Figure 2.33: Changes in
the number of frost days (a, b) and in heat-wave duration (c, d) from Frich et
al. (2001). Panel (a) shows the percent changes in the total number of days with
a minimum temperature of less than 0°C between the first and last half of
the period, approximately 1946 to 1999. The red circles indicate negative changes
and the blue circles indicate positive changes. Panel (c) shows percentage changes
in the maximum number of consecutive days (for periods with >5 such days) with
maximum temperatures >5°C above the 1961 to 1990 daily normal. The changes
are for the first and second half of the period, approximately 1946 to 1999. The
red circles indicate positive changes and the blue circles indicate negative changes.
In both panels, the size of each circle reflects the size of the change and solid
circles represent statistically significant changes. Panels (b) and (d) show the
average annual values of these quantities expressed as percentage differences
from their 1961 to 1990 average values. The trend shown in panel (b) is statistically
significant at the 5% level.