Global Warming

Model projections 119

A1B

A1T

A1FI

A2

B1

B2

IS92a

Scenarios

A1B

A1T

A1FI

A2

B1

B2

IS92a

Scenarios

A1B

A1T

A1FI

A2

B1

B2

IS92a

Scenarios

CO

concentration (ppm) 2

300

4000

3500

3000

2500

N^2

O concentration (ppb)

CH

concentration (ppb) 4

2000

1500

500

450

350

400

300

400

500

600

700

800

900

1000

1100

1200

1300

1980 2000

1980

1980

2020 2040 2060 2080 2100

2000 2020 2040 2060 2080 2100

2000 2020 2040 2060 2080 2100

Figure 6.2Atmospheric

concentrations of carbon

dioxide, methane and

nitrous oxide resulting

from the six illustrative

SRES scenarios and from

the IS 92a scenario.

Uncertainties for each

profile, especially those

due to possible carbon

feedbacks, have been

estimated as from about

−10% to+30% in 2100

In order to assist comparison between models, experiments with
many models have been run with the atmospheric concentration of carbon
dioxide doubled from its pre-industrial level of 280 ppm. The global aver-
age temperature rise under steady conditions of doubled carbon dioxide