|
5.7. Polar Regions
Climate change in the polar region is expected to be among the greatest
of any region on Earth. Twentieth century data for the Arctic show a warming
trend of as much as 5°C over extensive land areas (very high confidence),
while precipitation has increased (low confidence). There are some areas
of cooling in eastern Canada. The extent of sea ice has decreased by 2.9% per
decade, and it has thinned over the 1978-1996 period (high confidence). There
has been a statistically significant decrease in spring snow extent over Eurasia
since 1915 (high confidence). The area underlain by permafrost has been reduced
and has warmed (very high confidence). The layer of seasonally thawed ground
above permafrost has thickened in some areas, and new areas of extensive permafrost
thawing have developed. In the Antarctic, a marked warming trend is evident
in the Antarctic Peninsula, with spectacular loss of ice shelves (high confidence).
The extent of higher terrestrial vegetation on the Antarctic Peninsula is increasing
(very high confidence). Elsewhere, warming is less definitive. There has been
no significant change in the Antarctic sea ice since 1973, although it apparently
retreated by more than 3° of latitude between the mid-1950s and the early
1970s (medium confidence). [16.1.3.2.]
The Arctic is extremely vulnerable to climate change, and major physical,
ecological, and economic impacts are expected to appear rapidly. A variety
of feedback mechanisms will cause an amplified response, with consequent impacts
on other systems and people. There will be different species compositions on
land and sea, poleward shifts in species assemblages, and severe disruptions
for communities of people who lead traditional lifestyles. In developed areas
of the Arctic and where the permafrost is ice-rich, special attention will be
required to mitigate the detrimental impacts of thawing, such as severe damage
to buildings and transport infrastructure (very high confidence). There
also will be beneficial consequences of climatic warming, such as reduced demand
for heating energy. Substantial loss of sea ice in the Arctic Ocean will be
favorable for opening of Arctic sea routes and ecotourism, which may have large
implications for trade and for local communities. [16.2.5.3,
16.2.7.1, 16.2.8.1,
16.2.8.2]
In the Antarctic, projected climate change will generate impacts that will
be realized slowly (high confidence). Because the impacts will occur over
a long period, however, they will continue long after GHG emissions have stabilized.
For example, there will be slow but steady impacts on ice sheets and circulation
patterns of the global ocean, which will be irreversible for many centuries
into the future and will cause changes elsewhere in the world, including a rise
of sea level. Further substantial loss of ice shelves is expected around the
Antarctic Peninsula. Warmer temperatures and reduced sea-ice extent are likely
to produce long-term changes in the physical oceanography and ecology of the
Southern Ocean, with intensified biological activity and increased growth rates
of fish. [16.2.3.4, 16.2.4.2]
Polar regions contain important drivers of climate change. The Southern
Ocean's uptake of carbon is projected to reduce substantially as a result of
complex physical and biological processes. GHG emissions from tundra caused
by changes in water content, decomposition of exposed peat, and thawing of permafrost
are expected to increase. Reductions in the extent of highly reflective snow
and ice will magnify warming (very high confidence). Freshening of waters from
increased Arctic runoff and increased rainfall, melt of Antarctic ice shelves,
and reduced sea-ice formation will slow the thermohaline circulations of the
North Atlantic and Southern Oceans and reduce the ventilation of deep ocean
waters. [16.3.1]
Adaptation to climate change will occur in natural polar ecosystems, mainly
through migration and changing mixes of species. Some species may become
threatened (e.g., walrus, seals, and polar bears), whereas others may flourish
(e.g., caribou and fish). Although such changes may be disruptive to many local
ecological systems and particular species, the possibility remains that predicted
climate change eventually may increase the overall productivity of natural systems
in polar regions. [16.3.2]
For indigenous communities who follow traditional lifestyles, opportunities
for adaptation to climate change are limited (very high confidence). Changes
in sea ice, seasonality of snow, habitat, and diversity of food species will
affect hunting and gathering practices and could threaten longstanding traditions
and ways of life. Technologically developed communities are likely to adapt
quite readily to climate change by adopting altered modes of transport and by
increased investment to take advantage of new commercial and trade opportunities.
[16.3.2]
|