Patterns of climate change across Scotland: technical report - Sniffer

SNIFFER Project CC03: Patterns of Climate Change across Scotland April 2006
The 24-hour or daily maximum and minimum temperature datasets also exhibit a warming
trend. The changes for 24-hour maximum temperature are tabulated for each region and
season below (Table 3). As previously, trends for 1961 to 2004 are shown alongside those
calculated from 1914 to 2004. In the 1961 to 2004 period each region shows a statistically
significant increase in maximum temperature. Moreover, increases in daily maximum
temperature have been consistently greater than those in the mean temperature. However,
the same is not true of the full ninety-year record. Significance is found in the annual mean
figures but not consistently in the seasonal means (only spring in North and East Scotland,
autumn in East Scotland and winter in West Scotland). In addition, since 1914 it is only in
North Scotland that daily maximum temperatures have increased at a faster rate than daily
mean temperatures.
Table 3 - 24-hour maximum temperature changes (°C), for 1961 to 2004 and 1914 to
2004. Statistically significant trends are shown in bold (significant at the 1% level) or italic
(significant at the 5% level) type.
1961-2004 1914-2004
North
Scotland
East
Scotland
West
Scotland Scotland
North
Scotland
East
Scotland
West
Scotland Scotland
Spring 1.16 1.41 1.35 1.29 0.70 0.71 0.48 0.64
Summer 1.11 1.14 1.12 1.12 0.58 0.37 0.20 0.40
Autumn 0.85 0.83 0.83 0.84 0.58 0.66 0.46 0.57
Winter 1.16 1.51 1.47 1.36 0.41 0.58 0.42 0.47
Annual 1.14 1.29 1.25 1.21 0.59 0.60 0.41 0.54
Changes in 24-hour minimum (effectively night-time) temperatures present a more complex
pattern of change (Table 4). As with maximum temperatures all increases since 1961 are
significant, although some increases are at a slower rate than for mean temperatures. Since
1914 there has been a significant upward trend (at the one percent level) in night-time
minimum temperatures in the East and West of Scotland in all seasons except for winter.
These trends are for warming at a rate faster than the mean temperature. In contrast to this,
the average winter minimum temperatures have decreased in North Scotland since 1914,
although none of the winter trends over this period are statistically significant.
Table 4 - 24-hour minimum temperature changes (°C), for 1961 to 2004 and 1914 to
2004. Statistically significant trends are shown in bold (significant at the 1% level) or italic
(significant at the 5% level) type.
1961-2004 1914-2004
North
Scotland
East
Scotland
West
Scotland Scotland
North
Scotland
East
Scotland
West
Scotland Scotland
Spring 0.89 1.08 1.07 1.00 0.46 1.00 0.94 0.76
Summer 1.07 1.18 1.11 1.12 0.30 0.80 0.65 0.55
Autumn 0.55 0.64 0.56 0.58 0.39 1.12 0.99 0.79
Winter 0.96 1.32 1.22 1.15 -0.37 0.35 0.22 0.02
Annual 0.94 1.13 1.06 1.03 0.22 0.84 0.73 0.56
Comparing the data in Tables 3 and 4 it is clear that since 1961 daytime maximum
temperatures have increased at a faster rate than night-time minimum temperatures. This is
contrary to the global trend identified in the IPCC Third Assessment Report (IPCC, 2001).
The IPCC report, based upon analysis of data from 1950 to 1993, showed that, on average,
night-time daily minimum temperatures increased at approximately twice the rate of daytime
daily maximum temperatures. It is interesting to note that extending the period of analysis
back to 1914 shows that the warming trends in maximum and minimum temperature in the
10