Geoscience Reference
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converted into a radiative impact (as shown in Figure
9.16 ) which, in turn, can then be used in the appropriate
model to predict future changes in temperature. These are
shown in Figure 28.2 for three different emission scenarios
and for the periods 2020-29 and 2090-99. B1 is a scenario
assuming a peak global population in mid-century and
with a change towards a service and information economy.
A2 is for a mixed world with an increasing global
population, economic development regionally focussed
and moderate economic growth. A1B is for a world of very
rapid economic growth, population peaking in mid-
century and rapid introduction of new and more efficient
technologies. This scenario is for a balanced energy use
with no heavy reliance on one particular energy source.
Whichever scenario is taken, there is the prediction of an
increase in global temperatures, especially over polar
regions and to a lesser extent over land areas. A mean
increase in global average surface temperature by 2090-99
is about 2 C for B1, 3 C for A1B and 3.5 C for A2.
Projections for precipitation are given with much less
confidence than those of temperature. In some parts of
the world, different models can produce different trends
in precipitation. In Figure 28.3 those areas in which there
is greatest confidence of change are shown in stipple.
Polar regions are expected to experience increased
precipitation as well as some monsoonal areas. One of the
most noticeable decreases in both summer and winter is
in the Mediterranean climate areas of both hemispheres.
The British Isles are in an intermediate position between
these two belts, with a predicted increase of precipita-
tion in winter and a decrease in summer. As we saw in
Chapter 5, warmer temperatures should give greater
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Figure 28.2 Projected surface temperature changes (°C) for the early and late twenty-first century relative to the period
1980-99. Atmospheric-Ocean General Circulation multi-Model average projections for the B1 (top), A1B (middle) and A2 (bottom)
SRES scenarios averaged over decades 2020-29 (left) and 2090-99 (right).
Source: I.P.C.C. 2007
 
 
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