Polar Regions
Polar regions include the Arctic in the Northern Hemisphere and Antarctica
in the Southern Hemisphere. The Arctic encompasses a large, mostly frozen ocean
surrounded by land, is home to almost four million people (
ACIA, 2004),
and includes some or all of the territories of eight nations, including the
United States. By contrast, Antarctica is an ice-covered continent surrounded
by ocean and is generally uninhabited.
The Arctic is expected to experience the greatest rates of warming compared
with other world regions (
IPCC, 2007a).
In part, this is because ice has greater reflectivity (also known as albedo)
than the ocean or land. Melting of highly reflective snow and ice reveals
darker land and ocean surfaces, increasing absorption of the sun's heat and
further warming the planet, especially in those regions. There is evidence that
climate change is already having observable impacts in the Arctic and in
Antarctica. Many of these observed changes are consistent with the expected
effects of climate change under a range of climate scenarios.
Effects
on the Climate System
- Average temperatures in the Arctic have risen at almost
twice the rate as temperatures in the rest of the world over the past few
decades.
- Widespread melting of glaciers and sea ice and rising
permafrost temperatures present additional evidence of strong Arctic
warming (see Figure 1).
- The above trends are expected to continue during this
century, resulting from ongoing increases in atmospheric concentrations of
greenhouse gases (though greenhouse gases do not primarily originate from
the Arctic).
- Melting of Arctic glaciers is a contributing factor to sea-level
rise around the world.
- Warming is very likely to alter the release and uptake
of greenhouse gases from soils, vegetation, and coastal oceans.
- Ocean
acidification will adversely affect marine
calcifiers by making it more difficult for these organisms to form
protective shells
- Reduction in sea ice is very likely to have devastating
consequences for polar bears, ice-dependent seals, and local people for
whom these animals are a primary food source.
Effects
on Biological and Human Systems
- Arctic impacts will have implications for biodiversity
around the world because migratory species depend on breeding and feeding
grounds in the Arctic.
- Reduced sea ice is likely to increase marine access to
the region’s resources, expanding opportunities for shipping and possibly
for offshore oil extraction (although operations could be hampered
initially by increasing movement of sea ice in some areas).
- As frozen ground thaws, many existing buildings, roads,
pipelines, airports, and industrial facilities are likely to be
destabilized.
- Increased areas of tree growth in the Arctic could
serve to take up carbon dioxide (CO2, the principal greenhouse gas emitted
by human activities) and supply more wood products and related employment,
providing local and global benefits. However, tree growth would mean
absorption of additional sunlight (as the land surface would become darker
and less reflective) and add to regional warming.
- Climate change is taking place within the context of
many other ongoing changes in the Arctic, including observed increases in
chemical contaminants entering the Arctic from other regions, overfishing,
land use changes that result in habitat destruction and fragmentation,
rapid growth in the human population, and cultural, governance and economic
changes.
The conclusions of the ACIA report
are further supported by evidence from remote sensing technologies. Satellites
and U.S. and British Navy submarines have provided data on retreating Arctic
sea ice and decreasing Arctic ice thickness. Satellite data show that the
extent of Arctic sea ice has decreased by about three percent per decade.
Figure 2 below shows trends in Arctic sea ice extent since the 1860s.
Upward-looking sonar data from U.S. Navy submarines between 1987 and 1997
show it is very likely that average ice thickness in the Arctic has decreased
by up to 1 meter (
IPCC,
2007a).
The Intergovernmental Panel on Climate Change (
IPCC 2007a
and 2007b) supports and extends the ACIA’s conclusions with additional
evidence. The IPCC notes that “the resilience shown historically by Arctic
Indigenous Peoples is now being severely tested,” with impacts on food
availability and personal safety that are changing hunting and traveling
practices. Community infrastructures will be harmed by the warming and thawing
of permafrost. A less severe climate may bring benefits as well, such as
reduced heating costs, new agricultural and forestry opportunities, and more
navigable northern sea routes, but such benefits will depend on local
conditions.
Antarctica
Like the Arctic in the Northern Hemisphere, Antarctica in the Southern
Hemisphere has been experiencing effects attributable to changes in regional
climate. Future changes resulting from global climate change are also expected
to be significant in this region of the world.
Over the past half-century, there has been a marked warming trend in the
Antarctic Peninsula. Much of the rest of Antarctica has cooled during the last
30 years, due to ozone depletion and other factors, but this trend is likely to
reverse. Surface waters of the Southern Ocean surrounding Antarctica have
warmed and become less saline, and precipitation in this region has increased (
IPCC, 2007a).
Antarctica has experienced significant retreat and collapse of ice shelves,
the result of regional warming. The loss of these ice shelves has few direct
impacts on sea level and global climate. Because the ice shelves were floating,
their melting does not directly add to sea level rise. They usually are
replaced by sea-ice cover, so overall
albedo
(reflectivity) changes very little (
IPCC, 2007a).
Satellite observations show no significant change in Antarctic sea-ice
extent over the 1973-2005 period. Analysis of whaling records and modeling
studies provide some evidence for longer-term declines in sea ice extent in
some regions, but there are not enough data to provide firm conclusions (
IPCC, 2007a).
As climate change continues, most of the land-based Antarctic ice sheet is
actually likely to thicken if projected warming increases snowfall. There is a
small risk, however, that the West Antarctic ice sheet will retreat in coming
centuries. This is because the West Antarctic ice sheet is moored in an oceanic
basin, where slippery mud covers the basin floor. This unique setting makes the
ice sheet potentially unstable (
IPCC, 2007a).
References
