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What we know about climate change
Exeter Climate Systems
University of Exeter
Workers Educational association, 22 November 2008
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What we know about climate change
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Evidence that the Earth has warmed
1 Less iceSmaller glaciers
Less snow coverLess sea-ice2 Higher sea level3 Higher temperatures
Warmer seasHigher air temperature
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Smaller glaciers: Chacaltaya Glacier 1940 2005
Bolivia, 16S, 5260m alt., melts into La Paz
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Smaller glaciers: Change in length of glacier tongues
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Less snow cover: Snow cover 1920 2005
Black line is 10 yr average 5-95% range
h h d (f ) h h d ( h ) h h b l bl d
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Less sea ice: Summer min Arctic sea ice extent 1980 2005
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Warmer seas: Sea surface temperature 1850 2005
Tropical Atlantic relative to 1961 1990 mean
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Higher air temperature: Global Temperature 1850 2000
Rises and accelerates
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Why it has warmed (theories)
1 Natural variability2 Orbital changes3 Brighter sun4 More greenhouse gases
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Natural variability? Summer 2003 was a 5 event
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a t as wa ed ( acts) W y t as wa ed (t eo es) W y t eo es a e be evab e d
Orbital changes? Milankovitch Cycles
Ice ages triggered by especially cold NH summers. No natural iceage expected for 30,000 years.
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( ) y ( ) y
Slightly brighter sun: Total Solar Irradiance 1980 2005
Via satellite measurements
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Slightly brighter sun: Total Solar Irradiance 1600 2000
Reconstructed dataset
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More CO2 from fossil fuels: CO2 and O2 concentrations
CO2 from Mauna Loa and Baring Head, New Zealand
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More greenhouse gases: Greenhouse gases 0 2005
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Greenhouse effect
Like a blanket. Where least GHGs, extra GHG has most effect.
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Greenhouse effect
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Greenhouse effect
1834 Joseph Fourier says atmosphere can retain heat
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Greenhouse effect
1859 John Tyndall says CO2 and H2O are greenhouse gases
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Greenhouse effect
1895 Svante Arrhenius: 40% rise in CO2 can end ice age
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Greenhouse effect
1938 G.S.Callendar: climate sensitivity is 2K, more at poles
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Greenhouse effect
1970s Sulphate aerosol clouds are cooling
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20th Century temperature change
Thick lines: multi-model ensemble mean
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20th Century continental temperature change
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Sources of graphics
Wikipedia commons
BBC Hulton Picture Library
Encyclopaedia Brittanica
G.S. Callendar Archive, UEAAll other graphics are from www.ipcc.ch
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Next
How do we know what we know?