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Figure 18.3.
Source: Figure 11.11 of IPCC-AR4 (2007), Chapter 11 of Working Group 1.
winter over elevated areas due to snow-albedo feedback. This feedback
effect is poorly modeled by AOGCMs due to their insuffi cient horizontal
resolution to resolve the rapidly varying and rising topographic nature of
the mountains.
Figure 18.4 shows seasonal variation in the temperature and
precipitation changes averaged over 21 climate models driven by the A1B
emission scenario. Change is from the periods 1980-1999 to 2080-2099.
The top and middle rows show temperature and precipitation changes
for annual, winter (DJF—December, January, February) and summer (JJA
—June, July, August). The bottom row shows the number of models out of
21 that projected precipitation increases. As indicated in the fi gure, there is
less seasonal variation in the temperature increases along the west coastal
regions of North America, due to the infl uence of the oceans.
Climate scientists usually have a higher confi dence in projecting changes
in temperature than in other meteorological variables like precipitation.
However, in the context of climate change, changes in temperature and
precipitation constitute the most important impact on our environment,
including socio-economic systems. The second row in Fig. 18.4 shows the
seasonal variation in the precipitation change projected by the models.
With the displacement of the westerlies northward, in conjunction
with the intensifi cation of the Aleutian Low over the Gulf of Alaska,
the climate models project a relatively large percentage increase in the
winter precipitation over the northern high-latitude regions, including the
Canadian Rockies in Yukon and northern British Columbia (IPCC-AR4,
WG-1 2007). This fractional increase is enhanced on the western windward
slopes of the Rockies (as an orographic precipitation). As indicated in
the fi gure, the summer season shows a relative decrease in precipitation
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