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Lecture 15: Projections of Lecture 15: Projections of Future Climate ChangeFuture Climate Change

Global Mean TemperatureGlobal Mean Temperature

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2121stst Century Climate Change Century Climate Change

Dominant influence likely to be increase in Dominant influence likely to be increase in greenhouse gases (anthropogenic)greenhouse gases (anthropogenic)

Projections of temperature change are Projections of temperature change are made using made using climate modelsclimate models

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Climate Models – 1 (Not Climate Models – 1 (Not Necessary)Necessary)

A climate model is a mathematical A climate model is a mathematical representation of the physical processes representation of the physical processes that control climatethat control climate

Equations are complicated: Computers are Equations are complicated: Computers are used to solve themused to solve them

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Climate Models –2 (Not Climate Models –2 (Not Necessary)Necessary)

The most sophisticated climate models The most sophisticated climate models are called are called General Circulation Models General Circulation Models (GCMs)(GCMs)

These models attempt to simulate all These models attempt to simulate all processes in the atmosphere and ocean processes in the atmosphere and ocean relevant to climaterelevant to climate

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Climate Models – 3Climate Models – 3

Climate Model

Anthropogenic forcing

Climate change

Input

Output

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Emission ScenariosEmission Scenarios

Emission scenario: Possible future emissionsEmission scenario: Possible future emissions

Reference: Reference: http://www.grida.no/climate/ipcc_tar/wg1/029.htm

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COCO22 Emissions “Scenarios” Emissions “Scenarios”

10

15

20

25

B1

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Calculation of Future COCalculation of Future CO22

Concentrations -- MethodConcentrations -- Method

Carbon Cycle Model

Anthropogenic Emissions

CO2 Concentration increase

Model Input

Model output

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Projected COProjected CO22 Concentrations for Various Concentrations for Various

Emission ScenariosEmission Scenarios

B1B1

1010

Some Scenario ResultsSome Scenario Results

7007001313““Middle-of-the-road” Middle-of-the-road” scenarioscenario

B2B2

55055055Moderate economic Moderate economic growth; much less growth; much less reliance on fossil fuelsreliance on fossil fuels

B1B1

9809802828Rapid economic growth; Rapid economic growth; strong reliance on fossil strong reliance on fossil fuelsfuels

A1FIA1FI

COCO22

ConcentrationConcentration

in 2100 (ppm)in 2100 (ppm)

Emission Emission Rate in Rate in 2100 2100 (Pg/yr)(Pg/yr)

CharacterizationCharacterizationScenarioScenario

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Past and Projected Future COPast and Projected Future CO22

Concentrations on same graphConcentrations on same graph

See the IPCC Synthesis Report, Summary for Policymakers, Figure SPM-10a, p. 33.

(URL: (URL: http://www.grida.no/climate/ipcc_tar/vol4/englhttp://www.grida.no/climate/ipcc_tar/vol4/english/fig9-1a.htm)ish/fig9-1a.htm)

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Climate Models -- 5Climate Models -- 5

Complication: Models have differing Complication: Models have differing sensitivitiessensitivities

models produce different results for same models produce different results for same emission scenariosemission scenarios

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Differing Response of Models Differing Response of Models for Same Scenariofor Same Scenario

Time

Glo

bal M

ean

Tem

pera

ture

High Sensitivity

Low Sensitivity

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Three Scenarios; three modelsModel 1Model 2Model 3

Scenario A

Scenario B

Scenario C

time

Tem

p(Medium sensitivity)

(High sensitivity)

(Low sensitivity)

Medium emissions

Low emissions

High emissions

Lowest sensitivity, lowest emissions

Highest sensitivity, highest emissions

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Model Projections of Climate ChangeModel Projections of Climate Change

Fig. 9.14 in IPCC Scientific Assessment. Link: http://www.grida.no/climate/ipcc_tar/wg1/353.htm

From 2001 Report

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Summary: Two Causes for Summary: Two Causes for Large Range in ProjectionsLarge Range in Projections

1.1. Wide range in emission scenariosWide range in emission scenarios2.2. Wide range in model sensitivitiesWide range in model sensitivities

#1 due to uncertainty in future human #1 due to uncertainty in future human actions (i.e., it is not a fault of the actions (i.e., it is not a fault of the models)models)

#2 is due to our imperfect understanding #2 is due to our imperfect understanding of the climate system (i.e., it is a fault of the climate system (i.e., it is a fault of the models)of the models)

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From 2007 Report

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Model ProjectionsModel Projections

Average temp. for 2090-2100 compared to Average temp. for 2090-2100 compared to average for 1980 – 1990.average for 1980 – 1990.

