In the winter of 2020, an unusual wind pattern pushed old Arctic sea ice into perilous territory. Large swaths of the Arctic’s diminishing store of old ice are now at risk of melting due to warming waters. But why is old ice so important, and how did this happen?
When the Arctic Ocean is blanketed in darkness during the winter, temperatures plummet to below -30 degrees Celsius. As the seawater below freezes, existing floating ice thickens, and the ice advances into previously open water areas. The ice thins and retreats in the summer, when temperatures rise and the sun shines for months at a time.
Scientists wait for the annual minimum coverage of Arctic sea ice in September, a useful indicator of how quickly the region is changing. The ice that survives the summer melt season can be used again the following winter. Some ice can last for several summers before melting. This is especially true in the colder areas near the North Pole.
Perennial ice is ice that has survived the summer and has become thicker, rougher, and more resilient as a result of its ordeal. It’s an important part of the Arctic’s climate and ecology, and now at a risk of melting due to warming of waters.
Perennial ice is especially valuable because it can survive the summer, shielding the Arctic Ocean from the sun and keeping the region cool. Every year, however, the ice melt season gets longer and the growth season gets shorter. In the Arctic, both seasons are becoming hotter. These factors conspire against perennial ice, resulting in less ice surviving each year’s melt season.
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