149.6 Ozone (O 3 ) 20000.06120 Chlorofluoro carbons (CFCs) 21,0000.000265.46

8. Anthropogenic Greenhouse Gas Sources Water (H 2 O) –sources largely natural, but large amounts added during rocket launches Carbon Dioxide (CO 2) –Burning fossil fuels (cars, factories, power plants, etc.) –Burning forests (landuse conversion) –Rocket launches

9. Anthropogenic Greenhouse Gas Sources Methane (CH 4 ) –Enteric fermentation (cow burps!) –Landfill emissions –Rice cultivation –Natural gas use –Melting of permafrost in Arctic Nitrous Oxide (N 2 O) –Agricultural processes (fertilizers) Buuurp!

10. Anthropogenic Greenhouse Gas Sources What about CFCs? Very powerful greenhouse gas, but people have been very successful at reducing emissions (Montreal Protocol)

11. Effect on Upper Atmosphere The Greenhouse Effect causes warming at Earth’s surface, but cooling in upper atmosphere The Greenhouse Effect causes warming at Earth’s surface, but cooling in upper atmosphere –If more of Earth’s emitted longwave radiation is held close to the surface, it is not available to cause warming in the upper atmosphere –More noctilucent cloud formation in the Mesosphere? (see “Noctilucent Clouds.ppt”)