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CESDSAGES Scottish Alliance for Geoscience, Environment &
Society
Observing and Modelling Climate Change
Prof. Simon Tett, Chair of Earth System Dynamics & Modelling: The University of Edinburgh
CESD
Outline
• Observing Climate Change
• Modelling Climate
• Causes of Historical Climate Change
• Projections of Future Climate Change
CESD
Observing Climate Change:What is the problem?
• Observing system not stable
• Climate changes slowly
• Examples:
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100 0.0740.018
50 0.1280.026
Warmest 12 years:1998,2005,2003,2002,2004,200
6, 2001,1997,1995,1999,1990,200
0
Period Rate
Years /decade
From Kevin E. Trenberth, NCAR
Global mean temperatures are rising
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Sea-ice (its ½ what it was)
Is this unexpected? Are we missing something fundamental in our understanding of the Earth system?
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Climate Modelling
• Climate modelling has long history – first attempts made in 1950’s.– Developed from numerical weather prediction
• Which is how weather forecasting is done
– Take physical laws and apply them to atmosphere and oceans.
– But now very complex.
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Karl and Trenberth 2003
Modelling the Climate System
Main Message: Lots of things going on!
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HadCM3
20 Ocean Levels
19 Atmospheric LevelsAtmospheric resolution: 3.75 by 2.5
Ocean resolution :1.25 by 1.25
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Many important processes occur on scales below that explicitly
modelled.
What is there… How we model
Uncertainties how to do this lead to uncertainties in prediction of climate change
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Natural Factors that might effect climate
20001850
Volcanic Aerosol depth
0
0.2
Volcanoes inject aerosol into the upper atmosphere where it stays for 2-3 years. There it scatters sunlight back to space cooling the planet
1700 2000
200
0
Sunspot NumberThe sun may be a variable star with amount of energy reaching the earth changing over decades
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Important Human Factors
2000
Ice cores
Flasks
1700 1800 1900 2000Year
600
800
1000
1200
1400
1600
1800Mauna Loa
Observatory
Ice cores1700 1800 1900
Year
260
280
300
320
340
360
380CO2 MMR*106 CH4 MMR*109
Greenhouse gas concentrations have changed over the last century.
As have emissions of sulphur and other aerosols
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Attribution
• are observed changes consistent with
expected responses to forcings
inconsistent with alternative explanations
Observations
All forcing
Solar+volcanic
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Understanding and Attributing Climate Change
Continental warming
likely shows a significant anthropogenic contribution over the past 50 years
CESDProjections of Future Changes in Climate
Best estimate for low scenario (B1) is 1.8°C (likely range is 1.1°C to 2.9°C), and for high scenario (A1FI) is 4.0°C (likely range is 2.4°C to 6.4°C).
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Projected warmingin 21st century expected to begreatest over land and at most high northern latitudesand least over the Southern Ocean and parts of the North Atlantic Ocean
Projections of Future Changes in Climate
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Projections of Future Changes in Climate
Precipitation increases very likely in high latitudes
Decreases likely in most subtropical land regions
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Extreme events
Tewkesbury 2007Photograph: Daniel Berehulak/GettyImages
Met Office provisional figures show that May to July in the England and Wales Precipitation is the wettest in a record that began in 1766.
We must learn from the events of recent days. These rains were unprecedented, but it would be wrong to suppose that such an event could never happen again…. (Hazel Blears, House of Commons, July 2007)
Is it human induced climate change or natural variability?