chapter - Atmospheric and Oceanic Science

Climate scenarios
From Table 12.2 it comes out that there would not be much difference between
scenarios up to year 2040. That is, no matter what the emission scenario would be,
climate changes up to that date would already be determined. However, the different
options about emissions would be highly critical in the determination of the climate
for the rest of the century.
GCM projections indicate that the continental areas will warm faster and than
oceans; the temperature increase of the air in the North Atlantic and in the areas
around the Pole in the Antarctic Ocean will be less than in the world average.
Likewise, there will be lower daily amplitude in temperature in many regions since
minimum temperature will rise more than the maximum. Projections indicate a
decrease of the snow and of ice cover in the northern hemisphere. It is important to
highlight that many of these changes concur with trends detected in the observations.
With a set of results from a multi-model GCM ensemble, considering different
scenarios of GHG emissions, it is estimated the average climatic change over
the ensemble and its degree of uncertainty. Figure 12.4 shows the annual mean
changes of the surface temperature and their variation range (standard deviation)
for the period 2071-2100 with respect to 1961-90 for scenarios A2 and B2. The features
of the geographic response are similar for both scenarios but the amplitude of
the climatic change patterns is lower for the simulations corresponding to scenario
B2 than in the A2. The relationship between mean change and standard deviation
increases to lower latitudes while at high latitudes next to the Antarctic continent
has a minimum.
Figure 12.5 shows the relative change in the mean of all models precipitation,
which reveals a general increase in the tropics and the mid and high latitudes, and
a reduction over most of the sub-tropical belts. The areas of decreased precipitation
show a high inter-model variability and therefore little consistency among models,
while at the tropics the change can exceed the standard deviation by a factor of 2.
This is particularly evident over the central and eastern tropical Pacific where the
El Niño-like surface temperature warming is associated with an eastward shift of
positive precipitation anomalies. The A2 and B2 scenario experiments exhibit a relatively
large increase in precipitation over the Sahara and Arabia, but with large
inter-model variability. This is partly an artifact of using percentage change rather
than absolute values, since in these regions the annual precipitation total is very
small. In particular, over South America, it is also interesting to notice that the
North and Northeast Brazil show negative precipitation anomalies in the future projection
while the Southeast of the South America and particularly over the La Plata
basin, the rainfall tends to increase.
In the case of the sea level pressure between the period 2071-2100 relative to
1961-90 (Fig. 12.6), the most relevant feature resulting of the ensemble of different
models is the reduction of the pressure in high latitudes and the increase in mean
latitudes. On the other hand, several studies on the southern hemisphere show that
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