In the spring and early summer of this year, a marine heatwave with sea temperatures up to four degrees above normal values was recorded off the coast of the British Isles. The triggers appear to be similar to those of the exceptional heatwave in the summer of 2023 in the North Atlantic Ocean: climate change and weak winds.

The North Atlantic Marine Heatwave of 2025 

The marine heatwave of 2025 (images 1 and 2) started earlier in the spring than the heatwave of 2023, but has many similarities with its predecessor. In both cases, large parts of the North Atlantic Ocean warmed to exceptionally high temperatures in just a few months. The marine heatwave of this year has recently decreased in intensity, but is not over yet. 

Four Recent Studies on the Marine Heatwave of 2023 

Four recent scientific studies published during the same period have further unraveled the causes and effects of the exceptionally warm North Atlantic Ocean of 2023. The studies show that the exchange of heat between the atmosphere and ocean was the main cause of the marine heatwave. Changes in ocean currents were not the cause and even had a cooling effect. 

1. Solar Radiation and Evaporation 

Research published in Geophysical Research Letters emphasizes the role of increased solar radiation and lower evaporation. Weaker winds led to less cooling of the seawater due to evaporation. The larger amount of solar radiation was related to less cloud cover. Although the solar radiation was above average in some locations, it was not enough to be the main cause of the entire North Atlantic heatwave.