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”

3. Energy Balance

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

5. Climate Forcing: expressed as a change in radiative heating (W/m 2 ) at surface for a given change in trace gas composition or other change external to the climate system Hansen PNAS 2001 Cumulative climate forcing since 1800

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

7. 15002000 Signal of warming Climate feedback: Increase surface albedo Increase absorption of solar irradiance Increase temperature Decreasing area of snow and ice

8. “Forced” vs “Natural” climate change Uncertainty: natural climate variability on 10 2 - 10 3 years; abrupt climate change For the next 100 years, natural variability unlikely to exceed 0.5K Anthropogenically-forced climate change is real 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

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

10. Energy Balance

11. Climate Change Signal

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

13. Global Climate Models used to project climate change from different CO 2 scenarios: Business as usual CO 2 emission Stabilization of CO 2 Control

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

16. 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

17. 1988Intergovernmental Panel on Climate Change (IPCC) estab. 1990IPCC 1 st Assessment Report  real threat that by mid 21 st century human actions will have changed the basic conditions that permit life Intergov Negotiating Ctte (INC) estab. 1992UN Framework Convention on Climate Change (UNFCCC) estab; “Earth Summit in Rio de Janeiro; Convention open for signatures 1994UNFCCC came into force: recognition that climate change is a real problem 1995IPCC 2 nd Assessment Report  evidence for human-induced climate change; estimate “permissible emissions” to stabilize CO 2 at 450 ppmv, 600 ppmv,...; assessment of impacts of climate change 1997COP3: Kyoto Protocol; developed countries to reduce their collective emissions of 6 GHG’s (from 1990 levels) by at least 5% by 2008-2012 1998Kyoto Protocol open for signatures; 84 obtained in one year 2001IPCC 3 rd Assessment Report  more evidence for human-induced climate change 2002World Summit on Sustainable Development; Johannesburg