During the MOSAiC expedition, a number of unusual factors were observed and investigated this winter. These included ice-drift and ice-thickness anomalies, which AWI experts surmised would likely have an effect on the summertime melting; model comparisons have since proven them right. And now there are a range of further factors that can contribute to the massive sea-ice retreat, the most rapid loss of ice cover ever recorded in the month of July: this year, temperatures on the East Siberian coast were more than 6 °C warmer than the long-term average in May and June. A cell of warm air over the region dominated the weather in the Arctic, leading to temperatures far above the long-term average. As a result, the snow melted early in the year, and Siberia’s permafrost soils began thawing. In June, this warming also led to intensified sea-ice retreat in the Laptev Sea, a phenomenon that spread to the East Siberian Sea in early July. By mid-July this had progressed to such an extent that the Northeast Passage was completely open for the first time in 2020. Since the beginning of July, conditions have changed: there is a high-pressure cell over the East Siberian and Chukchi Seas, accompanied by unusually warm temperatures (up to 10 degrees Celsius above average) over the Central Arctic. The stable atmospheric pressure system over the Arctic helped to strengthen the warm-air cell, which led to intensified melting of the snow cover on the ice, and with it, to an earlier breakup and melting of seasonal ice. Researchers consider areas in which less than 15 percent of the ocean is covered with ice as “ice-free”.