1. The Greenhouse Effect and Global Warming

2. Diffuse Radiation - Clear skies: 80% of insolation reaches the surface - Cloudy skies: 10-45% of insolation may reach the surface

3. The Greenhouse Effect  Popular name for process whereby greenhouse gases in atmosphere absorb longwave radiation from Earth and then emit or counterradiate it back to the surface providing additional heating

4. The Greenhouse Effect (cont’d)  Process acts to warm lower atmosphere by keeping longwave radiation from escaping to space (like insulation holding in heat in a house)  With no atmospheric greenhouse effect, Earth would be much colder: current mean global temp is 15°C (59°F); w/o greenhouse effect, temps would be about -18°C (0°F), which is a difference of 33°C (59°F)...

5. Greenhouse Gases  Gases involved in this process are called greenhouse gases  All are considered trace gases, meaning they only constitute a small percentage of atmospheric content, but they play a very important role  Include CO 2, H 2 O, CH 4, and Water vapor

6. How Do Greenhouse Gases Get into the Atmosphere?  CO 2 : burning of fossil fuels (coal, oil, natural gas) and vegetation, during plant decomposition, during volcanic eruptions  H 2 0: evaporation, evapotranspiration, airplane exhaust, volcanic eruptions  CH 4 : decay of organic matter, human activity (rice cultivation, farm animal wastes, bacterial decay in sewage and landfills, fossil fuel extraction and transportation, and biomass burning)

8. Quick Focus on Carbon Dioxide  Charles Keeling started taking CO 2 observations at Mauna Loa, HI, in 1958  Now 45+ years of observations – what do we see?

9. A Bit More about CO 2

11. Industrial Revolution  1750-Europe, early-mid 1800s in US

13. A Few More Facts  CO 2 and H 2 O vapor considered most important greenhouse gases  CFC-12 absorbs 10,000 times more longwave radiation than CO 2 (adding one CFC-12 molecule is equivalent to adding 10,000 CO 2 molecules) CFC’s: widely used in refrigeration process, formerly major component in aerosol spray cans (banned in 1976 by U.S. EPA)  Liquid water droplet and ice particles in clouds also very important in atmospheric greenhouse effect

14. NOAA’s Viewpoint

15. Global Warming Debate  Its happening…and that is not the debate. Although scientists agree that Earth is getting warmer, there is debate about the impact of human activities  Many think human activity is a major cause, while others claim it’s part of a natural cycle  Data sources and beliefs

16. What Natural Processes Lead to Climate Change?  Changes in solar radiation: solar constant variations, 11-year sunspot cycle  Astronomical changes: 23,000-year precession cycle (wobbling of axis), 41,000-year cycle in axial tilt, 100,000-year cycle in orbital eccentricity (revolution path not always elliptical)  Volcanic activity (Mt. Pinatubo, Philippine Islands, April 1994 – Fig. 3.25, p. 112)  Cloudiness

17. Warming vs. Cooling  Natural cycles can lead to warming or cooling, depending on phase of cycle (solar radiation changes and astronomical changes) or location/time of day in atmosphere (dust from volcanic activity and cloudiness)  All greenhouse gases tend to cause warming (exception is when CFC’s destroy O 3 )

18. Greenhouse Gases and Global Warming

19. What Do the Records Show?  Problem with observations: organized, continuous recording of weather only goes back ~140 years  Have other sources to determine temperature and atmospheric composition 1. Tree rings: 1 ring = 1 yr; wider rings = more tree growth = warmer temperatures, more precipitation 2. Ice cores: drill ice and sample gases in bubbles 3. Oceanic sediment cores: drill ocean floor and look at what’s there (including plankton) 4. Reef cores: similar to #3 5. Pollen: in soil and packrat middens

20. Temperature Records

22. How could global warming affect us?  Rising sea levels – flooding of coastal/low-lying areas, harm water supply, shift in crop patterns  Change in growing seasons  Warmer temps = more evaporation  drier soils  Animal/plant habitat expands or contracts  More cloud cover  Stronger hurricanes farther north/south due to warmer ocean temps