Energy > Climate Change
Arctic sea ice is disappearing
This article is part of our series focused on the causes and consequences of a warming planet.
Sea ice is frozen seawater that forms, grows and subsequently melts in the ocean. It forms on the ocean’s surface when the ocean surface temperature is below freezing.
Sea ice covers about 12% of the ocean’s surface. However, the extent of sea ice varies greatly during the year, thawing and shrinking during the summer and freezing and expanding during the winter.
Sea ice is important because it keeps the polar-regions cool and helps moderate the Earth’s climate. However, both the thickness and extent of Arctic sea-ice has declined dramatically over the past thirty years. This loss of sea ice has the potential to accelerate global warming and change the climate.
The reduction in sea ice is caused by more of the sea ice melting during the summer than is freezing during the winter. As the sea ice oscillates between summer melting and winter freezing, the size of the Arctic ice sheet declines over a period of years and decades.
This decline over time is driven by the difference in the impact of sunlight shining on ice versus shining on water. When sunlight shines on sea ice, most of the light is reflected back into space and little is absorbed by the ice as heat. But when sunlight shines on the water of the ocean surface, most of the light is absorbed by the water as heat and little is reflected back into space.
This phenomenon can cause what is called a "feedback loop" where the area of sea ice gradually decreases over a period of years. As sea ice melts, it exposes open water to the sun. So more water and less ice creates more heat. The additional heat melts more sea ice, which exposes more water to the sun. So more heat is accumulated in sea water. The additional heat melts more ice which exposes more water and so on.
This feedback loop is triggered initially by human-caused warming of the Arctic. But once triggered, the feedback loop drives the long-term loss of Arctic sea ice regardless of what we do to control the Arctic warming.
Antarctica also has sea ice. The extent of Antarctica’s sea ice is much less than that of the Arctic because most of Antarctica’s ice sheet is land ice that covers the huge continent of Antarctica.
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Don Hofstrand, retired extension agricultural business specialist, firstname.lastname@example.org
Reviewed by Dr. Eugene Takle, retired professor emeritus Iowa State University