Following two months of record heat and precipitation in fall 2022, an estimated 7,500 lakes in West Greenland turned brown, began emitting carbon and decreased in water quality in less than a year. The spike in temperatures caused the precipitation to fall as rain instead of snow. The heat also caused permafrost to thaw, releasing an abundance of carbon, iron, magnesium and other elements that the rain washed into the lakes. Researchers found a decrease in phytoplankton that absorb carbon dioxide from the atmosphere through photosynthesis within the lakes, and an increase in plankton that break down and release carbon. Instead of sequestering carbon dioxide in the summer, the lakes have become a source of it, with a 350% increase in the flux of this greenhouse gas from them.

West Greenland is home to tens of thousands of blue lakes that provide residents with drinking water and sequester carbon from the atmosphere. Yet after two months of record heat and precipitation in ...