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AOS 101 Climate Change: Introduction March 4/6 100 BIG PICTURE heat budget of earth and atmosphere 30 SPACE 12 58 ATMOSPHERE 20 Shortwave 50 Longwave 102 7 94 GROUND Conduction Convection 23 Latent Heat “GREENHOUSE” EFFECT 12 58 CH4 N2O CO2 H2 O 102 Longwave 94 • 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 GROUND 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. 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 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. 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. 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). 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. 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.