Regional patternsof climate change 125so can respond more quickly. Listed below are some of the broad fea-
tures on the continental scale that characterise the projected temperature
changes; more detailed patterns are illustrated in Figure 6.5(a). Refer-
ence to Chapter 4 indicates that many of these characteristics are already
being found in the observed record of the last few decades.
Generally greater surface warming of land areas than of the oceans
typically by about forty per cent compared with the global average,
greater than this in northern high latitudes in winter (associated with
reduced sea ice and snow cover) and less than forty per cent in south
and southeast Asia in summer and in southern South America in winter.
Minimum warming around Antarctica and in the northern North
Atlantic which is associated with deep oceanic mixing in those areas.
Little warming over the Arctic in summer.
Little seasonal variation of the warming in low latitudes or over the
southern circumpolar ocean.
A reduction in diurnal temperature range over land in most seasons
and most regions; night time lows increase more than daytime highs.So far we have been presenting results solely for atmospheric tem-
perature change. An even more important indicator of climate change
is precipitation. With warming at the Earth’s surface there is increased
evaporation from the oceans and also from many land areas leading on
average to increased atmospheric water vapour content and therefore also
on average to increased precipitation. Since the water-holding capacity
of the atmosphere increases by about 6.5% per degree celsius,^12 the in-
creases in precipitation as surface temperature rises can be expected to be
substantial. In fact, model projections indicate increases in precipitation
broadly related to surface temperature increases of about three per cent
per degree celsius.^13 Further, since the largest component of the energy
input tothe atmospheric circulation comes from the release of latent
heat as water vapour condenses, the energy available to the atmosphere’s
circulation will increase in proportion to the atmospheric water content.
A characteristictherefore of anthropogenic climate change due to the
increase of greenhouse gases will be a more intense hydrological cycle.
The likely effect of this on precipitation extremes will be discussed in
the next section.
In Figure 6.5(b) are shown the projected changes in the distribution of
precipitation. Although on average precipitation increases there are large
regional variations and large areas where there are likely to be decreases
in average precipitation and also changes in its seasonal distribution. For
instance, at high northern latitudes there are large increases in winter and
over south Asia in summer. Southern Europe, Central America, southern
Africa and Australia are likely to have drier summers.