Impacts and Issues
Both polar regions serve as heat sinks, that is, areas where more energy
is radiated away from Earth than is absorbed. However, because the
arrangement of land and sea at the two poles is so different—almost
reversed—the two areas play distinct roles in global climate.
Because of the symmetrical arrangement of land and sea in the south
polar region, water and air flow in well-defined circular patterns around
Antarctica. This circumpolar vortex tends to isolate the interior of the
continent from the atmospheric circulations of the rest of the world.
Thus, most of the ice in Antarctica shows no signs of melting any time
soon, and may even gain mass from increased snowfall. However, the
West
Antarctic Peninsula
is not isolated by the circumpolar flow pattern
and has warmed by about 5.4°F (3°C) over the last half century. As a
result, 87% of the glaciers on the peninsula (about 300 of them)
accelerated their flow to the sea by an average of 12% from 1993 to
2003, contributing to accelerating sea-level rise; further acceleration
may have occurred since 2003.
In 2002, because of regional climate changes that have been traced to
global climate change, the floating coastal Larsen B ice shelf (1,253
square mi, or 3,245 square km in area) collapsed unexpectedly in just
one month. The breakup of the floating ice did not raise sea levels
directly, but has allowed some glaciers on the West Antarctic Peninsula
to accelerate further, which does raise sea levels.
The ice covering the
North Pole
, in contrast to that covering
the South
,
can have no direct effect on sea level because it is already floating.
However, it reflects most of the light that falls on it into space, keeping
the north polar region (and thus Earth) cooler than it would be
otherwise. It is fragile compared to Antarctica's ice or that of Greenland,
being only a few meters thick and floating on water.
In 2007, unprecedented summer melting of the Arctic sea-ice cap was
observed, with open water stretching from the Pacific to the Atlantic
along the northern coast of
North America
for the first time in recorded
history. Open sea absorbs more
solar energy
than ice, so the more the
Arctic sea ice melts, the warmer the Arctic gets. Further, in 2006,
measurements of the changing gravitational pull of ice in Greenland
verified that the mass of the ice sheet is decreasing as glaciers (so far,
mostly around the southern coasts) accelerate their flow to the North
Atlantic. The freshwater from the glaciers may slow the overturning
thermohaline circulation of the
Atlantic Ocean
, with effects on climate
throughout the Northern Hemisphere.
Warming is already having other effects on the Arctic region. Melting of
permafrost and speeded coastal erosion are damaging human settlements
and forcing some villagers to flee to higher or more stable ground.
Warmer conditions are causing shrubs and forests to spread forward and
snow cover to form later in the fall, melt earlier in the spring, and cover
less territory, all of which causes the land to be darker on average and to
absorb more heat, speeding warming. Anaerobic
decay of organic matter
in melting permafrost may, in decades to come, release millions or
billions of tons of methane, a potent greenhouse gas, further speeding
global climate change. No other large ecosystem has been as severely
impacted, as yet, as the Arctic. The West Antarctic Peninsula, although
seeing dramatic warming, is almost devoid of life.
Do'stlaringiz bilan baham: |