Global Warming Projections for the IPCC SAR and TAR using simple models Sarah Raper.

Global Warming Projections for the IPCC SAR and TAR using

simple modelsSarah Raper

Model for the Assessment of Greenhouse-gas Induced Climate Change (MAGICC)

IPCC SAR version

IPCC TAR version

New features include: Carbon-cycle feedbacks Forcing updated to be consistent with TAR chapters Climate model tuning to reproduce specific AOGCM results AOGCM consistent sea level

Gas-cycle models Climate

modelTemperature

changeSea level

rise

IS92 emissions

6 scenarios

Funded by DETR

Radiative forcing

Gas-cycle models Climate

modelTemperature

change

SRES emissions

35 scenarios

Radiative forcing

Sea level rise

A2A1

B1 B2

Economic

Socio-Economic Scenarios

RegionalGlobal

Environmental

B - balancedFI - fossil intensiveT - non-fossil

Well-mixedATMOSPHERE

concentration

Anthropogenicemissions

Natural emissions

Schematic treatment of well mixed gases

Removal processes proportional to concentration

UD model

Energy balance climate model

ΔQ=λΔT+ΔF

ΔQλΔTΔF

External forcing (Wm-2)Feedback term (Wm-2)

Heat flux from bottom of the atmosphere (Wm-2)

At equilibrium ΔF = zeroAt 2xCO2 ΔQ2xΔQ=

The climate sensitivity, ΔT2x =ΔQ2x

λ

The CMIP2 data set

Climate Model Intercomparison project

Model forcing is a 1% compound increase in CO2

0

0.5

1

1.5

2

2.5

3

3.5

4

4.5

GFDL CGCM1 CSIRO HadCM3 HadCM2 ECHAM3 CSM PCMModel

Effective climate sensitivity (oC)Ocean heat flux (Wm-2)Temperature change (oC)

Results of CMIP2 analysis

-12

-10

-8

-6

-4

-2

0

Model

NO DATA

Shows changes in the THC in the CMIP2 data at the time of CO2 doubling.

Comparison of effects on temperatureProjections of SAR and TAR high and low emissions scenariosand science methods

•Differences can be divided into the emissions scenarios and the science

•The main source of emissions-related differences is aerosol forcing•The TAR science leads to slightly lower total forcing and slightly larger warming

•For the low scenarios the effects are roughly equal, both leading to higher warming•For the high scenarios the main effect is due to the new emissions scenario

0

1

2

3

4

5

6

7

8

9

1990 2000 2010 2020 2030 2040 2050 2060 2070 2080 2090 2100

YEAR

RADIATIVE FORCING (W/m

2)

TAR

TAR

TAR

TAR

OLD

SAR

SAR

A1C

92e

B1

92c

Radiative forcing for low and high estimates of global-meanWarming given in the IPCC SAR and TAR

From Wigley and Raper J of Climate (in press)

0

1

2

3

4

5

6

1990 2000 2010 2020 2030 2040 2050 2060 2070 2080 2090 2100

YEAR

GLOBAL-MEAN TEMPERATURE CHANGE (

oC)

OLD

TAR

TAR

SAR

TAR

TAR

SAR

A1C

92e .

B1

92c

Low and high estimates of global-mean warming given in the IPCC SAR and TAR From Wigley and Raper J of Climate (in press)

Sea level rise

Parameters to be considered

Thermal expansionLand based ice -

GreenlandAntarcticaGlaciers and icecaps

Changes in permafrostEffect of sediment depositonLong-term adjustment of icesheets

Projected global-average sea-level rise for the IS92a scenario (IPCC 2001)

Projections of total sea-level rise 1990-2100 (IPCC 2001)

SRES scenarios

Co2 Forcing Effect

Relationship between CO2 concentration (C) and forcing is

ΔQ = α ln(C/Co)

S = ΔT2X/ΔQ2X

ΔQ is the forcing change due to concentration change from C0 to C SAR = 6.3, TAR = about 5.31

ΔT2X is the equilibrium CO2 doubling temperature changeS is the sensitivityIf is reduced but ΔT2X is not, then the radiative forcing dueto CO2 is reduced, while the true climate sensitivity is increased