Since measurements began in 1969, the average temperature in the North Sea reached a new high of 11.6 degrees Celsius. This means that the North Sea was warmer than ever before in 2025, according to the Federal Maritime and Hydrographic Agency (BSH) in Hamburg.

The surface temperature in 2025 was 0.9 degrees above the long-term average for the years 1997 to 2021. The warming trend is also continuing in the deeper water layers, particularly in the southern North Sea and in the German Bight.

The Baltic Sea is also continuing to warm. There, 2025 was the second warmest year since the BSH data series began in 1990. The average surface temperature was 9.7 degrees Celsius, 1.1 degrees above the average for the years 1997 to 2021.
According to the BSH, the data not only shows long-term developments, but also new extremes. For example, a marine heatwave lasting 55 days was recorded in the Baltic Sea in spring 2025 - an unprecedented event. At the same time, the ice winter of 2025/2026 made it clear that extreme cold phases can continue to occur, particularly in the Baltic Sea, despite a climate that is becoming warmer in the long term.

kdk, Tagesschau