Arctic sea ice actually comprises most of the solid ground in the Arctic. For many Arctic inhabitants, it is thus literally the basis of their existence, but it is melting away beneath them. For scientists, Arctic sea ice is a pointer to how much the warming of the Earth is affecting polar regions. Each year, the extent of the sea ice area, which expands and shrinks during the year, is measured for this purpose. Also this year, the minimum extent was observed with satellite imagery in mid-September.
For years, the area of the minimum extent of Arctic sea ice has been declining. For this year, the minimum area value of about 4.79 million square kilometers was the tenth lowest since records began in 1979. This was despite the fact that long periods of heat had prevailed in large areas of Europe and in North America. Temperatures averaged 0.4°C above peak levels, reaching new highs. “This summer shows once again that sea ice cover is characterized by long-term trends and short-term, strong year-to-year variations caused by the influence of weather and ocean currents,” explains Professor Christian Haas of the Alfred Wegener Institute.
Although the minimum expansion fortunately did not set a new record this year, it follows the general trend that has been pointing downward for 16 now. “This year continues a sharp decline in sea ice coverage since the 1980s,” said Walt Meier, a sea ice researcher at the National Snow and Ice Data Center in Boulder, Colorado. “These are not random fluctuations or coincidences. It’s a fundamental change in ice cover in response to warming temperatures.” Overall, about 12 percent of sea ice area has disappeared per decade since satellite measurements began, research team have calculated.
Critics often cite individual regions where the sea ice area has not retreated further, but has actually increased. Also this year, some regions had been recorded where the ice had spread further south instead of retreating north. These included the east coast of Greenland and central and eastern areas in the Russian Arctic. This ice originally came from the central area of the Arctic and had drifted. Experts attribute this to the distribution of high and low pressure areas south of the Arctic Circle, which had prevented an exchange of air between the Arctic and the middle latitudes. Among other things, this had led to heat waves in central and southern Europe and cooler air masses in the north. Greenland, Iceland, and other Arctic regions had recorded more frequent cool temperatures and precipitation.
AWI also measures ice thickness each summer to learn more about the quality of Arctic sea ice. This is because animals that live on pack ice require a minimum thickness to live on the ice. This year, ice thickness was not greatly reduced, but again follows the downward trend of previous years. Such fluctuations overall are also often used by critics to deny the effects of warming. But for modelers, these fluctuations are a sign of the complexity of the “Arctic sea ice” system. Because despite all the knowledge gained by science in recent years and decades, new connections are always being discovered. “These fluctuations remain difficult to predict and require more extensive systematic and continuous observations as well as better climate models,” says Dr. Gunnar Spreen of the University of Bremen. And the satellites over the Arctic help keep an eye on the region.
Dr Michael Wenger, PolarJournal
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