The Modeling of Climate and
Climate Change;
can we trust model predictions?
University of California, Irvine
21 February 2003
by
John Houghton
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Outline
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
Introduction

Cloud Radiation Feedback

Ocean Interactions

The Carbon Cycle

The Climate of the 20th Century

Climate Projections for the 21st Century

Regional Climate Modeling

Patterns of Climate Response
The greenhouse effect
Solar radiation
Long-wave
radiation
236 Wm-2
236 Wm-2
Equivalent T = 255 K (-18ºC)
390 Wm-2
T = 255 K (-15ºC)
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Spectra of
outgoing
radiation from
Earth
observed by
IRIS on
Nimbus 3
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The Enhanced Greenhouse Effect
Solar (S) and longwave (L) radiation in Wm-2 at the top of the atmosphere
S
L
S
L
S
L
S
L
236
236
236
232
236
236
236
236
T = -18°C
CO2 x 2
+ Feedbacks
CO2 x 2
CO2 x 2
H2O (+60%) Ice/Albedo
(+20%)
Cloud?
Ocean?
TS = 15°C
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TS = 15°C
DTS ~ 1.2K
DTS ~ 2.5K
The climate system
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The Development of Climate models,
Past, Present and Future
Mid 1970s
Mid 1980s
Early 1990s
Late 1990s
Present day
Atmosphere
Atmosphere
Atmosphere
Atmosphere
Atmosphere
Atmosphere
Land surface
Land surface
Land surface
Land surface
Land surface
Ocean & sea-ice
Ocean & sea-ice
Ocean & sea-ice
Sulphate
aerosol
Sulphate
aerosol
Non-sulphate
aerosol
Sulphate
aerosol
Non-sulphate
aerosol
Carbon cycle
Carbon cycle
Ocean & sea-ice
Early 2000s?
Atmospheric
chemistry
Ocean & sea-ice
Off-line
model
model
development
Strengthening colours
denote improvements
in models
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Sulphur
cycle model
Land carbon
cycle model
Ocean carbon
cycle model
Atmospheric
chemistry
Non-sulphate
aerosols
Carbon
cycle model
Atmospheric
chemistry
Predicting impacts of climate change
Emissions
Scenarios from population, energy,
economics models
Concentrations
Carbon cycle and chemistry models
CO2, methane, sulphates, etc.
Global climate change
Coupled global climate models
Temperature, rainfall, sea level, etc.
Regional detail
Regional climate models
Mountain effects, islands, extreme weather, etc.
Impacts
Flooding, food supply, etc.
Impacts models
The main stages required to provide climate change scenarios for assessing the impacts of climate change.
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Hadley Centre - PRECIS brochure
Coupled atmosphere / ocean climate model
Radiation
Atmosphere:
Density
Motion
Water
Heat
Exchange of: Momentum
Water
Ocean: Density (inc. Salinity)
Motion
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Sea
Ice
Land
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19 levels in
atmosphere
THE HADLEY
CENTRE
THIRD
COUPLED
MODEL -
1.25
1.25
20 levels
in ocean
HadCM3
-5km
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30km
2.5
lat
3.75
long
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Physical Feedbacks
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
Water vapour

Ice albedo

Clouds

Oceans

Ice sheets
Cloud Radiation Feedback
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Cloud radiation feedback
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Global average change in T /C
Greenhouse Gases
Clouds
Change in T
None
As Now
As Now
As Now
X2 CO2
X2 CO2
As Now
None
+3% high
+3% low
As Now
+ feedbacks
-32
4
0.3
-1
1.2
2.5
Model Estimates of Cloud Radiative Forcing
with CO2 Doubling
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Effect of cloud feedback formulation
on climate prediction

