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warming of around 4 C is predicted for high latitudes of the northern hemisphere in
summer. The larger land area in the northern hemisphere leads to a stronger
response to the radiative forcing than in the southern hemisphere. Additionally,
the decrease in summer sea-ice cover amplifies the summer warming. In contrast,
minimum warming is predicted in the Southern ocean due to strong ocean heat
uptake in this region. In addition to this global scale pattern, some regional scale
patterns in the temperature changes become visible. As most climate models predict
a reduction in the thermohaline circulation as a response to the increasing green-
house gas concentration, the heat transport from the tropics to the Polar regions will
be affected in the northern hemisphere (Schmittner et al. 2005 ). This will result in a
local cooling in the Labrador Sea in winter and a reduced warming in summer
according to the model simulations (Fig. 18.3 ).
The simulated future changes in sea surface temperatures shown in Fig. 18.3 will
result in a general poleward movement of biogeographical regions (see Sect. 18.2 )
until the end of the twentieth century. The extent of the present-day biogeographical
regions and the resulting future changes are shown in Figs. 18.1 and 18.2 .This
projection is based on the location of modeled mean winter and summer sea surface
isotherms for the end of the twentieth century (M
uller et al. 2009 , Appendix Figs. 1
and 2) characteristic for the current boundaries of the respective regions (see
Table 18.1 , Figs. 18.1a and 18.2a ). Despite the proven recent regional warming in
the western Antarctic Peninsula (Vaughan et al. 2003 ) there will be almost no
changes in the northern delimitation of the Antarctic region until the end of this
century based on our model. The Arctic region, in contrast, will shrink considerably
at its southern border, especially due to warmer winter temperatures while new ice-
free coastal Arctic habitats will become available in the north following the
retreating pack-ice border (1 C August isotherm) in summer (Fig. 18.2b ;M
uller
et al. 2009 ). The current cold-temperate regions of both hemispheres will become
compressed as the warm-temperate regions are shifting polewards. The cold-
temperate regions will gain much new area at the expense of the Polar region only
in the N-Atlantic while in the S-Atlantic only the small sub-Antarctic islands will
become cold-temperate. The poleward expansion of the warm-temperate regions at
the expense of the cold-temperate regions is especially evident in western and
eastern S-America, in southeastern Australia and New Zealand, western N-America,
and along the European coastline. The warm-temperate regions themselves will lose
habitats at the expense of the projected widening of the tropical regions (Figs. 18.1
and 18.2 ). Recently, it was shown that this process has already started and five
different types of climatological measurements revealed a widening of the tropical
region of several degrees latitude since 1979 (Seidel et al. 2008 ). According to our
results, this future widening will be especially pronounced along the west and east
coast of S-America, along the northern and eastern coastlines of S-Africa and
Australia, in SE-Asia, W-Africa, and the Gulf of Mexico (Figs. 18.1 and 18.2 ).
It becomes apparent that the location of the boundary isotherms characterizing
present-day biogeographical regions (Table 18.1 ) will not move polewards at the
same pace according to the model simulations (Figs. 18.1 and 18.2 ). Thereby, the
annual mean temperature minima and maxima and the resulting temperature gradi-
ent will change along vast coastlines compared to present day. As a consequence,
some biogeographical regions will not be extended or reduced as a whole
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