The Antarctic is something of an anomaly in climate science. Unlike the Arctic, where the extent of summer sea ice has shrunk severely in recent years, the Antarctic has seen an average annual growth in sea ice of some 15,000 square km. And unlike its northern counterpart, for which a fall in sea ice has been largely consistent with climate-model predictions, the Antarctic’s behaviour has confounded climate modellers who have attempted to explain it.

The discrepancy is a big problem, because the extent of sea ice alters the region’s albedo. That affects how much solar radiation is reflected back out of the atmosphere, which in turn affects warming. According to Chang-Qing Ke and Zhu-De Shao at Nanjing University, however, there has been a lack of studies to evaluate precisely how much the Antarctic’s albedo has been changing relative to the Arctic’s. Mostly the parameter has been measured from ships and at research stations, but these have not been able to provide long-term data over a large scale.

Instead, Ke and Shao took their data from a first-release albedo product supplied by the Satellite Application Facility on Climate Monitoring, a collaboration between the meteorological services of various European countries. The researchers analysed the data by dividing it up into areas, setting a threshold for the presence of sea ice, and correlating values of albedo with sea ice and temperature.

In the Bellingshausen–Amundsen Sea sector of the Antarctic, the albedo dropped by more than 1.6% per decade between the years 1982 and 2009, the pair found. In three other regions, the Weddell Sea, Indian Ocean and Pacific Ocean sectors, however, the albedo rose between around 0.4 and 2.6% over the same time period. The Ross Sea sector saw almost no change in albedo. On average over all of the regions, the albedo rose by about 0.3% over the 28 years, and correlated with a rise in sea-ice concentration.

Ke says that he and Shao are not surprised by the results, and agree that they reinforce the current picture of an anomalous Antarctic. "The Antarctic climate is very complex," he added. "Sea ice, [the Pacific climate phenomenon] El Niño, ocean currents, solar radiation and wind are all factors that strongly affect it. At present, there is no uniform conclusion about the mechanism of Antarctic climate change. More research is needed on the Antarctic climate, and it is an important research direction."

Ke believes that he and Shao’s work will help others to understand what is going on in the Antarctic, currently at least. "Next, we will study the impact of Antarctic sea ice on the climate," he said. "The big difficulty in this [type of] study is that the Antarctic climate is very complicated. The work will take a long time."

The study is published in Environmental Research Letters (ERL).

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