Global Warming

            
             climate changes are mostly natural variations.
            
             have humans begun to change the climate?.
            
            
            
             spatial scale: local, regional, or global.
             Greenhouse Effect:.
             The Process: not ozone hole.
             it is a natural effect. .
             short-wave radiation from the sun warms the earth.
             little is absorbed by the atmosphere.
             the heated earth emits longwave radiation.
             but gases in atmosphere absorb longwave radiation therefore the Earth is warmed.
             the warming is a natural feature ~ 20C.
             but if we add more gases we will cause more warming. .
             Carbon dioxide .
             is a natural gas. Normal, cyclical nature of the gas. .
             El Nino effect strongly influences the CO2 levels. .
             increasing levels of CO2 since 1958: 0.5% per year - increase. .
             predicted to be 450 PPM by year 2050.
             Human contribution .
             to CO2 production is due to burning of fossil fuels. .
             part of the carbon cycle occurs naturally and is naturally variable. .
             however it is not the only or the most powerful greenhouse gas. .
             Methane (CH4).
             levels are low compared to CO2.
             but 3X more effective. .
             pre-industrial levels of methane: 650 PPB.
             1990: 1650 PPB.
             increasing by 1% per year. .
             Sources of Methane:.
             natural wetlands, rice paddies. .
             termites - through the digestion of cellulose - bacteria in gut uses methane. .
             animals such as cattle (ruminants) and sheep and goats. .
             Nitrous Oxide (N2O).
             pre-industrial levels: 285 PPB.
             1990: 310 PPB.
             increasing at a rate of 0.2 - 0.3% per year. .
             Sources:.
             burning of fossil fuels. .
             increased use of fertilizer use.
             atmospheric residence time of 150 years (CO2 - 10 years). .
             Chlorofluorocarbons (CFCs.
             human manufactured (not naturally occurring) .
             manufactured since the 1930s +40s. .
             impact upon the ozone layer. .
             increase of 4% per year.
             Sources:.
             refrigeration, air conditioning, propellants, aerosols.
             Relative Contribution of the Greenhouse gases.
             CFCs 10-15%.
             CH4 - 12-20%.
             O3 - 8 %.
             N2O - 5%.
             Total: 40-50%.
             CO2: 50-60%.
             Environmental Impacts.
             green plants and the biosphere (natural and domesticated).
             hydrology: Sea-level changes (predicted to rise), ice cap and glacier melting.