Global Warming

122 Climate changein the twenty-firstcenturyand beyond

1800 1900 2000 2100

Year

0

1

2

3

4

5

6

7

8

9

10

Forcing (W m

−^2

)

A1FI

A1B

A1T

A2

B1

B2

IS92a

Model ensemble

all SRES

envelope

(a)

1800 1900 2000 2100

Year

0

1

2

3

4

5

6

7

Temperature Change ( C)

A1FI

A1B

A1T

A2

B1

B2

IS92a

Several models

all SRES

envelope

Model ensemble

all SRES

envelope

Bars show the

range in 2100produced by

several models

(b)

Figure 6.4Simple model results. (a) Anthropogenic globally averaged radiative

forcing, based on historical information about greenhouse gas and aerosol

concentrations to the year 2000 (see Figure 3.8) and the SRES scenarios to the

year 2100. The shading shows the envelope of forcing that encompasses the full

range of thirty-five SRES scenarios. (b) Historic anthropogenic global mean

temperature change and future changes for the SRES scenarios and the IS 92a

scenario calculated using a simple climate model tuned to seven AOGCMs (with

climate sensitivity in the range 1.7 to 4.2◦C). The darker shading represents the

envelope of the full set of thirty-five SRES scenarios using the average of the

model results (mean climate sensitivity is 2.8◦C). The lighter shading is the

envelope including all seven model projections (the range of model results for

each scenario is also shown by the bars on the right hand side).