Global Warming

Regional patternsof climate change 127

(b)

Change in precipitation for scenario A2

60N

30N

EQ

30S

60S

180 120W 60W 0 60E 120E 180

(b)

Change in precipitation for scenario A2

Change in precipitation

Large increase

Small increase

No change

Inconsistent sign

Small decrease

Large decrease Dec-Jan-Feb

Jun-Jul-Aug

Figure 6.5(Cont.).

Much natural climate variability occurs because of changes in, or
oscillations between, persistent climatic patterns or regimes. The Pacific,
North Atlantic Anomaly (PNA – that is dominated by high pressure over
the eastern Pacific and western North America and which tends to lead to
very cold winters in the eastern United States), the North Atlantic Oscil-
lation (NAO – that has a strong influence on the character of the winters
in north west Europe) and the El Ni ̃no events mentioned in Chapter 5
are examples of such regimes. Important components of climate change
in response to the forcing due to the increase in greenhouse gases can be
expected to be in the form of changes in the intensity or the frequency of
established climate patterns illustrated by these regimes.^14 There is little
consistency at the present time between models regarding projections of
many of these patterns. However, recent trends in the tropical Pacific for
the surface temperature to become more El Ni ̃no-like (see Table 4.1 on