London scoping - ukcip

Final Report
55
Table 4.8 Suggested uncertainty margins to be applied to the UKCIP02 scenarios of changes in
average winter and summer temperature and precipitation
Average Temperature
Winter (ºC)
Summer (ºC)
Average Precipitation
Winter (%)
Summer (%)
Low Emissions Medium-Low
Emissions
±0.5
±0.5
±5
+10
±1.0
±1.0
±10
+15
Medium-High
Emissions
±1.5
±1.5
High Emissions
Note: all summer rainfall sensitivities are positive because UKCIP02 summer rainfall changes are already
considered to be at the drier end of the inter-model range.
Source: Hulme et al. (2002).
The realism of the UKCIP02 and SDSM scenarios ultimately depend on the
realism of the HadCM3 model output from which both are derived. Fortunately,
the performance of this model, when assessed using a range of pattern correlation
techniques, is consistently amongst the world’s best for the current climate (Wigley
and Santer, pers. comm.).
There is little agreement amongst different models about regional patterns of sealevel
rise. This is because of regional variations in the warming of ocean water
(and associated thermal expansion), ocean circulation and atmospheric pressure. In
UKCIP02, future changes in mean sea level were derived using local rates of
natural land movement (subsidence) together with the full range of UKCIP02
global sea level rise for the three future periods. This idealised approach does not
include any variations in regional sea level rise due to changing estuary shape,
sediment consolidation or wave heights, so an uncertainty margin of ±50% is
attached to each scenario of sea level rise in Table 4.5 and 4.6.
Most climate models, including HadCM3, suggest a weakening (but not a shutdown)
of the north Atlantic Gulf Stream over the next 100 years. However,
changes in the salinity and temperature profile of north Atlantic surface waters,
could in theory lead to a shut-down of the Gulf Stream. Although a cooling of UK
climate over the next 100 years because of a shut-down of the Gulf Stream is
considered unlikely, it can not be completely ruled out.
These factors should be borne in mind when considering the following set of climate change
impacts for London.
±15
+30
±2.0
±2.0
±20
+40