Global Climate Change 4 Climate Change Consequences Climate Change Mitigation Climate Change Politics Tipping points
GAT: we re heating up
Hockey stick graph past 1000 years 2001 Data from thermometers (red) and from tree rings, corals, ice cores, and historical records (blue). The latter are referred to as proxy data. http://www.aip.org/history/climate/
IPCC Reports First Assessment Report in 1990 Second Assessment Report (SAR) in 1995 Third Assessment Report (TAR) in 2001 Fourth Assessment Report (AR4) in 2007
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2007 AR4 Summary for Policymakers Warming of the climate system is unequivocal, as is now evident from observations of increases in global average air and ocean temperatures, widespread melting of snow and ice and rising global average sea level. Global GHG emissions due to human activities have grown since pre-industrial times, with an increase of 70% between 1970 and 2004. Most of the observed increase in global average temperatures since the mid-20th century is very likely due to the observed increase in anthropogenic GHG concentrations.
More Global atmospheric concentrations of CO2, methane (CH4) and nitrous oxide (N2O) have increased markedly as a result of human activities since 1750 and now far exceed pre-industrial values determined from ice cores spanning many thousands of years. Most of the observed increase in global average temperatures since the mid-20th century is very likely due to the observed increase in anthropogenic GHG concentrations. It is likely that there has been significant anthropogenic warming over the past 50 years averaged over each continent (except Antarctica). Advances since the TAR show that discernible human influences extend beyond average temperature to other aspects of climate.
IPCC assessment 2001 The global average surface temperature has increased since 1861. Over the 20th century the increase has been 0.6±0.2 C. Globally, it is very likely (90-99% chance) that the 1990s was the warmest decade and 1998 the warmest year in the instrumental record, since 1861. New analyses of proxy data for the Northern Hemisphere indicate that the increase in the 20th century is likely (66-90%) to have been the largest of any century during the past 1,000 years. There is new and stronger evidence that most of the warming observed over the last 50 years is attributable to human activities.
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2007 LOSU level of scientific understanding
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IPCC Scenarios A1: rapid and successful economic development, in which current distinctions between "poor" and "rich" countries eventually dissolve A2: economic growth is uneven and the income gap between nowindustrialized and developing parts of the world does not narrow B1: high level of environmental and social consciousness combined with a globally coherent approach to a more sustainable development B2: government policies and business strategies at the national and local levels are influenced by environmentally aware citizens, with a trend toward local self-reliance and stronger communities
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Consequences of Global Warming Coastal changes Storms and Floods Changes to ENSO (El Nino-Southern Oscillation) Human Health Impact Biodiversity losses Agricultural changes
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Possible ENSO Changes 2001
Pictures now and then
Mitigation of Global Warming Energy conservation (efficiency) Nuclear energy Renewable energy CO 2 removal/sequestration in industrial processes Seeding the ocean with iron Cool the earth by screening sunlight Re-forestation Iron hypothesis: fertilizing world s oceans with iron to stimulate ocean photosynthesis
Political Issues & Global Warming Kyoto protocol (December 1997) Cut emissions to 94.8% of 1990 levels by 2008-12 Bonn 2001: 186 countries ratify Kyoto protocol some cuts reduced from 5.2% to only 1-3% US produces ~25% of CO 2, has signed but not ratified India is exempted
Kyoto Treaty Status
James Hansen (NASA) Mt. Pinatubo Scientific American, March 2004, p.68. Notes that ice core data show that the change in climate forcing between the ice age and today is about 6.5 W/ m 2. This forcing maintains a global temperature change of 5 degrees C, implying a climate sensitivity of 0.75±0.25 degrees C per W/m 2 Climate models have similar sensitivity Net value of added forcings since 1850 is 1.6±1.0 W/m 2. Evidence 1.6 W/m 2 is approximately correct from agreement between observed climate and calculations. Even more important: heat gain oceans last 50 yrs is consistent with the estimated NET forcing of 0.5 W/m 2 (so most of the imbalance goes to heating the oceans). Suggests: We re sitting on a time bomb Response of ice sheets Last ice agemore than 14,000 km 3 a yr melting of ice 1 meter of sea level per 20 yr for several centuries 1 meter sea level 1 W/m 2 radiative forcing for 12 yrs Time bomb Rise in sea level may lift ice sheets spectacular melting (not in IPCC reports) Warns: Highest level of additional warming should not be more than 1 C ~ 1 W/m 2
Abrupt changes are possible A small forcing can cause a small [climate] change or a huge one. National Academy of Sciences, 2002. http://www.nap.edu/books/0309074347/html/ Richard Alley, Scientific American, November 2004, p.62 Climate has suddenly flip-flopped in the past and will surely do so again From ice core data: huge temperature swings in very short times Other example: Regional droughts for decades (evidence from the past) Change in ocean circulation
Sudden temperature change in Greenland
Ice core data 2001
What now? Kyoto can only be the beginning Much larger reductions are probably necessary Challenge? Yes, but there are also opportunities... (Friedman)