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

JTH14 1

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

predictions?University of California, Irvine

21 February 2003by

John Houghton

JTH15 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

JTH15 3

The greenhouse effectLong-waveradiation

236 Wm-2

Equivalent T = 255 K (-18ºC)

390 Wm-2

T = 255 K (-15ºC)

236 Wm-2

Solar radiation

JTH15 4

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

JTH15 5

JTH15 6

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

JTH15 7

The climate system

JTH15 8

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

Atmosphericchemistry

Atmosphericchemistry

Off-linemodeldevelopment

Strengthening coloursdenote improvementsin models

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

JTH15 9

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

JTH15 10

Coupled atmosphere / ocean climate model

Radiation

Atmosphere: DensityMotionWater

HeatExchange of: Momentum

Water

Ocean: Density (inc. Salinity)Motion

SeaIce

Land

JTH15 11

JTH15 12

19 levels in atmosphere

20 levelsin ocean

2.5lat 3.75

long

1.251.25

THE HADLEYCENTRETHIRDCOUPLEDMODEL -HadCM3

30km

-5km

JTH15 13

JTH15 14

Physical Feedbacks Water vapour Ice albedo Clouds Oceans Ice sheets

JTH14 15

Cloud Radiation Feedback

JTH15 16

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

JTH15 18

Model Estimates of Cloud Radiative Forcing with CO2 Doubling

JTH15 19

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

JTH15 20

Net cloud forcing: January to July

Hadley Centre

JTH15 21

SHIP TRACKS UNDER CLOUD

Washingtonstate

JTH14 22

Ocean Interactions

JTH14 23 IPCC Synthesis Report

JTH15 24

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

JTH15 26

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

JTH15 27

Changes in surface air temperature, relative to the present day, 20 years after the hypothetical collapse of the thermohaline circulation.

Hadley Centre

JTH15 28

Surface Temperature

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

Cooling over UK: 1-3°C

JTH14 29

The Carbon Cycle

JTH15 30

JTH15 31 IPCC Third Assessment Report

JTH15 32

Human Perturbation of the Carbon Cycle

JTH15 33

Partitioning of CO2 uptake using O2 measurements

JTH15 34

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

JTH15 35

Carbon cycle feedbacks

JTH15 36

Change in carbon content of soil (top) and vegetation (bottom) between 1860 and 2100 - predicted by Hadley Centre climate model

Hadley Centre

JTH15 37

Simulated changes in the global total soil and vegetation carbon content (Gt C) between 1860 and 2100.

Hadley Centre

JTH15 38

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

JTH15 39

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

JTH15 40

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

ENSO.

Reconstructions for range of q10.

Infer q10=2.1±0.7.

JTH15 41

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

JTH15 42

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

JTH15 44

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.

JTH15 45

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

JTH15 46

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

JTH15 47

The Climate of the 20th Century

JTH15 48

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

JTH15 49

Simulated annual global mean surface temperatures

Natural forcing

Anthropogenic forcing

JTH15 50

Simulated annual global mean surface temperatures

JTH15 51

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

JTH14 52

Climate Projections for the 21st century

JTH15 53

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

JTH15 54

SRES scenario familysMore

economic

More environmental

More regional

More global

B: balancedFI: fossil intensiveT: non-fossil

A1 A2

B2B1

JTH15 55 IPCC Third Assessment Report

Globally averaged tempertaure change for scenario SRES B2

JTH15 56 IPCC Third Assessment Report

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.

JTH15 58

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

IPCC Third Assessment Report

JTH15 59

Simulated temperature rise and thermal expansion for the 4xCO2 experiment

JTH14 60

Regional Climate Modelling

JTH15 61 Hadley Centre - PRECIS brochure

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

JTH15 62

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!

JTH15 63 Hadley Centre - PRECIS brochure

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

JTH15 64 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.

JTH15 65 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.

JTH15 66 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).

JTH15 67 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.

JTH15 68 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).

JTH14 69

Is the Climate Chaotic?