North Sea and Baltic Sea far too warm, with Helgoland especially affected

The heatwave did not stop at Germany’s shores. During June, July and August, surface temperatures in the North Sea and Baltic Sea climbed far above their long-term averages, according to an assessment by the German Maritime and Hydrographic Agency, or BSH.

The North Sea averaged 15.6 degrees Celsius, almost one degree above normal, making it the fifth-warmest summer there since 1997. The Baltic Sea reached an average surface temperature of 17.2 degrees, also nearly one degree above the long-term average and the seventh-warmest summer in the same period.

The German and Polish coasts, Sweden’s eastern coast and the far north were especially affected. June stood out, with temperatures almost three degrees above the long-term average. Helgoland recorded 66 days of marine heatwaves, while new records were measured in parts of the southern North Sea.

“These new highs in the southern North Sea and the 66 days with marine heatwaves off Helgoland show that extreme heat events are clearly affecting our home seas,” said Tim Kruschke of the BSH. He said the North Sea and Baltic were less affected than the Mediterranean or the North Atlantic, but temperatures in many areas still ranked among the highest of recent decades.

The warmer water can endanger marine animals by encouraging algal blooms and oxygen depletion. Some species may be forced into colder waters, while invasive species can spread more widely. Warmer seas also expand, contributing to higher sea levels, while their reduced ability to absorb carbon dioxide can further intensify climate change.

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These new highs in the southern North Sea and the 66 days with marine heatwaves off Helgoland show that extreme heat events are clearly affecting our home seas.