Denmark faces surge in marine heatwaves as ocean temperatures rise

New data from the Danish Meteorological Institute (DMI) and analysis from the think tank Tænketanken Hav indicate a significant increase in marine heatwaves within Danish waters. DMI’s Climate Atlas predicts that in a medium-emission scenario, the number of days with marine heatwaves could reach 190 days per year between 2041 and 2070, a 430 percent increase compared to the 1981-2010 reference period. By the end of the century, this could rise to 250 days per year.

Since the 1980s, the number of marine heatwave days has already increased by more than 170 percent. In 2025 alone, 130 days of marine heatwaves were recorded in Danish waters. The most dramatic increases have been observed in the Baltic Sea near Bornholm, which saw a 320 percent rise, and the Belt Sea, which saw a 209 percent increase.

These rising temperatures are exacerbating oxygen depletion and placing severe pressure on vulnerable marine species such as cod and herring. Experts emphasize the need for more ambitious and climate-robust ocean policies to address these environmental shifts.