Feedback scheme
Global Av Temp change,C
for doubled CO2
– RH
5.3
– CW
2.8
– CWRP
1.9
– after Senior & Mitchell, Hadley Centre
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Net cloud forcing: January to July
Hadley Centre
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SHIP TRACKS UNDER CLOUD
Washington
state
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Ocean Interactions
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IPCC Synthesis Report
Strength of the thermohaline circulation in the North Atlantic.
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Hadley Centre
Modelled transport of water in
Atlantic conveyor belt
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IPCC Third Assessment Report
Projected changes in annual temperatures for the
2050s
BW 11
The projected change in annual temperatures for the 2050s compared with the present day,
when the climate model is driven with an increase in greenhouse gas concentrations
equivalent to about 1% increase per year in CO2
The MetOffice. Hadley Center for Climate Prediction and Research.
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Changes in surface air temperature, relative to the present day, 20 years after the
hypothetical collapse of the thermohaline circulation.
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Hadley Centre
Combined effect of THC collapse
(2049-2059) and global warming
Surface Temperature
Cooling over UK: 1-3°C
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The Carbon Cycle
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IPCC Third Assessment Report
Human Perturbation of the Carbon Cycle
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Partitioning of CO2 uptake using O2 measurements
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Global CO2 budgets in GtC per year
1980s
1990s
Atmospheric increase
3.3 ± 0.1
3.2 ± 0.1
Emissions (fossil fuel, cement)
5.4 ± 0.3
6.3 ± 0.4
Ocean-atmosphere flux
-1.9 ± 0.6
-1.7 ± 0.5
Land atmosphere flux
-0.2 ± 0.7
-1.4 ± 0.7
partitioned as follows:
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Land-use change
1.7 (0.6 to 2.5)
NA
Residual terrestrial sink
-1.9 (-3.8 to 0.3)
NA
IPCC Third Assessment Report
Carbon cycle feedbacks
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Change in carbon
content of soil (top)
and vegetation
(bottom)
between 1860 and
2100
- predicted by
Hadley Centre
climate model
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Hadley Centre
Simulated changes in the global total soil and vegetation carbon content (Gt C) between 1860 and 2100.
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Hadley Centre
Influence of ENSO on CO2 Variability

Annual changes in
atmospheric CO2 are
dominated by ENSO
– after removing
anthropogenic rise
– rise during El Nino
– fall during La Nina
DCO2 - black, Nino3 - red
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Influence of Volcanoes on CO2 Variability

2 notable exceptions
to ENSO correlation
El Chichon

CO2 levels lower
than expected

Coincide with major
volcanic eruptions
Pinatubo
DCO2 - black, Nino3 - red
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Constraint from ENSO Sensitivity
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
Model with q10=2 has
realistic sensitivity to
ENSO.

Reconstructions for
range of q10.

Infer q10=2.1±0.7.
Constraint from Sensitivity to Volcanoes

Model with q10=2 has
realistic sensitivity to
Pinatubo.

Reconstructions for
range of q10.

Infer q10=1.9±0.4
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ENSO and Pinatubo Variations as a constraint on
climate-carbon cycle feedback
Model with
C cycle
Feedback
(q10= 2)
Grey region is estimate of uncertainty
related to q10 parameter for soil respiration
Model without
C cycle
Feedback
q10= 3
q10= 1
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Photo: Tim Hewison
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Estimated carbon uptake if
suitable arable land north of
30º N were to be replaced with
trees.
The additional effect on climate
of the changes in surface
reflectivity when trees are planted
on suitable arable land north of
30º N, expressed as equivalent
carbon emissions.
The difference between the
two diagrams above. Negative
values show where the net
effect of planting trees is to
warm climate.
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Hadley Centre
NET EFFECT OF PLANTING TREES
expressed as equivalent carbon uptake
–50
Met Office / Hadley Centre
0
50
100
150
tonnes of carbon per hectare
200
Negative values show where the net effect
of planting trees is to warm climate
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EMISSIONS AND CONCENTRATIONS OF CO2
from unmitigated and stabilising emission scenarios
1000
950
CO2 concentration (ppm)
Anthropogenic CO
2 emissions (GtC/yr)
20
15
10
5
900
850
800
750
700
650
600
550
500
450
400
0
2000 2050 2100 2150 2200 2250 2300 2350
Unmitigated emissions
350
2000 2050 2100 2150 2200 2250 2300 2350
750 ppm stabilisation
550 ppm stabilisation
Source: IPCC
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The Climate of the 20th
Century
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Global mean surface air temperature anomalies from 1,000 year control simulations with three different
climate models, - Hadley, GFDL and Hamburg, compared to the recent instrumental record. No model
control simulation shows a trend in surface air temperature as large as the observed trend. If internal
variability is correct in these models, the recent warming is likely not due to variability produced within the
climate system alone.
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IPCC Third Assessment Report
Simulated annual global mean surface temperatures
Natural forcing
Anthropogenic
forcing
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Simulated annual global mean surface temperatures
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IPCC statements on Detection
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
“The balance of evidence suggests a
discernible human influence on global
climate”
1995 Report

