Environment: North Sea and Baltic Sea record temperatures in spring 2025
SURF
· 11.06.2025
In spring 2025, the Federal Maritime and Hydrographic Agency (BSH) recorded exceptionally high water temperatures in the North Sea and Baltic Sea. The entire North Sea experienced the warmest spring since analyses began in 1997, according to a BSH statement. The average temperature rose to 8.7 degrees, 0.9 degrees above the long-term average from 1997 to 2021. Almost the entire North Sea was at least 0.5 degrees warmer than usual at the surface, with significant upward outliers. This development is seen as a further sign of advancing climate change and could have far-reaching consequences for the marine ecosystem.
According to the BSH, the greatest temperature deviations occurred in the eastern North Sea off the Norwegian and Danish coasts. Temperatures there were up to 2 degrees above the long-term average - the highest spring temperatures recorded by the BSH for large parts of the northern and central North Sea since 1997. Significantly higher surface temperatures were also measured in the German part of the North Sea. Depending on the location, it was the fourth to sixth warmest spring since 1997, with values between 0.8 and 1.5 degrees above the long-term average.
Baltic Sea also affected
According to the BSH statement, the Baltic Sea was not spared from the warming either. It reached an average temperature of 5 degrees in spring, which corresponds to the sixth warmest spring since 1997 and is 1 degree above the long-term average. The south-western part of the Baltic Sea, which includes German waters and the Danish islands, was particularly affected. Temperatures here were more than 2 degrees above the long-term average, making it the warmest spring since current data began in 1997.
A marine heatwave was recorded at the Kiel lighthouse from 28 March to 21 May 2025 - the longest ever measured by the BSH at this station. Dr Claudia Hinrichs, climate scientist at the BSH, explains: "The marine heatwave lasted 55 days. During this time, temperatures averaged 2.6 degrees above the mean value from 1991 to 2020, with a maximum value of 4.3 degrees above average." These extreme events can have a significant impact on marine ecosystems and clearly demonstrate the increasing warming of the oceans.
Climate change as a cause
Dr Kerstin Jochumsen, Head of the Oceanography Department at the BSH, emphasises the importance of these measurements: "Our data show that the North Sea and Baltic Sea are continuously warming. This is a direct consequence of climate change and is increasingly changing the marine environment." The BSH's long-term series of measurements, particularly from the MARNET marine environmental monitoring network, are crucial for categorising and understanding these changes.
The BSH's analyses are part of the "Climate and Water" service, which is operated as part of the German Strategy for Adaptation to Climate Change (DAS). This data is used to advise various stakeholders in politics and society and to provide a basis for decision-making on adaptation strategies. The continuous warming of the North Sea and Baltic Sea emphasises the urgency of measures to combat climate change and the need to better protect marine ecosystems.
