Every year around this time, the North Sea is at its coldest. But nowadays, the seawater cools down less strongly than before. Over the past 40 years, the North Sea has warmed by about 1.7 degrees. This warming varies by season and region. A warmer North Sea also leads to more precipitation, especially in autumn in coastal areas when the wind blows from the sea.
North Sea is warming
Thanks to satellites, we know quite precisely how warm the surface seawater of the North Sea is and how that temperature has changed. Between 1982 and 2024, the average temperature was about 10 degrees (image 1, left). The water is somewhat warmer along the Dutch coast and colder towards the Atlantic Ocean, beyond Scotland.
The warming differs by area (image 1, right). Close to the coast, the temperature has risen the most, less so towards the Atlantic Ocean. For the Dutch coast, it is about 0.4 degrees per 10 years. North of Scotland, it is less than 0.2 degrees per 10 years. This has increased the temperature differences within the North Sea.
Temperature changes strongly throughout the year
The North Sea is not very deep. In the south, it is 20 to 50 meters deep, towards Norway it increases to 200 to 300 meters. In spring and summer, mainly the upper 20 to 30 meters warm strongly due to the sun. In autumn and winter, this water cools down again (see animation in image 2).
At the coast, the differences throughout the year are the greatest: from less than 2 degrees in February to more than 20 degrees in August. That is a difference of about 18 degrees. North of Scotland, where the sea is much deeper, the temperature fluctuates much less: between about 7 and 14 degrees.
Also notable is the difference between winter and summer. In winter, it gets warmer as you go from the cold coast out to sea. In summer, it is the opposite: the water near the coast is warmer than further out at sea.
Warming stronger in summer than winter
The magnitude and pattern of warming is not the same in all seasons (image 3). The strongest warming is seen in spring (0.5 degrees per 10 years at the coast in the square in image 3), the least warming in autumn (0.3 degrees per 10 years in the same area). In summer, warming is strongest in the middle of the North Sea, in other seasons near the coast.
Warming over land stronger than over sea
The temperature of the North Sea at the Dutch coast is on average 1.2 degrees higher than in De Bilt (image 4). The year-to-year variations are almost the same and this also applies to the average warming over the entire period (+1.7 degrees). Further offshore, the warming proceeds more slowly. The main cause is that evaporation over the sea increases more strongly with warming than over land. And evaporation has a cooling effect.
Why is the sea warmer than the land?
It takes more energy to warm the sea than the land, which is why the sea warms more slowly in spring and summer than land, but also cools much more slowly in autumn and winter (image 5). And it is precisely those mild winters that cause the annual average above the sea to be higher. In summer, it becomes almost as warm over land as over sea.
Why is the warming of the North Sea important?
The North Sea acts as a heat battery: the heat stored in summer is released again in winter. This causes mild winters in the Netherlands. Especially in autumn, a warm North Sea feeds the development of showers when the wind is from the west, which give a lot of precipitation mainly on the coast. The warmer the North Sea, the more intense those showers.