BSH report: Extreme winter in the North Sea and Baltic Sea - but still too warm
SURF Redaktion
· 16.03.2026
According to the BSH report, the water temperature in the North Sea reached a new high of 9.6 degrees Celsius in December 2025 - the warmest December since the data series began in 1996/97. Just a few weeks later, however, temperatures fell to 5.9 degrees in February, 0.5 degrees below the long-term average. The picture was similar in the Baltic Sea: in December, it recorded the third warmest value since 1996/97 at 6.1 degrees, before temperatures plummeted to 0.7 degrees in February.
The Federal Maritime and Hydrographic Agency analyses these extreme fluctuations and places them in the context of long-term global warming. In the winter of 2025/26 as a whole, the North Sea averaged 7.7 degrees Celsius, around 0.3 degrees above the long-term average from 1996/97 to 2020/21. The Baltic Sea was 3.3 degrees, around 0.4 degrees above the comparable value. Both seas thus recorded their tenth and eleventh warmest winters since measurements began.
Warmer in the north, colder on the German coasts
According to the report, the regional differences were particularly marked. In December, temperatures in the North Sea were above the long-term average across the board. In the transition area to the Baltic Sea, the deviations reached up to two degrees. January brought a trend reversal: The northern North Sea remained warmer than usual, while the southern areas showed cooler values. The average of 7.5 degrees was only 0.3 degrees above average.
The Baltic Sea also presented a varied picture over the entire winter. Central and northern areas remained warmer than average, while the south-west, including German waters, was colder than usual. February intensified this trend dramatically: temperatures fell well below average across the board. Off the German coast and around Denmark, the values were up to two degrees below the long-term average.
East wind brings arctic cold
"The winter of 2025/2026 illustrates how strongly the weather influences sea surface temperatures in the short term, even in times of long-term global warming caused by humans," explains Dr Tim Kruschke, Head of the Marine Climate Division at the BSH. Southeasterly winds from mid-January to mid-February transported cold air from Eastern Europe over German coastal waters. This meteorological constellation led to a rapid drop in temperatures, and within a few weeks the values were well below the record levels of December. The weather extremes show the range of natural fluctuations that are superimposed on the long-term warming trend. In addition to the low temperatures, this was also reflected in the heaviest ice formation in a decade and a half.
The winter of 2025/2026 illustrates how strongly the weather influences the sea surface temperature in the short term, even in times of long-term global warming caused by humans." (Tim Kruschke, BSH)
Massive ice formation on the Baltic Sea coast
According to the BSH, the eastern part of the German Baltic Sea coast experienced the longest ice winter in 15 years. At the beginning of January, large areas of ice formed in the Greifswalder Bodden and Szczecin Lagoon, which persisted into March. Persistent easterly winds and frost created wide bands of ice off the east coasts of Usedom and Rügen. "The thick ice off Usedom and Rügen severely hindered shipping traffic. When it broke away, it drifted out to sea. All shipping traffic in and out of the Baltic Sea had to watch out for the ice. Such severe ice winters are now rare," explains Dr Jürgen Holfort, head of the BSH ice service. Further west, ice occurred mainly in sheltered coastal areas. In February, ice formed briefly in the fjords up to Flensburg. On the North Sea coast, isolated patches of ice formed in the northern Wadden Sea and on the Elbe. With milder weather at the end of February, the ice melted quickly, except in the eastern Baltic Sea. The ice season for the entire Baltic Sea continues until May.
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