Are Sea Ice levels really declining?

It is well known that global warming is affecting the poles dramatically. However, while sea ice extent at the North Pole has reached record lows, the coverage has been increasing in the South.

A recent study carried out by NASA and the British Antarctic Survey has been able to explain the sea ice drift in the Antarctic that has occurred over the last 20 years. They have found evidence to prove that changing winds have caused sea ice cover in the Antarctic to increase, despite the effects of climate change, which was published in ‘Nature Geoscience’. Maps created by the ‘Jet Propulsion Laboratory’ at NASA, which used more than five million daily ice motion measurements recorded for 19 years, have shown the changes in sea ice drift, which, until now, were unproven. Before this, the drift was merely hypothesised with the use of models of Antarctic winds but now this theory has a substantiated basis.

The growth of sea-ice cover is not spread evenly, with certain areas undergoing greater gains or losses. The diagram shows where growth is fastest, with the red areas in the northern and south-western parts of the continent experiencing the fastest rates. However, the blue regions in the north-west and north-east have been experiencing a decline, the area with the most rapid of shrinking is around the Antarctic Peninsula. This shows that the trends are not widespread and that the change of ice sheets is controlled by local changes in the winds. The winds affect the ice coverage by the air temperature as well as ice drift. Generally, the sea ice is blown away from the continent as a result of powerful northwards wind and since 1992, the spread of ice has doubled in areas but decreased hugely in others.

Globally, this sea ice spread is important because it reflects the sun’s heat as well as creating habitats for marine organisms. For obvious reasons, sea ice cover is thinner and less spread, but during the winter it grows and insulates the ocean from the freezing winter temperatures, allowing marine life to survive.

The growth of sea ice in the Antarctic is a stark contrast to the rapid decline of the Arctic, where the ice has reached record lows this summer. On September 16th 2012, seasonal melt meant the sea ice receded to 3.41 million square kilometres, the lowest seasonal minimum since satellite records began in in 1979. These surpass the previously smallest levels from 2007 by 760,000 square kilometres, 18% lower.

It is thought that this was caused by increasing levels of seasonal ice which forms over the winter, as it is thinner and gets broken up a lot easier than permanent ice. This causes a positive feedback loop to develop in which melt is quickened by increasing levels of seasonal ice, leading to more ice melt and so on. This year was also made worse by a large Arctic storm which caused this very thin ice to be completely destroyed.

While this melt is seasonal and the sea ice will refreeze at rates of up to 100,000 square kilometres a day, these levels of melt cannot be ignored. The levels of melt will probably grow in severity of the coming years due to global warming and it is expected that the Arctic will be ice free during the summer within 20 years.

It is important to point out that this does not disprove climate change, as the Antarctic Peninsula has shown the same warming as the rest of the Southern Hemisphere. While the sea ice expands, glacial ice is decreasing rapidly. As interesting as the expansion of sea ice is, it is important that these do not blur anybody’s views on climate change; the melt at the North Pole should be evidence enough.

Contributed by James Axton

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