“There is new and stronger evidence that
most of the warming observed over the
last 50 years is attributable to human
activities”
2001 Report
Climate Projections
for the 21st century
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The solid line shows a GCM prediction of temperature change. Prior to 1990, historical emissions were
used. Beyond 1990, the IS92a emissions scenario was used. The dashed line shows the results of
scaling the model prediction to give the best fit to the most recent 50 years of observations. The shaded
region is the uncertainty estimate.
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Hadley Centre
SRES scenario familys
More
economic
A1
More
global
B: balanced
FI: fossil intensive
T: non-fossil
B1
A2
More
regional
B2
More
environmental
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Globally averaged tempertaure
change for scenario SRES B2
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IPCC Third Assessment Report
Globally averaged precipitation
change for scenario SRES B2
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IPCC Third Assessment Report
Area averaged changes in summer rainfall for the period 2071-2100 over southern Asia as
predicted by nine coupled models forced by the A2 emissions scenario (taken from Chapter
10 of the Scientific Basis of the IPCC Third Assessment Report). In other areas predictions
can show much greater differences in magnitude and even sign.
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Hadley Centre - PRECIS brochure
Observed and projected changes in extremes
Confidence in observed
changes (latter half
of the 20th century)
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Changes in Phenomenon
Confidence in projected changes
(during the 21st century)
Likely
Higher maximum temperatures and
more hot days over nearly all land areas
Very likely
Very likely
Higher minimum temperatures, fewer
cold days and frost days over nearly all
land areas
Very likely
Very likely
Reduced diurnal temperature range
over most land areas
Very likely
Likely, over many areas
Increase of heat index over land areas
Very likely, over most areas
Likely, over many Northern
Hemisphere mid- to highlatitude land areas
More intense precipitation events
Very likely, over many areas
Likely, in a few areas
Increased summer continental drying
and associated risk of drought
Likely, over most mid-latitude continental
interiors (Lack of consistent projections
in other areas)
Not observed in the few
analyses available
Increase in tropical cyclone peak wind
intensities
Likely, over some areas
Insufficient data for
assessment
Increase in tropical cyclone mean and
peak precipitation intensities
Likely, over some areas
58
IPCC Third Assessment Report
Simulated temperature rise and thermal
expansion for the 4xCO2 experiment
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Regional Climate Modelling
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Schematic diagram of the resolution of the Earth’s surface and the
atmosphere in the Hadley Centre regional climate model.
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Hadley Centre - PRECIS brochure
Regional Climate Model
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
High resolution (50km) over limited area (Europe,
Indian subcontinent)

Embedded in global model, so subject to same
uncertainties

Takes account of local characteristics, e.g.
mountains, coasts

Better regional detail, better prediction of
extremes in weather (eg flooding)

Everybody wants one!
The representation of the Philippines in RCMs with resolutions of 400 km (the GCM), 50 km and 25 km.
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Hadley Centre - PRECIS brochure
Patterns of present-day winter precipitation over Britain. Left, as simulated with the global
model. Middle: as simulated with the 50 km regional model. Right, as observed.
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Hadley Centre - PRECIS brochure
The frequency of winter days over the Alps with different daily rainfall thresholds.
Purple bars, observed. Dark red bars simulated by the GCM. Green bars
simulated by the RCM.
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Hadley Centre - PRECIS brochure
A tropical cyclone is evident in the mean sea-level pressure field from the RCM (right) but not in the driving
GCM (left) for the corresponding day (from an RCM over southern Africa, developed by the Hadley Centre
in collaboration with the university of Cape Town).
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Hadley Centre - PRECIS brochure
Predicted changes in summer surface air temperatures between the present day and the end of the 21st
century. Left, from the global model. Right, from the regional model.
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Hadley Centre - PRECIS brochure
Predicted changes in monsoon precipitation over India, between the present
day and the middle of the 21st century from the GCM (left) and the RCM (right).
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Hadley Centre - PRECIS brochure
Is the Climate Chaotic?
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