All models project warming for all All models project warming for all scenariosscenarios

Range: 1.1Range: 1.1C – 6.4C – 6.4CC

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MeaningMeaning

Low end: warming of 1.1Low end: warming of 1.1CC Achievable Achievable IFIF

1.1. Emissions are cut Emissions are cut significantlysignificantly

2.2. Lowest-sensitivity model is correct Lowest-sensitivity model is correct

High end: Warming of 6.4 High end: Warming of 6.4 CC May occur ifMay occur if

1.1. Emissions continue to rapidly increaseEmissions continue to rapidly increase

2.2. Highest-sensitivity model is correctHighest-sensitivity model is correct

2020

Constant ConcentrationsConstant Concentrations

time

Gre

enh

ouse

-gas

Con

cen

trat

ion

s

tstop

Suppose concentrations of greenhouse gases have been rising, but suddenly stopped rising at time = tstop

2121

time

Tem

per

atu

re

tstop

Temperature Response Temperature Response

Temp. rises as g.h. gases increase

System is not yet in equilibrium

“Realized” warming

2222

Realized WarmingRealized Warming

This is the warming that has been This is the warming that has been observed at time tobserved at time tstopstop

2323

time

Tem

per

atu

re

tstop

Temperature Response Temperature Response

Warming continues until equilibrium is restored

Additional Warming

“Realized” warming

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Warming CommitmentWarming Commitment

Def: Warming that will occur in the Def: Warming that will occur in the future future due to greenhouse gases added due to greenhouse gases added in the in the pastpast Doesn’t include effect of any future Doesn’t include effect of any future

increases in greenhouse gasesincreases in greenhouse gases

2525Published by AAAS

T. M. L. Wigley Science 307, 1766 -1769 (2005)

Fig. 1. CC warming commitment (constant concentrations after 2000) for different climate sensitivities and aerosol forcing levels (L, M, and H on the right of the figure

indicate low, mid-, and high magnitudes for aerosol forcing, respectively)

Low Sensitivity

Medium Sensitivity

High Sensitivity

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Meaning of GraphsMeaning of Graphs

With greenhouse-gas composition With greenhouse-gas composition constant at 2000 levels, Earth would warm constant at 2000 levels, Earth would warm for centuries (warming commitment)for centuries (warming commitment)

Commitment depends on sensitivity and Commitment depends on sensitivity and amount of aerosol forcingamount of aerosol forcing Mid-range estimate: Commitment ~ 0.5Mid-range estimate: Commitment ~ 0.5CC High-end estimate: Commitment ~ 1High-end estimate: Commitment ~ 1CC

This is warming that is “in the pipeline”This is warming that is “in the pipeline”

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Reducing CommitmentReducing Commitment

Only way: Reduce amount of greenhouse Only way: Reduce amount of greenhouse gas in atmospheregas in atmosphere

The sooner the reductions occur, the The sooner the reductions occur, the greater the reduction in the commitmentgreater the reduction in the commitment

Problem: Removing greenhouse gases is Problem: Removing greenhouse gases is very difficult!very difficult!

More later More later

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Principal DifficultyPrincipal Difficulty

COCO22 mixing ratio is 380 ppm mixing ratio is 380 ppm i.e., only 380 out of every million molecules of i.e., only 380 out of every million molecules of

air are COair are CO22

COCO22 removal would require processing removal would require processing

enormous amounts of airenormous amounts of air Lots of energy probably required.Lots of energy probably required.

http://news.bbc.co.uk/2/hi/science/nature/6345557.stm

What the link revealsWhat the link reveals

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Branson launches $25m climate bid

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Another ProblemAnother Problem

Removing CORemoving CO22 would create waste would create waste

Where should it be stored?Where should it be stored?

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Carbon Capture and StorageCarbon Capture and Storage

Would reduce future Would reduce future emissionsemissions, but , but wouldn’t actually wouldn’t actually removeremove CO CO22 from from

atmosphereatmosphere

http://news.bbc.co.uk/2/hi/science/nature/6345557.stm#carbon

Carbon SequestrationCarbon Sequestration

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