Climate change - Atmosphere, Weather and Climate - page 401

atmosphere as a result of the necessity for equi-
librium between the incoming solar radiation and the
outgoing terrestrial radiation. The stratosphere and
mesosphere would cool by about 10°C and the
thermosphere by 50°C, for CO 2 doubling, perhaps
causing more frequent noctilucent clouds in the polar
mesosphere.

1300
1200
1100
1000
900

Scenarios
A1B
A1F1
B1
B2

800
700

600

2 A consequent increase in the overall temperature

lapse rate, making the atmosphere more turbulent,
increasing the frequency and intensity of depres-
sions, tropical storms and hurricanes, and making
mid-latitude winter storm tracks more stable in their
positions.

500
400
300

1980 2000 2020 2040 2060 2080 2100

4000

Scenarios
A1B
A1F1
B1
B2

3 Stronger warming of the earth's surface and tropos-

phere in higher latitudes (especially at about 60°
latitude) in late autumn and winter (by 4 to 8°C).

3500

3000

4 A tropical warming of less than the global mean

(i.e. 2 to 3°C). 2500

5 Amplified warming over northern mid-latitude

continents in summer (by 4 to 6°C).

2000

6 Increased precipitation in high latitudes and in the

tropics throughout the year (by 10 to 20 per cent),
and in mid-latitudes in winter (Table 13.4). This
increase is mostly associated with zones of lower
level convergence (i.e. mid-latitude storm tracks and
the ITCZ).

1500

1980 2000 2020 2040 2060 2080 2100

500

Scenarios
A1B
A1F1
B1
B2

450

7 Small changes in the dry subtropics.

8 Soil moisture increases in winter and decreases in

summer in northern mid-latitude continents.

400

9 A reduced extent of sea ice extent and thickness.

350

The 1990 IPCC model was adjusted in 1992 to take
account of the potential cooling effect of anthropogenic
sulphate aerosols; other changes in greenhouse forcing;
a possible slowdown of the thermohaline deep ocean
circulation expected to accompany global warming; an
upper mixed ocean layer 90 m deep with vertical mixing
processes operating at 1 cm 2 s -1 ; revised estimates of
the thermal differences between land and sea; and
improved feedback assumptions, particularly relating
to the effects of cloud cover. Later predictions were
broadly similar to those associated with the 1990 model,
but more moderate. They included a generally greater
warming of the land than of the oceans in winter;
minimal warming, or even cooling, around Antarctica
and in the northern North Atlantic associated with deep
ocean mixing (see Figure 13.19 for the increase by 2040
to 2049 relative to 1880 to 1889). They also showed
rather less warming in high northern latitudes in late

300

1980 2000 2020 2040 2060 2080 2100

Figure 13.17 Predicted changes of CO 2 , CH 4 and N 2 O
between 1980 and 2100 with new scenarios from the Special
Report on Emission Scenarios (SRES). A1F1, A1B and B1 ( see
text).
Note : Units are in parts per million by volume (ppmv), parts per billion
(ppbv) and parts per trillion (pptv), respectively.
Source : Adapted from Houghton et al . (2001). Reproduced by
permission of the IPCC and Cambridge University Press. (Summary
for policy-makers. Report of WG 1, IPCC, p. 65, fig. 18.)

simple model of the upper 50 to 100 m of the ocean. The
major predictions of IPCC 1990 were as follows:

1 A general warming of the earth's surface and tropos-

phere, and a cooling of the stratosphere and upper