Sea ice is simply frozen ocean water. It forms, grows, and melts in the ocean. In contrast, icebergs, glaciers, ice sheets, and ice shelves all originate on land. Sea ice occurs in both the Arctic and Antarctic. According to NSIDC (National Snow and Ice Data Center), on average, sea ice covers about 25 million square km of the Earth, or about two-and-a-half times the area of Canada. Although sea ice may not directly affect most people, it is a critical component of the planet because it influences climate, wildlife, and people who live in the Arctic.
Sea ice has a bright surface, so much of the sunlight that strikes it, is reflected back into space. As a result, areas covered by sea ice don't absorb much solar energy, so temperatures in the Polar Regions remain relatively cool. As gradually warming temperatures melt sea ice over time, fewer bright surfaces are available to reflect sunlight back into space, causing more solar energy to get absorbed at the surface, and raising temperatures further. This chain of events starts a cycle of warming and melting. The cycle is temporarily halted when the dark days of the polar winter return but starts again in the following spring. Even a small increase in temperature can lead to greater warming over time, making the polar regions the most sensitive areas to climate change on Earth.
The Sea Ice Index provides a quick look at Arctic and Antarctic wide changes in sea ice. It is a source for consistent, up-to-date data on sea ice extent (ocean area where there is at least 15% sea ice coverage). The Arctic sea ice extent averaged for February 2021 was 14.39 million square km, placing it seventh lowest in the satellite record for the month over recorded history. In February 2021, sea ice grew by an average of 9,900 square km per day; roughly half the average rate over the period 1981 to 2010 of 20,300 square km.
Antarctica has been losing about 134 billion metric tons of ice per year since 2002. This rate could speed up if the burning of fossil fuels continues at the current pace, causing sea levels to rise by several meters over the next 50 to 150 years.
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