The extent of sea ice blanketing the Arctic this winter fell to the lowest level on record, researchers announced this week, an ominous signal about the effects of climate change in the world’s fastest-warming region.

Arctic winter ice typically reaches its broadest expanse in March, after which it begins a slow melt over the spring and summer months, shrinking to its smallest area, or minimum extent, in September. The previous record winter low occurred in 2017.