Climate Sense

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of the science. In most other fields the UKCIP02 results fall

close to the central estimate in the UKCP09 projections.

How the projections are delivered

Probabilistic projections are given at a resolution of 25

kilometres, but are also presented as averages over larger

land and marine regions. They are delivered over seven

overlapping 30-year periods and for three future emissions

scenarios. Variables covered include temperature, precipi-

tation, relative humidity, cloud cover, heat radiation and

mean sea level pressure. Monthly, seasonal and annual aver-

aged data are also provided.

There is a range of confidence within the climate projec-

tions. There is very high confidence in global warming

due to manmade greenhouse gas emissions, while only

moderate confidence in projections at a continental scale.

Information at a resolution of 25 kilometres is based on the

continental scale, but includes the influence of local condi-

tions such as mountains and coastline. However, adding

regional detail also adds uncertainty. Confidence is also

affected by the variable under discussion. For example, no

probability information is given for regional or local wind

changes.

What the projections tell us

The projections give a measure of the strength of evidence

for theUKclimate changing in a particularway–a projected

level of precipitation or temperature rise, for instance. The

probability depends on the weight of scientific evidence

behind the projections. It’s important to understand these

probabilities reflect how sure we are that a change will

happen, rather than the ‘percentage chance’ of it occurring.

projections. UKCIP02 overestimated the reductions in rainfall because its

model (HadCM3) has a tendency to dry out compared to other models.

The new projections better encompass the true range of our knowledge

Comparison of changes in summer average rainfall by the 2080s under high emissions scenarios,

from the UKCIP02 report and as projected in UKCP09

Source: Met Office UK

Maps of winter and summer temperature change for

2080s medium emissions compared with 1961-90

Source: Met Office UK

The 50 per cent probability level (where the evidence for being above or below this level is equally strong) gives a useful central estimate. The 10 per cent and

90 per cent probability levels give a useful range of possible outcomes