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We are now acting because the risks of inaction would be far greater.

We are now acting because the risks of inaction would be far greater. G.W. Bush’s Speech on Iraq March 16 2003

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We are now acting because the risks of inaction would be far greater.

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  1. We are now acting because the risks of inaction would be far greater. G.W. Bush’s Speech on Iraq March 16 2003 To me the question of the environment is more ominous than that of peace and war. We shall have regional conflicts and use of force, but world conflicts I do not believe will happen any longer. But the environment, that is a creeping danger. I’m more worried about global warming than I am of any major military conflict.” Hans Blix in an interview on MTV News, Reported in New York Times, Sunday March 15 2003 “Hans Blix’s Greatest Fear”

  2. Energy Balance

  3. Since 1800: Atmospheric CO2 has increased by 30% Increase in temperature // increase in greenhouse gases

  4. Climate Forcing:expressed as a change in radiative heating (W/m2) at surface for a given change in trace gas composition or other change external to the climate system Cumulative climate forcing since 1800 Hansen PNAS 2001

  5. Forced Cloud Changes:anthropogenic aerosols may act ascloud condensation nuclei Sep 11 2001: Air Force One + 9 military jets Jet contrails stimulated growth of cirrus clouds 5 hrs later Jan 26 2001 Typical day: 700-800 planes

  6. Decreasing area of snow and ice 1500 2000 • Signal of warming • Climate feedback: • Increase surface albedo • Increase absorption of solar irradiance • Increase temperature

  7. “Forced” vs “Natural” climate change Instrumental Temperature Trends Glacial-interglacial 10 K /10,000 yr = 1 K/1,000 yr AD 1000-1600: 0.9K / 600 yr = 0.15K /100 yr Cannot be ruled out AD 1980-2000: 0.5 K / 20 years No evidence of abrupt “natural” climate change Uncertainty: natural climate variability on 102 - 103 years; abrupt climate change For the next 100 years, natural variability unlikely to exceed 0.5K Anthropogenically-forced climate change is real

  8. Climate Forcing and Climate Feedbacks:A given change in “external” climate forcing (e.g. 2xCO2) will trigger changes in the hydrologic system, atm circulation. These “internal” changes will act to amplify or damp the initial forcing. CO2: 300  600 ppmv CO2: 300  200 ppmv Change in surface air temperature Last Glacial Maximum • DT_realized = feedback factorx DT_forcing • feedback factor ~ 3.5 • Smaller feedback factor cannot explain cooling during the Last Glacial Maximum • Without CO2 decrease, cannot explain cooling during the Last Glacial Maximum

  9. Energy Balance

  10. Climate Change Signal

  11. Climate Response • Warming not globally uniform • High-latitude amplification  Albedo feedback

  12. Global Climate Models used to project climate change from different CO2 scenarios: Business as usual CO2 emission Stabilization of CO2 Control

  13. Holdridge Bio-Climate Classification Climate change will alter the distribution of biomes

  14. UN Framework Convention on Climate Change • Ultimate objective: stabilizing greenhouse gas concentrations in the atmosphere that would prevent dangerous anthropogenic (human-induced) interference with the climate system • Such a level should be achieved within a time frame to allow ecosystems to adapt naturally to climate change,to ensure that food production is not threatened, and to enable economic development to proceed in a sustainable manner

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