we are now acting because the risks of inaction would be far greater. g.w. bush’s speech on iraq...
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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”
Energy Balance
Since 1800: Atmospheric CO2 has increased by 30%
Increase in temperature // increase in greenhouse gases
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
Hansen PNAS 2001
Cumulative climate forcing since 1800
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
1500 2000
•Signal of warming•Climate feedback:
• Increase surface albedo
• Increase absorption of solar irradiance
• Increase temperature
Decreasing area of snow and ice
“Forced” vs “Natural” climate change
Uncertainty: natural climate variability on 102 - 103 years; abrupt climate changeFor the next 100 years, natural variability unlikely to exceed 0.5K Anthropogenically-forced climate change is real
Instrumental
Temperature TrendsGlacial-interglacial10 K /10,000 yr= 1 K/1,000 yr
AD 1000-1600:0.9K / 600 yr= 0.15K /100 yrCannot be ruled out
AD 1980-2000:0.5 K / 20 yearsNo evidence of abrupt “natural” climate change
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.
T_realized = feedback factor x T_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
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CO2: 300 600 ppmv
CO2: 300 200 ppmv
Last Glacial Maximum
Energy Balance
Climate Change Signal
Climate Response
• Warming not globally uniform• High-latitude amplification
Albedo feedback
Global Climate Models used to project climate change from different CO2 scenarios:
Business as usual CO2 emission
Stabilization of CO2
Control
Holdridge Bio-Climate Classification
Climate change will alter the distribution of biomes
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
1988 Intergovernmental Panel on Climate Change (IPCC) estab.
1990 IPCC 1st Assessment Report real threat that by mid 21st century human actions will have changed the basic conditions that permit life
Intergov Negotiating Ctte (INC) estab.
1992 UN Framework Convention on Climate Change (UNFCCC) estab; “Earth Summit in Rio de Janeiro; Convention open for signatures
1994 UNFCCC came into force: recognition that climate change is a real problem
1995 IPCC 2nd Assessment Report evidence for human-induced climate change; estimate “permissible emissions” to stabilize CO2 at 450 ppmv, 600 ppmv, ...; assessment of impacts of climate change
1997 COP3: Kyoto Protocol; developed countries to reduce their collective emissions of 6 GHG’s (from 1990 levels) by at least 5% by 2008-2012
1998 Kyoto Protocol open for signatures; 84 obtained in one year
2001 IPCC 3rd Assessment Report more evidence for human-induced climate change
2002 World Summit on Sustainable Development; Johannesburg