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Greenhouse Gases - Sources , Sinks, and Trends

Greenhouse Gases - Sources , Sinks, and Trends. Source: Process that adds a GHG to the atmosphere. Sink: Process that takes a GHG out of the atmosphere. Carbon Dioxide (CO 2 ). Natural Sources: Cellular respiration of animals and plants Volcanic eruptions (small source) Forest Fires

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Greenhouse Gases - Sources , Sinks, and Trends

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  1. Greenhouse Gases - Sources, Sinks, and Trends Source: Process that adds a GHG to the atmosphere. Sink: Process that takes a GHG out of the atmosphere.

  2. Carbon Dioxide (CO2) • Natural Sources: • Cellular respiration of animals and plants • Volcanic eruptions (small source) • Forest Fires • Decomposition (decay by microbes) • Natural Sinks • Photosynthesis by plants • Oceans (at air/water interface) • Sedimentary Rock (bottom of oceans) formed from shells, plants, bones etc…..

  3. Currently – more CO2 enters the ocean than leaves it. Problem – Is there a point at which the ocean cannot absorb any more CO2? If so, more CO2 will remain the atmosphere. Long term storage in rock at the bottom of the ocean (dead plants/animals)

  4. Anthropogenic Sources - Combustion of fossil fuels (coal, oil, gas + others) • Interference with Natural Sinks - Deforestation – by removing trees, we are decreasing the ability of Earth to remove CO2 from the atmosphere (reduction of photosynthesis)

  5. Why focus on forests? • Trees remove CO2 and store the carbon for long periods of time! (100s or 1000s of years) • Even after a tree dies, it takes a long time to decay

  6. Slash and Burn in the Amazon Rainforest

  7. Methane (CH4) • Principal component of natural gas (widely used fuel, e.g. home heating) • Natural Sources: - rotting vegetation in wetlands and swamps where there is little O2 - grazing animals (both ends!) • Natural Sinks:- destruction in the atmosphere by hydroxyl ions (OH-)….after about 12 years.

  8. Methane (CH4) • Anthropogenic Sources: - decomposing garbage (landfills) and sewage treatment- rice cultivation (rice paddies)- during extraction of coal/oil/gas- livestock (cattle are the worst)

  9. Why are cows a “human” source? • Livestock populations are not “natural” – their populations are high because humans raise them • Natural populations (caribou etc.) also produce methane but humans do not increase their populations

  10. That’s a lot of cows! This is in the Amazon! Once it was rainforest…….

  11. Rise in CH4 in atmosphere (since the Industrial Revolution)

  12. Halocarbons • CFCs (chloroflourocarbons) • No natural sources • Used in refrigerators, ACs, foams and plastics • Extremely long lasting in the atmosphere (1000s of years) • (note: also depletes ozone layer)

  13. Nitrous Oxide (N2O) • Least contributor as a GHG (due to small quantities) • Car exhaust • Nitrogen-based fertilizers

  14. Water Vapour • Most abundant GHG • Human Activities are not directly increasing water vapour to the atm. • Warmer temperatures DO cause increased evaporation though.

  15. If water vapour increases…… • - less ice cover, less heat reflected, more heat absorbed by land- therefore an overall warming effect • - more white cloud cover, more heat reflected back into space - therefore an overall cooling effect Poorly understood!

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