INTERVIEW. Ocean heat wave: yes, heat waves also hit the oceans

Did you know that heat waves also hit the oceans? This phenomenon is called “ocean heat waves”. But concretely, what is it, what are the consequences for the planet and? should we care? Robert Schlegel, research engineer at the Villefranche Oceanography Laboratory (LOV) and Bertrand Chapron from the laboratory Space and Air-Sea Interfaces of the French Research Institute for the Exploitation of the Sea (IFREMER) explains.

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What is a heat wave at sea?

If the oceans didn’t absorb heat, the air would be even warmer and therefore difficult to live in. But what we often forget is that the warmer the climate, the more water temperature rises so much so that it can sometimes exceed a certain threshold (determined according to the place and the season). This is called a marine heat wave or ocean heat wave. “This abnormally hot water can be described by its duration, intensity, rate of evolution and spatial extent” explains to POSITIVR Robert Schlegel, research engineer at the Villefranche Oceanography Laboratory (LOV).

But how does this phenomenon come about? “Sea heat waves are caused by a chain of favorable conditions, especially atmospheric (strong sunshine, high air temperature, weak wind), creating a heat dome similar to what can be observed over large agglomerations. This dome tends to reduce wind and thereby prevent adequate ventilation for cooling.”explains Bertrand Chapron of Ifremer.

While ocean currents favor this rise in heat, the main culprit today is: global warming† Indeed, according to a 2018 study, only 23% of ocean heat waves could be “natural.” The sea surface temperature and frequency of marine heat waves actually doubled between 1982 and 2016. In Europe, the Mediterranean and Baltic seas are most affected by these heat waves, as Bertrand Chapron mentions.

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Can we prevent them?

According to Bertrand Chapron, the data is formally: “They predict an increase in the frequency and area of ​​these anomalies” The coming years. But can we prevent these phenomena from happening? Robert Schlegel explains that it is imperative to act on our scale to avoid these oceanic heat waves.

How ? By rejecting less CO2 in the atmosphere“It’s like trying to avoid a cavity in the tooth. We can prevent cavities by brushing our teeth twice a day, but once the cavity is there, we have to go to the dentist to fix it.”

In other words, when the ocean heat wave is already there, there’s no getting around it, but it’s always possible to intervene in the ecosystem after it’s damaged to help it recover. Moreover, scientists take things very seriously, especially for the save coral reefs

What effects on marine ecosystems?

But it’s not just the corals that are suffering from these ocean heat waves. According to Robert Schlegel, all marine ecosystems are affected:

  • Displacement and/or change in the composition of species communities, or even the disappearance of certain species
  • Mass strandings of mammals
  • Massive mortality in certain species, such as gorgonians and corals
  • The modification of certain ecological niches
  • Some plankton, algae and parasites may have swarmed locally, as well as some pathogenic microorganisms and viruses for marine fauna and/or humans

“Ocean heat waves also cause localized moisture accumulation in the atmosphere through evaporation. This humidity can be carried back to the coasts where it gives rise to heavy rainfall (such as the rainfall in the Cevennes, in the south of France).”

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If we reduce our CO2 emissions, we can combat this alarming phenomenon in a sustainable way. So, ready to act for the good of the planet? To go further, discover 10 simple and concrete solutions from architects against the heat wave in the city.

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