London scoping - ukcip

Final Report
54
Figure 4.7 Winter (December to February) precipitation anomalies (%) for the Eastern England
grid box of HadCM3 (grey) compared with a downscaled (red) scenario for Kew, both
from the Medium-High Emission scenario. The downscaled scenarios were produced
using the Statistical DownScaling Model (SDSM) forced by HadCM3 predictor
variables from the A2 experiment (http://www.sdsm.org.uk/). Anomalies were
calculated with respect to the 1961-1990 averages.
Precipitation anomaly (%)
100
50
-50
-100
4.6 Key Uncertainties
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1960 1980 2000 2020 2040 2060 2080 2100
Before the potential impacts of the UKCIP02 and SDSM climate changes for London are
discussed, it is imperative that the key uncertainties attached to the scenarios be identified:
Although the emissions used as the basis of the UKCIP02 scenarios represent the
full range reported by the IPCC (2001), the scenarios available herein for statistical
downscaling (just the Medium-High Emissions and Medium-Low Emissions
scenarios) represent a narrower range. It is also currently impossible to assign
probabilities to the various emission scenarios.
There are a large number of scientific uncertainties concerning the future behaviour
of emitted greenhouse gases, the significance of aerosols and soot particles,
carbon-cycle feedbacks and ocean responses to greenhouse gas forcing. Different
global and regional climate models will, therefore, produce different results
depending on the treatment of these factors. The HadCM3 model produces rainfall
changes close to the model range for winter, but simulates a larger reduction in
summer rain than most models. Such inter-model differences over the UK may be
expressed as uncertainty margins to be applied to the UKCIP02 scenarios of
change in temperature and precipitation (Table 4.8).