Changes in climateextremes 129
(a)
Cold
Lesscold
weather
Previous
climate
New
climate
Morehot
weather
Average
Increase in mean
Probability of occurrence
Hot
more
cold
weather
record hotMore
weather
(b)
Cold
More
recordcold
weather
Previous
climate
New
climate
More
weatherhot
Average
Increase in variance
Probability of occurrence
Hot
More
record hot
weather
changeLess
for
weathercold
(c)
Cold
Previous
climate
New
climate
Much more
weatherhot
Average
Increase in mean and variance
Probability of occurrence
Hot
More
record hotweather
Figure 6.6Schematic
diagrams showing the
effects on extreme
temperatures when (a) the
mean increases leading to
more record hot weather,
(b) the variance increases
and (c) when both the
mean and the variance
increase, leading to much
more record hot weather.
Northern Hemisphere land areas, suggesting that the situation in Figure
6.6(c) could apply in these areas. An example of this can be found in the
box in Chapter 7 on page 177.
However, the changes that are likely to lead to most impact are those
connected with the hydrological cycle. In the last section it was explained
that in a warmer world with increased greenhouse gases, average pre-
cipitation increases and the hydrological cycle becomes more intense.^16
Consider what might occur in regions of increased rainfall. Often in such
regions with the more intense hydrological cycle the larger amounts of
rainfall will come from increased convective activity: more really heavy
showers and more intense thunderstorms. The result of a study with an
Australian climate model of the effect on rainfall amounts of doubling