The Modeling of Climate and Climate Change can we trust model predictions

1
The Modeling of Climate and Climate Changecan
we trust model predictions?

• University of California, Irvine
• 21 February 2003
• by
• John Houghton

2
Outline

• 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

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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)
4
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 236 236
S L 236 232
S L 236 236
S L 236 236
T -18C
CO2 x 2 Feedbacks H2O (60) Ice/Albedo
(20) Cloud? Ocean?
CO2 x 2
CO2 x 2
TS 15C
TS 15C
DTS 1.2K
DTS 2.5K
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The climate system
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The Development of Climate models, Past, Present
and Future
Mid 1980s
Early 1990s
Late 1990s
Present day
Early 2000s?
Mid 1970s
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
Ocean sea-ice
Sulphate aerosol
Sulphate aerosol
Sulphate aerosol
Non-sulphate aerosol
Non-sulphate aerosol
Carbon cycle
Carbon cycle
Atmospheric chemistry
Sulphur cycle model
Non-sulphate aerosols
Ocean sea-ice model
Off-line model development Strengthening
colours denote improvements in models
Land carbon cycle model
Carbon cycle model
Ocean carbon cycle model
Atmospheric chemistry
Atmospheric chemistry
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Predicting impacts of climate change

• Emissions
• Concentrations
• CO2, methane, sulphates, etc.
• Global climate change
• Temperature, rainfall, sea level, etc.
• Regional detail
• Mountain effects, islands, extreme weather, etc.
• Impacts
• Flooding, food supply, etc.

Scenarios from population, energy, economics
models
Carbon cycle and chemistry models
Coupled global climate models
Regional climate models
Impacts models
The main stages required to provide climate
change scenarios for assessing the impacts of
climate change.
Hadley Centre - PRECIS brochure
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Coupled atmosphere / ocean climate model
Radiation
Atmosphere Density Motion Water
Heat Exchange of Momentum Water
Ocean Density (inc. Salinity) Motion
Sea Ice
Land
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30km
19 levels in atmosphere
2.5 lat
3.75 long
THE HADLEYCENTRETHIRDCOUPLEDMODEL -HadCM3
1.25
1.25
20 levelsin ocean
-5km
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Physical Feedbacks

• Water vapour
• Ice albedo
• Clouds
• Oceans
• Ice sheets

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Cloud Radiation Feedback
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Cloud radiation feedback
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Global average change in T /C
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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
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Strength of the thermohaline circulation in the
North Atlantic.
Hadley Centre
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Modelled transport of water in Atlantic conveyor
belt
IPCC Third Assessment Report
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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.
Hadley Centre
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Combined effect of THC collapse (2049-2059) and
global warming
Surface Temperature
Cooling over UK 1-3C
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The Carbon Cycle
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(No Transcript)
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IPCC Third Assessment Report
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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 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
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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
Hadley Centre
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Simulated changes in the global total soil and
vegetation carbon content (Gt C) between 1860 and
2100.
Hadley Centre
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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

?CO2 - black, Nino3 - red
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Influence of Volcanoes on CO2 Variability

• 2 notable exceptions to ENSO correlation
• CO2 levels lower than expected
• Coincide with major volcanic eruptions

El Chichon
Pinatubo
?CO2 - black, Nino3 - red
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Constraint from ENSO Sensitivity

• Model with q102 has realistic sensitivity to
  ENSO.
• Reconstructions for range of q10.
• Infer q102.10.7.

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Constraint from Sensitivity to Volcanoes

• Model with q102 has realistic sensitivity to
  Pinatubo.
• Reconstructions for range of q10.
• Infer q101.90.4

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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.
Hadley Centre
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NET EFFECT OF PLANTING TREESexpressed as
equivalent carbon uptake

50
0
50
100
150
200
tonnes of carbon per hectare
Met Office / Hadley Centre
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
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.

IPCC Third Assessment Report
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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

• 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

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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.
Hadley Centre
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SRES scenario familys

• More
• economic

A1
A2
B balanced FI fossil intensive T non-fossil
More regional
More global
B2
B1
More environmental
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Globally averaged tempertaure change for scenario
SRES B2
IPCC Third Assessment Report
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Globally averaged precipitation change for
scenario SRES B2
IPCC Third Assessment Report
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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.
Hadley Centre - PRECIS brochure
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Observed and projected changes in extremes

• Confidence in observed
• changes (latter half
• of the 20th century)
• Likely
• Very likely
• Very likely
• Likely, over many areas
• Likely, over many Northern Hemisphere mid- to
  high-latitude land areas
• Likely, in a few areas

Changes in Phenomenon Higher maximum
temperatures and more hot days over nearly all
land areas Higher minimum temperatures, fewer
cold days and frost days over nearly all land
areas Reduced diurnal temperature range over
most land areas Increase of heat index over land
areas More intense precipitation
events Increased summer continental drying
and associated risk of drought Increase in
tropical cyclone peak wind intensities Increase
in tropical cyclone mean and peak precipitation
intensities
Confidence in projected changes (during the 21st
century) Very likely Very likely Very
likely Very likely, over most areas Very
likely, over many areas Likely, over most
mid-latitude continental interiors (Lack of
consistent projections in other areas) Likely,
over some areas Likely, over some areas
IPCC Third Assessment Report
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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
Earths surface and the atmosphere in the Hadley
Centre regional climate model.
Hadley Centre - PRECIS brochure
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Regional Climate Model

• 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!

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The representation of the Philippines in RCMs
with resolutions of 400 km (the GCM), 50 km and
25 km.
Hadley Centre - PRECIS brochure
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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.
Hadley Centre - PRECIS brochure
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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.
Hadley Centre - PRECIS brochure
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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).
Hadley Centre - PRECIS brochure
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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.
Hadley Centre - PRECIS brochure
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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).
Hadley Centre - PRECIS brochure
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Is the Climate Chaotic?