North Sea temperatures reach record high in 2025, second warmest year for Baltic Sea
Clean Energy Wire
Water temperatures in the North Sea reached record heights in 2025, according to Germany's Federal Maritime and Hydrographic Agency (BSH). With an annual average surface temperature of 11.6°C, the North Sea was warmer than it has ever been since BSH measurements started in 1969. In the Baltic Sea, 2025 was the second-warmest year since records began, following on the record year 2020.
Compared to the long-term average from 1997 to 2021, the average surface temperature in the North Sea was 0.9°C warmer last year. "Every month was well above the long-term average, with June and December setting records," said Tim Kruschke, head of marine climate studies at the BSH.
Warming is spreading to the depths and not just surface temperatures, BSH said. Heat stored in the North Sea increased to 1.46 million petajoules (PJ), about 35,000 PJ more than the year before. This difference is around three times as high as Germany’s primary energy consumption in 2025.
In the Baltic Sea, the annual average surface temperature reached 9.7°C, which is 1.1°C above the long-term average. In almost every region, surface temperatures were more than 0.5°C higher than the long-term average.
Additionally, marine heat waves are becoming a more common phenomenon in Germany’s neighbouring waters. These extraordinarily warm periods last at least five days and increase pressure on marine ecosystems, BSH wrote.
The agency warned that these increasing temperatures are contributing to rising sea levels, as higher temperatures lead to water expansion and melting glaciers and ice sheets.
In turn, higher sea levels increase the risks of more severe storm surges and flooding. According to the Intergovernmental Panel on Climate Change (IPCC), global sea levels could rise by 0.63 to 1.01 metres until 2100, if no far-reaching action is taken to reduce greenhouse gas emissions.
