THE LAPTEV SEA, nestled between the north coast of Siberia and Russia’s New Siberian Islands, is known as the birthplace of ice. Every year, ice forms along its coasts in the autumn before being pushed west across the Arctic Ocean to Greenland and Norway’s Svalbard archipelago, where it breaks up come spring. Every year, that is, until this one. For the first time since records began, the Laptev Sea has not begun to freeze by late October (see chart). This is only the latest example of how climate change is rapidly transforming the Arctic. Scientists worry that it could have damaging knock-on effects across the region.

The delayed freeze is the result of an unprecedented heatwave in Siberia in the first half of the year. The record high temperatures, in addition to fuelling an outbreak of Arctic wildfires that have burned an area the size of Greece, have warmed ocean waters by more than 5°C. That heat has not yet dissipated, preventing the Laptev Sea from freezing on schedule. The peculiar weather is no coincidence. According to the World Weather Attribution project, a team of scientists that analyses possible links between climate change and extreme weather events, Siberia’s scorching temperatures would not have been possible without climate change. Changes to Atlantic currents, also the result of climate change, may also be contributing to the lack of ice.

The Laptev Sea’s woes are part of a broader transformation in the region. In the last four decades, the amount of so-called multi-year ice—sea ice that survives the warmer months—in the Arctic has been reduced by a half. Scientists expect that soon there may be none at all. What is happening in the Laptev Sea is a grim foreshadowing of this. In the 1980s, multi-year ice covered two-thirds of the sea; these days ice can be absent for months at a time. This causes ocean temperatures to rise further, as open water retains more heat than ice. It also plays havoc with the Arctic’s delicate ecosystem and is likely to threaten Arctic plankton, which play an important role in absorbing carbon dioxide. The open water of the Laptev Sea is another warning of the consequences of a fast-warming world.