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

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

predictions?University of California, Irvine

21 February 2003by

John Houghton

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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 effectLong-waveradiation

236 Wm-2

Equivalent T = 255 K (-18ºC)

390 Wm-2

T = 255 K (-15ºC)

236 Wm-2

Solar radiation

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Spectra of outgoing radiation from Earth observed by IRIS on Nimbus 3

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The Enhanced Greenhouse EffectSolar (S) and longwave (L) radiation in Wm2 at the top of the atmosphere

S L236 236

T = 18°C

S L236 232

CO2 x 2

S L236 236

CO2 x 2

S L236 236

CO2 x 2+ Feedbacks

H2O (+60%) Ice/Albedo (+20%)

Cloud?Ocean?

TS = 15°C TS = 15°C TS ~ 1.2K TS ~ 2.5K

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The climate system

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The Development of Climate models, Past, Present and Future

Atmosphere Atmosphere Atmosphere Atmosphere Atmosphere Atmosphere

Land surfaceLand surfaceLand surfaceLand surfaceLand surface

Ocean & sea-ice Ocean & sea-ice Ocean & sea-ice Ocean & sea-ice

Sulphateaerosol

Sulphateaerosol

Sulphateaerosol

Non-sulphateaerosol

Non-sulphateaerosol

Carbon cycle Carbon cycle

Atmosphericchemistry

Ocean & sea-icemodel

Sulphurcycle model

Non-sulphateaerosols

Carboncycle model

Land carboncycle model

Ocean carboncycle model



Off-linemodeldevelopment

Strengthening coloursdenote improvementsin models

Mid 1970s Mid 1980s Early 1990s Late 1990s Present day Early 2000s?

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Predicting impacts of climate change

Emissions

ConcentrationsCO2, methane, sulphates, etc.

Global climate changeTemperature, rainfall, sea level, etc.

Regional detailMountain effects, islands, extreme weather, etc.

ImpactsFlooding, 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: DensityMotionWater

HeatExchange of: Momentum

Water

Ocean: Density (inc. Salinity)Motion

SeaIce

Land

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19 levels in atmosphere

20 levelsin ocean

2.5lat 3.75

long

1.251.25

THE HADLEYCENTRETHIRDCOUPLEDMODEL -HadCM3

30km

-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

Global average change in T /CGreenhouse Gases Clouds Change in T

None As Now -32As Now None 4As Now +3% high 0.3As Now +3% low -1X2 CO2X2 CO2

As Now+ feedbacks

1.22.5

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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

Washingtonstate

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Ocean Interactions

JTH14 23 IPCC Synthesis Report

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Strength of the thermohaline circulation in the North Atlantic.

Hadley Centre

JTH15 25 IPCC Third Assessment Report

Modelled transport of water in Atlantic conveyor belt

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Projected changes in annual temperatures for the 2050s

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.

BW 11

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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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Surface Temperature

Combined effect of THC collapse (2049-2059) and global warming

Cooling over UK: 1-3°C

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The Carbon Cycle

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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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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

Global CO2 budgets in GtC per year

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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 NinaCO2 - 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

CO2 - black, Nino3 - red

El Chichon

Pinatubo

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Constraint from ENSO Sensitivity Model with q10=2 has realistic sensitivity to

ENSO.

Reconstructions for range of q10.

Infer q10=2.1±0.7.

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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 without C cycle

Feedback

Model with C cycle

Feedback (q10= 2)

Grey region is estimate of uncertaintyrelated to q10 parameter for soil respiration

q10= 3

q10= 1

JTH15 43Photo: Tim Hewison

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Estimated carbon uptake if suitable arable land north of 30º N were to be replaced with trees.

Hadley Centre

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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NET EFFECT OF PLANTING TREESexpressed as equivalent carbon uptake

tonnes of carbon per hectare–50 0 50 100 150 200

Negative values show where the net effect of planting trees is to warm climate

Met Office / Hadley Centre

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EMISSIONS AND CONCENTRATIONS OF CO2 from unmitigated and stabilising emission scenarios

Unmitigated emissions 750 ppm stabilisation 550 ppm stabilisation

10

5

0

15

20

Ant

hrop

ogen

ic C

O 2 em

issi

ons

(GtC

/yr)

2000 2050 2100 2150 2200 2250 2300 2350

CO

con

cent

ratio

n (p

pm)

2

1000950900850800750700650600550500450400350

2000 2050 2100 2150 2200 2250 2300 2350

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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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 familysMore

economic

More environmental

More regional

More global

B: balancedFI: fossil intensiveT: non-fossil

A1 A2

B2B1


Globally averaged tempertaure change for scenario SRES B2


Globally averaged precipitation change for scenario SRES B2

JTH15 57 Hadley Centre - PRECIS brochure

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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Observed and projected changes in extremesConfidence 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

Not observed in the few analyses available

Insufficient data for assessment

Changes in Phenomenon

Higher maximum temperatures and more hot days over nearly all land areasHigher 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


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Simulated temperature rise and thermal expansion for the 4xCO2 experiment

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Regional Climate Modelling


Schematic diagram of the resolution of the Earth’s surface and the atmosphere in the Hadley Centre regional climate model.

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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!


The representation of the Philippines in RCMs with resolutions of 400 km (the GCM), 50 km and 25 km.


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.


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.


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).


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.


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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Is the Climate Chaotic?

Documents

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