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SAGES
Scottish Alliance for Geoscience, Environment & Society
CESD
Observing and Modelling Climate
Change
Prof. Simon Tett, Chair of Earth System Dynamics &
Modelling: The University of Edinburgh
Outline
CESD
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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:
CESD
Global mean temperatures are rising
Warmest 12 years:
1998,2005,2003,2002,2004,2006,
2001,1997,1995,1999,1990,2000
Period
Rate
50 0.1280.026
100 0.0740.018
Years /decade
From Kevin E. Trenberth, NCAR
Sea-ice (its ½ what it was)
CESD
Is this unexpected? Are we missing
something fundamental in our understanding
of the Earth system?
Climate Modelling
CESD
• 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.
Modelling the Climate System
CESD
Main
Message:
Lots of
things
going on!
Karl and Trenberth 2003
HadCM3
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19 Atmospheric Levels
Atmospheric resolution: 3.75 by 2.5
Ocean resolution :1.25 by 1.25
20 Ocean Levels
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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
Volcanic Aerosol depth
0.2
0
2000
1850
Volcanoes inject aerosol
into the upper
atmosphere where it
stays for 2-3 years.
There it scatters
sunlight back to space
cooling the planet
Sunspot Number
200
0
1700
2000
The sun may be a
variable star with
amount of energy
reaching the earth
changing over
decades
Important Human Factors
CESD
380
CO2 MMR*106
Mauna Loa
Observatory
360
1800
1400
320
1200
300
1000
1900
Year
2000
Flasks
1600
340
280
260Ice cores
1700
1800
CH4 MMR*109
Ice cores
800
600
1700
1800
1900
Greenhouse gas
concentrations have
changed over the last
century.
2000
Year
As have emissions of
sulphur and other
aerosols
Attribution
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• are observed
changes
consistent with
expected
responses to
forcings
inconsistent
with alternative
explanations
All forcing
Observations
Solar+volcanic
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Understanding and Attributing Climate
Change
Continental
warming
likely shows a
significant
anthropogenic
contribution
over the past
50 years
Projections of Future Changes in Climate
CESD
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).
Projections of Future Changes in Climate
CESD
Projected warming
in 21st century
expected to be
greatest over land
and at most high
northern latitudes
and least over the
Southern Ocean
and parts of the
North Atlantic
Ocean
Projections of Future Changes in Climate
CESD
Precipitation increases very likely in high latitudes
Decreases likely in most subtropical land regions
Extreme events
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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?