Global Warming

Antarctica's sea ice reaches its lowest level since records began

The amount of sea ice surrounding Antarctica has reached its lowest level since modern records began, for the second year in a row.

Sea ice is frozen seawater that floats on the ocean's surface around the planet's polar regions. It forms at much lower sustained temperatures than freshwater ice does, at around 28.8 degrees Fahrenheit (minus 1.8 degrees Celsius). Sea ice builds up during the winter until it reaches its maximum extent, and then melts away in the spring and summer until it reaches its minimum extent.

In Antarctica, where summer and winter are flipped relative to the Northern Hemisphere, sea ice normally reaches its maximum extent in September, when sea ice covers around 7 million square miles (18.5 million square kilometers). At its minimum extent, at the end of February, historically only around 1 million square miles (2.5 million square km) remains.

Last year, the minimum sea ice extent was less than 772,000 square miles (2 million square km), the lowest total since scientists began recording sea ice extent with satellites in 1979. On Feb. 21 this year, that number had shrunk to just 691,000 square miles (1.8 million square km), which is roughly 40% less than the average between 1981 and 2010