Page 13 - 全球气候变化及其影响Global Climate Change and Its Impacts-185×260

Chapter 1 Scientific Basis of Global Climate Change

IV. Role of Polar Regions

The polar regions, including the Arctic and Antarctic, are critical components of the
global climate system. The formation and melting of polar ice sheets and sea ice not only
directly affect local climates and ecosystems but also profoundly influence global climate
through complex feedback mechanisms. The unique geographical locations and environ-
mental conditions of the polar regions make them “amplifiers” or “buffers” of global climate
change, and their transformations hold significant implications for the stability and future
trajectory of the global climate system.
(1) Formation and Melting of Polar Ice Sheets and Sea Ice
Polar ice sheets are primarily concentrated in Antarctica and Greenland, forming mas-
sive ice bodies compressed from millennia of accumulated snowfall. The Antarctic ice sheet
is Earth’s largest freshwater reservoir, with a volume sufficient to raise global sea levels by
approximately 60 meters. The melting of the Greenland ice sheet could lead to a sea-level
rise of about 7 meters. Sea ice, formed by the freezing of seawater under low-temperature
conditions, is mainly distributed in the Arctic region. The extent and thickness of Arctic sea
ice play a pivotal role in global climate.
The formation and melting processes of polar ice sheets and sea ice are directly influ-
enced by global temperature changes. As global temperatures rise, the melting rates of polar
ice sheets and sea ice accelerate. According to observational data, the area of Arctic sea ice
has significantly decreased over the past few decades, with summer sea ice coverage shrink-
ing to historically low levels. The melting rate of the Antarctic ice sheet is also accelerating,
particularly in the western regions, where the disintegration of ice shelves and the accelerat-
ed flow of glaciers have led to large volumes of ice entering the ocean, thereby contributing
to sea level rise.
Sea level rise not only directly impacts coastal ecosystems and human livelihoods but
also alters global ocean circulation patterns. For example, the North Atlantic Current is a
critical factor influencing Europe’s climate, and the melting of polar ice sheets and sea ice
could disrupt this current through freshwater influx, thereby affecting climate patterns in Eu-
rope and North America.
(II) Ice-Albedo Feedback
The ice-albedo effect in polar regions is one of the critical feedback mechanisms influ-
encing global climate change. Albedo refers to a surface’s ability to reflect solar radiation,
and snow/ice-covered surfaces exhibit high albedo, reflecting most solar radiation and there-
by reducing heat absorption by the Earth’s surface. For example, Arctic sea ice has an albedo
of approximately 50%-70%, while exposed seawater has an albedo of only 10%-15%.
However, as global temperatures rise, the melting of polar ice sheets and sea ice reduc-
es snow/ice coverage, exposing lower-albedo ocean or land surfaces. These surfaces absorb
more solar radiation, further intensifying surface temperature increases and forming a pos-
itive feedback loop. This feedback mechanism, termed the “ice-albedo feedback,” is one of

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