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AOS 101

This introduction to climate change explains the heat budget of the Earth and atmosphere, the greenhouse effect, causes of global warming, positive and negative feedbacks, direct observations of global warming, arguments against, and projections for the future. It also discusses the decisions of adaptation and mitigation.

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AOS 101

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  1. AOS 101 Climate Change:Introduction March 4/6

  2. BIG PICTUREheat budget of earth and atmosphere 100 30 SPACE 12 58 ATMOSPHERE 20 102 7 23 Shortwave 50 94 Conduction Convection Latent Heat Longwave GROUND

  3. “GREENHOUSE” EFFECT • Very little of the Earth’s LW escapes to space. • Most is absorbed by atmospheric trace gases: H2O, CO2, CH4, N2O. • These gases then RE-EMIT radiation back to the earth. • More trace gas  More atmospheric emittance  More energy re-absorbed by the earth  Warmer temperature 12 58 CH4 N2O CO2 H2O 102 94 Longwave GROUND

  4. Causes • CO2 (most important GH gas) has increased • from 280 ppm to 379 ppm since Industrial Revolution • mainly from fossil fuel use • Methane and N2O have increased as well due to agriculture/fossil fuels • Aerosols (e.g. dust) have increased but this would likely lead to cooling. • Variability of incoming solar radiation may also be a factor.

  5. Feedbacks • Positive (Self-amplifying) feedback: • an increase will lead to a further increase through some process. • Population increase = birth rate increase • Negative (Self-limiting) feedback: • an increase will lead to a decrease back to the initial state (homeostasis). • Body temp warms = sweating = cooling

  6. Positive Feedback in the Atmosphere: • Warming earth causes melting of snow/ice = decrease in earth’s albedo (more SW absorbed) = even warmer temperatures Negative Feedback in the Atmosphere: • Warming earth causes more clouds = increase in earth’s albedo (less SW absorbed) = temperature stays nearly the same The fear is that global warming will result in a positive feedback which cause temperatures to increase very rapidly.

  7. Direct Observations of GW • Eleven of the last 12 years rank as the 12 warmest on record (globally). • Atmospheric water vapor has increased. • Oceans have warmed. • Snowpack/glaciers are melting. • Sea levels have risen 15-20 cm over the last century due to expansion and melting.

  8. Arguments against • Correlation does not imply causation. • Natural variability has caused similar magnitude changes in the past. • Data: • temperature data begins ~1800 (end of little ice age) • reliability of tree rings/ice cores (only account for certain regions).

  9. Projections (*IPCC) • 1.1o-6.4oC increase in global temperature over the next century • Permanent Arctic ice may disappear by 2100. • Hot extremes, heat waves, heavy precipitation more common. • 20-60 cm sea level rise by 2100.

  10. Decisions • ADAPTATION • Accept warming planet and make changes as problems arise. • MITIGATION • Try to reverse climate change to prevent negative effects. • Both will cost money.

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