HS 471 The Atmosphere Chapter 11

1. HS 471The AtmosphereChapter 11

2. Composition of the Atmosphere 78% Nitrogen 21% Oxygen 1% Argon 0.03% Carbon Dioxide Only O2 and CO2 enter biological processes N2 is used by a few species only

3. Troposphere Sea level to 8-9 miles Temperature decreases with altitude (5.4 F / 1000 feet) Where virtually all life occurs Where most weather and climatic phenomena occur Water vapor and dust Stratosphere Temperature slowly increases with altitude (reaches 32  F at 30 miles) No water vapor or dust Ozone layer Mesosphere Temperature decreases with altitude 99 % of the atmosphere lies within 18 miles of the earth’s surface Regions of the Atmosphere

4. Regions of the Atmosphere

5. The atmosphere regulates the quantity and quality of solar radiation that enters and leaves the biosphere Ultraviolet light is generally blocked by ozone layer. UVb goes through, however. Visible light rays goes through the ozone layer but are scattered by atmospheric gas molecules Infrared is ground radiation: Emitted by earth, even at night. Can be absorbed by CO2 and water vapor. What about radiation imbalance??? Radiation Balance

6. Human Impact on the Earth-Atmosphere System Major causes: • Introduction of atmospheric pollutants in unusual amounts • Changing the concentrations of natural atmospheric components Significant impacts: • Ozone depletion • Global warming

7. Stratospheric Ozone Formation

8. Balance: Ozone is formed by UV radiation (daytime) and ozone breaks down to oxygen (nighttime). Chloroflurocarbons (CFCs) – e.g. freons Stable, drift upwards UV radiation breaks down CFCs into chlorine atoms Chlorine atoms react with and destroy ozone One chlorine atom can destroy thousands of ozone molecules Chlorine will persist over 100 years in stratosphere A 1% decrease in ozone layer  increase UV radiation reaching earth by 2%  2-10% increase in cell carcinomas increases in skin melanomas Montreal Protocol 1987: 29 nations agreed to phase out the use of CFCs Developed countries banned CFCs use and production in 1996 Developing countries may still use and produce CFCs until 2010 Are CFC levels dropping in the stratosphere??? Hole in the sky??? Depletion of Ozone Layer

10. Increase in average world temperatures as a result of increased atmospheric concentrations of greenhouse gases. Greenhouse Gases: Carbon dioxide Methane CFCs Nitrous oxides Sources: Burning fossil fuels Includes burning tropical rainforests (25% of all global CO2) Destruction of natural vegetation Cattle Rice cultivation Equilibrium is disrupted over a short period of time Global Warming

11. Regional weather changes Diminishing crop yields Loss of biodiversity Human illness Rising sea levels (by 2010, ¾ of population will live within 36 miles of a coastline) Greenhouse gases are in high enough concentrations to cause an increase in average world temperatures of 2C, relative to its 1990 value, by the end of the 21st century. This would be the warmest climate experienced in the last 10,000 years. Global Warming Effects

12. Greenhouse Policy Debate: United Nations Earth Summit (Rio de Janeiro, 1992) - was the first step. Kyoto, Japan, 1997 Voluntary requests for countries to take action. 171 countries attended Mandatory emission reductions for 38 industrialized countries What about the US??? Reduce greenhouse gases: Improve energy efficiency Replace fossil fuel with alternative sources of energy Reduce CFC emissions and other greenhouse gases Reversing forest loss Global Warming