Waters around the UK and Ireland have recently been hit by a category 4 (extreme) marine heat wave as the North Atlantic Ocean continues to experience extreme heat. An article published by InfoClima.ro explains what marine heat waves are, why they are dangerous and how they manifest in the Black Sea.

What are marine heat waves?

As the average global temperature rises, so does the temperature of the oceans and seas. This increases the likelihood of marine heat waves. Marine ecosystems can adapt to certain temperature criteria, but cannot adapt to extreme events such as marine heat waves.

We are already used to atmospheric heat – periods of high temperatures (compared to normal temperature values ​​in a certain region and at a certain time of the year) that last for several days (usually more than three days in a row).

Globally, the frequency, duration and intensity of heat waves have increased compared to pre-industrial times, according to the latest IPCC report. Climate projections show that this change in heat wave characteristics will continue as global average temperatures rise.

But there are also heat waves that occur in seas and oceans called marine heat waves. During a marine heat wave, the surface temperature of the ocean or sea is high—compared to the climatic conditions for a particular region and time of year—for a long period of time (at least 5 consecutive days).

Why do sea heat waves occur?

Marine heat waves are caused by several factors that vary by event and region.

Thus, marine heat waves are generated by ocean currents that lead to regions with higher ocean surface temperatures compared to neighboring regions.

Heat exchange between the atmosphere and the ocean (the atmosphere heats the surface of the ocean) also contributes to heat waves.

Wind also affects heat waves: they can increase or decrease the sea heat. Large-scale atmospheric processes over relatively long periods of time, such as El Niño (right clip), can change the probability of marine heat waves for certain regions.

Sea heat in the Black Sea

In the Black Sea, the average duration of sea heat was from 13 to 19 days. For the analyzed time interval (1895-2022), an increase in the frequency of marine heat waves from 0.75 to 2.25 cases per 10 years was observed, especially in the eastern region of the Black Sea.

Thus, these heat waves exist not only in the Black Sea, but their number and duration have increased since 1985.

Read the full article at infoclima.ro