The Arctic sea ice diminishes every year more and more. In 2012, it had reached a sad negative record with its extension of 3.4 million square kilometers. This year, the extension reached its second lowest value with 4.1 million square kilometers which is even less than the previous record in 2007. And according to experts from the Alfred-Wegener-Institute, who had been responsible for the measurements, the trend will continue.
Every September, researchers take stock. The melting season in the Arctic reaches its end, the size of the sea ice, the September minimum, is an important factor for climate change. “In the winter 2015/16, the air over the Arctic Ocean was largely more than 6°C warmer than on the average,” says Lars Kaleschke, sea ice physicist at the Center for Earth System Research and Sustainability at the University of Hamburg. “Through higher temperatures, the ice will grow less in winter.” But the researchers also looked at ice thickness. Aerial high-resolution pictures in various Arctic regions show: “Especially the newly built first-year ice was very thin this year, not more than one meter. Normally it is twice as much”, says Christian Haas. “The multi-year ice, on the other hand, was as thick as in previous years, around 3 -4 meters. This has delayed the ice loss in June and July, before it finally melted in August due to strong winds.” For a continuous assessment of ice thickness, the University of Hamburg and the AWI developed a new data product. For the first time, it combines measurements of the two ESA satellites CryoSat and SMOS and can thus provide trend data. “We were able to see a reduction of 10 centimeters in ice thickness at the end of the winter in comparison to previous years, a significant loss”, explains Lars Kaleschke.
The actual sea ice area is estimated by using satellite pictures. The team of Lars Kaleschke developed a better assessment to picture areas down to three kilometers. Until recently, only pictures with down to 12 kilometers resolution had been used. The visualizations allow the detection of details like gyres, channels and ice edges and thus indicate ice dynamics and therefore its stability. This lead to the detection of the Beaufort gyre, north of Alaska, breaking up the ice earlier than usual, namely in April. In May and June, the ice surface really was smaller than ever recorded before. Also unusual were large leads in the ice close to the North Pole.
Since August 2016, both North East and North West Passage are entirely open. The southern route through the North West Passage was thus navigable for yachts and a large passenger cruise ship. Only in 2008 both waterways were open at the same time. Arctic sea ice is considered a crucial element for the climate and a early warning system for global warming. In the 1970s and 1980s, the average summer minimum extensions were somewhere at 7 million square kilometers. “The retreat of Arctic sea ice is a clear sign for an unchecked global warming”, says Lars Kaleschke at the end.