Spring temperature trends 1881-2002
The major findings of
UK Climate
Change since 1881 and the 1989 to 2002 warm period in detail
which used data for Central England were that there
was both a long term warming trend in spring and autumn temperatures and a
warming of weather types in these two seasons. However, in winter and summer,
although temperatures were higher than average from 1989 to 2002, this was
accounted for by an increase in warm weather types and there was no warming trend from 1881 to
1988 in these two seasons. A relevant question is: do other UK and European climatological stations show the same seasonal temperature trends? Click on the
hyperlinks in the Table below for graphs portraying seasonal temperature trends.
Table Europe Seasonal
temperature trends since 1881 around Europe
* data only available since 1931
Winter & Summer: most of the climatological
stations above broadly support the trends of Central England of no long
term warming trend from 1881 to 1988 and then a marked warming from 1989 to
2002. Aberdeen is a notable exception where winters have cooled (until 1988) and
summers warmed since 1881.
Spring & Autumn: most of the climatological
stations above broadly support the trends of Central England of a long
term warming trend from 1881 to 2002 and there were marked phases of
warming and cooling of springs and autumns during the second half of the period: warm from 1945 to 1961;
cold from 1962 to 1988; and warm from 1989 to 2002.
These phases and the long term warming of spring weather
types (yellow line) can be seen in this
chart which compares observed spring temperatures 1881 to 2002 with
predictions of spring temperature made using a multiple regression model based
on spring PSC indices (see
UK Climate
Change since 1881 and the 1989 to 2002 warm period in detail for
explanation of PSC indices). The model showed a strong tendency to underestimate
spring temperatures from 1989 to 2002 and this article attempts to find
explanations for this and for the phases of spring temperature since 1945.
Firstly, the correlation coefficients between spring PSC indices
and spring Central England Temperature (CET) 1881 to 2001 are as follows:
P = 0.260** S
= 0.376*** C = -0.296**
** significant at 1% level
*** significant at 0.1% level
Thus, a high incidence of southerly winds is
the most important factor favouring high spring temperatures but anticyclonic
conditions and persistent westerly winds also favour high spring temperatures.
The following tables compare the incidence of PSC indices in quintiles in each
of the three phases of spring temperature since 1945.
Comparison of incidence of P quintiles in each period of springs
|
Number of years |
| |
________________________________________________ |
| |
|
|
|
| P Index |
1945-1961 (warm) |
1962-1988 (cold) |
1989-2002 (warm) |
|
_________________________________________________________________ |
| Above average |
5 |
7 |
5 |
| Average |
4 |
7 |
4 |
| Below average |
8 |
13 |
5 |
|
_________________________________________________________________ |
Main feature(s): no clear trend as both
1945-1961 (warm phase) and
1962-1988 (cold phase) had 48% of springs with above average incidence of easterly winds and below
average incidence of westerly winds.
Comparison of incidence of S quintiles in each period of springs
|
Number of years |
| |
________________________________________________ |
| |
|
|
|
| S Index |
1945-1961 (warm) |
1962-1988 (cold) |
1989-2002 (warm) |
|
_________________________________________________________________ |
| Above average |
10 |
11 |
2 |
| Average |
3 |
3 |
8 |
| Below average |
4 |
13 |
3 |
|
_________________________________________________________________ |
Main feature(s): 59% of springs 1945-1961
(warm phase) had above average incidence of southerly winds and below average
incidence of northerly winds while 48% of springs 1962-1988 (cold phase) had
above average incidence of northerly winds and below average incidence of
southerly winds.
Comparison of incidence of C quintiles in each period of springs
|
Number of years |
| |
________________________________________________ |
| |
|
|
|
| C Index |
1945-1961 (warm) |
1962-1988 (cold) |
1989-2002 (warm) |
|
_________________________________________________________________ |
| Above average |
3 |
15 |
5 |
| Average |
3 |
5 |
4 |
| Below average |
11 |
7 |
5 |
|
_________________________________________________________________ |
Main feature(s): 79% of springs 1945-1961 (warm
phase) had below average incidence of cyclonic days (i.e above average
anticyclonic days) while 56% of springs 1962-1988 (cold phase) had above average
incidence of cyclonic days.
In springs 1989 to 2002, 57% had average S indices, while
for both the P and C indices, roughly equal numbers of springs occurred in each
category confirming that there was no predominance of warm
weather types from 1989 to 2002 which would account for the
warmth of these recent springs.
This
chart compares
hours of sunshine in each spring 1961-2002
and shows that some springs from 1989 to 2002 were exceptionally sunny: 1990;
1995; and 1997. Another factor that may
have contributed to the unusually high temperatures of some of these springs is
dry soils which heat up more quickly on sunny days than wetter soils. For
example, dry soils were an important factor in the record high temperatures of
early August 1990 when a new UK high temperature record of 37.1 C at Cheltenham
was set. The presence of dry soils may be deduced from the Table below which
shows the percentage of average (1961-90) spring rainfall each year from 1989 to
2002 together with the mean spring CET anomaly (from 1961-90 average) and the percentage of average
(1961-90) spring sunshine. The following springs
would be expected to have drier than average soils as they had
well below
average spring rainfall: 1990; 1991; 1995; 1996; & 1997. However, both
1998 & 1999 which were very warm had neither above average sunshine nor below
average rainfall showing that these factors were not important in all the warm
springs.
| |
|
|
|
| |
|
|
|
| |
Mean spring |
% of average |
% of average |
| |
temperature anomaly C |
spring sunshine |
spring rainfall |
|
___________________________________________________________________ |
| 1989 |
0.73 |
116 |
97 |
| 1990 |
1.33 |
135 |
41 |
| 1991 |
0.57 |
87 |
79 |
| 1992 |
1.63 |
103 |
106 |
| 1993 |
0.90 |
92 |
107 |
| 1994 |
0.53 |
99 |
113 |
| 1995 |
0.47 |
124 |
71 |
| 1996 |
-0.93 |
87 |
74 |
| 1997 |
1.33 |
121 |
61 |
| 1998 |
1.27 |
94 |
126 |
| 1999 |
1.60 |
97 |
100 |
| 2000 |
0.87 |
104 |
136 |
| 2001 |
0.20 |
105 |
124 |
| 2002 |
1.2 |
113 |
91 |
|
___________________________________________________________________ |
Conclusion: very high sunshine totals and drier soil conditions may
have been important factors in the warmth of some of the springs
1989 to 2002 but not in others. The synoptic weather patterns were not similar
to those of an earlier period of warm springs 1945-1961 confirming that spring
weather types have warmed since 1989 and this chart
shows that this was part of a long term warming of
spring weather types since 1881. Whether or not this warming of spring weather
types is caused by higher concentrations of CO2 in the atmosphere is
debatable for the two following reasons:
1) the long term warming of weather types since 1881 was
interrupted from 1961 to 1987 while atmospheric
concentrations of CO2 were increasing throughout this period.
2) there was no warming of weather types in winter and
summer 1881 to 2002 which should not be the case if higher concentrations of CO2
in the atmosphere are driving temperatures upwards .
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