«Level 4, never seen anything like it» - Corriere.it

Scientists call them Marine Heat Waves (Mhw): marine heat waves. They are of 5 levels, so far the most intense Mhw, level 4, was seen in 2011 in Western Australia: it lasted 132 days with a water warming of 4.9 degrees. Level 2 has never been exceeded in the Mediterranean. Now climatologists have identified another Mhw level 4 (extreme)but in an area where no one had imagined she would be interested: the Eastern North Atlantic.

Alarm

At about coasts of Great Britain and Ireland satellite instruments and oceanic buoys have found a warming of surface water by 4-5 degrees (in some areas even more) than the seasonal average for those areas. The warming of surface waters also extended to the North Sea (+1.25 degrees), the English Channel, the Baltic and the western Mediterranean. "Nothing like this has ever been seen", alarmed scientists comment, very worried about the fate of marine organisms from Iceland to the tropics, not used to this "heat" in one of the most fishy areas of the planet. Since 1982, Mhw has doubled, a scientific study found.

Water stratification

What oceanographers fear is the intensification of stratification of open waters two months ahead of schedule. That is, a temperature differentiation along the water column due to less mixing by cooler water at depth. These areas will warm further unless a strong Atlantic storm strikes. According to a 2022 study, the oceans have accumulated a huge amount of heat in the top 2,000 meters of the water column, largely absorbing global warming due to human activities since the industrial revolution. Another study showed that current warming of the Atlantic is unprecedented in the past 2,900 years. The warming of ocean waters also leads to an increase in salinity and wave power (+0.4% per year since 1948).