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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

The Earth has warmed (facts)Why it has warmed (theories)Why the theories are believable

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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?