Current warming and likely future impacts - Climate Change: Biological and Human Aspects - page 316

it is likely that there has been a significant influence from human activity on the recent
warming.
The 2009 UKCIP report was branded as UKCP09 (not UKCIP09 as had been
expected prior to 2008) and had the full title of UK Climate Projections (Jenkins
et al., 2009). Its scenario forecasts were only slightly different to those given by
UKCIP02. (The model resolution for UKCIP02 was 50 km 2 whereas for UKCP09
it was 25 km 2 .) It gave a range of probabilities: 10, 50 and 90%, with the middle
50% being the most likely (the mean values) and the 10 and 90% probabilities being
the high and low extremes (the two tails to the binomial bell-shaped probability
distribution) that were thought possible but only with low probability. The principal
scenario forecast differences between UKCIP02 and UKCP09 were as follows.

In the case of mean temperature, projected changes in UKCP09 for were generally
somewhat greater than those in UKCIP02.
In the case of the summer reduction in rainfall, the UKCP09 prediction was not
as great as that projected in UKCIP02. UKCP09 had UK annual rainfall in the
2080s largely unchanged compared to the beginning of the century but with central
England and most of East Anglia receiving slightly less rain and the rest of the UK
slightly more rain across the year.
The overall outcome under the medium emissions scenario (equivalent to IPCC
scenario A1B) was that all areas of the UK will become warmer, more so in
summer than in winter. Changes in summer mean temperatures are greatest in
parts of southern England (up to 4.2 ◦ C; 2.2-6.8 ◦ C) and least in the Scottish islands
(just over 2.5 ◦ C; 1.2-4.1 ◦ C).

The key scenario forecast points are outlined below.

Mean daily maximum temperatures will increase everywhere. The summer average
will increase by 5.4 ◦ C (2.2-9.5 ◦ C) in parts of southern England and 2.8 ◦ C (1-5 ◦ C)
in parts of northern Britain. Increases in winter will be 1.5 ◦ C (0.7-2.7 ◦ C) to 2.5 ◦ C
(1.3-4.4 ◦ C) across the country.

2.4 ◦ C( 6.8 ◦ C) to

Changes in the warmest day of summer will range from + − 2.4 to +

4.8 ◦ C( 12.3 ◦ C), depending on location, but with no simple geographical

+ + 0.2 to +

pattern.

The biggest changes in precipitation in winter, increases up to 33% (9 70%), will

be seen along the western side of the UK. Decreases of a few per cent (

−

− 11 to

+ 7%) will be seen over parts of the Scottish highlands.

The biggest changes in precipitation in summer, down to about − 40% ( − 65 to

− 6%), will be seen in parts of the far south of England. Changes close to zero ( − 8

to + 10%) will be seen over parts of northern Scotland.

However, we must bear in mind that water demand in the summer is higher than that
in the winter and that the bulk of the UK's population lives in the southern half of
England and Wales, and that the above refers to future change whereas currently the
east and south east of England have lower rainfall that the west and north of Great
Britain. So water shortages in the south east of England are a concern. For a summary
overview of the temperature and precipitation changes anticipated by the 2009 report
see Figure 6.8.