An unprecedented heat wave is currently sweeping the waters of the Atlantic. In June, the ocean from southern Iceland to Africa experiences particularly intense heat waveswith temperature anomalies greater than 5°C off the British Isles. This extreme phenomenon, which is causing great concern, will lead to an unseen slaughter of marine life, according to scientists.
A similar heat wave hit the waters of the Mediterranean Sea last year, notably with a difference of more than 6 degrees compared to the normal before Marseille in mid-July 2022 and consequences for around fifty marine species. Episodes that could well repeat themselves in the coming years due to global warming, with even greater force.
What do the scientists say?
The warming of the Atlantic is no exception. Between the months of March and May In fact, the average temperature at the surface of the oceans has reached an all-time high in 174 years of measurementAccording to the US Oceanographic Administration (NOAA), the temperature is 0.83 °C higher than the 20th century average. This marine heatwave, with temperatures exceeding 23°C in the North Atlantic, does not therefore come as a complete surprise to scientists, who know that the oceans absorb 90% of the heat generated by the greenhouse effect.
But the localization of this phenomenon surprised the experts. “Such temperature anomalies are unknown in this part of the North Atlantic”underlines Daniela Schmidt, Professor of Earth Sciences at the University of Bristol, quoted by the British Science Media Center.
“What’s surprising is that it’s extremely fast”also supports Jean-Pierre Gattuso, research director at the CNRS (National Center for Scientific Research) and co-editor of a report by the IPCC (UN climate experts).
The European marine heatwave continues to break through the ceiling. It is rated ‘extreme’ (category 5) by NOAA throughout Scotland. Yesterday the temperature of the North Atlantic reached 23.05 °C (an anomaly of +1.22 °C).
In June there is no precedent. From far away. pic.twitter.com/IaSGsake9h— dr Serge Zaka (Dr Zarge) (@SergeZaka) June 19, 2023
What is its origin?
Several hypotheses have been put forward to explain this extreme phenomenon, such as the reduction in wind-blown Saharan dust or the reduction in sulfur emissions from ships, two types of aerosols that usually have a cooling effect on the atmosphere. But “it remains at the hypothetical stage,” estimates Jean-Baptiste Sallée, oceanographer and climatologist at the CNRS.
As for the El Niño phenomenon, which warms the waters for six to nine months and occurs about every five years, it seems too underdeveloped to have an impact on the North Atlantic. “We expect more of an effect next spring,” explains Juliette Mignot, oceanographer at the IRD (Institute of Research for Development).
The researcher envisions a possible “change in ocean currents,” or meteorological phenomenon, that would overlay global warming. The origin of this marine heat wave therefore remains unclear for the time being.
What are the risks to biodiversity?
Whatever the origin of this heat wave in the sea, Scientists predict there will be a “mass extinction” of marine species, including corals and invertebrates. But these dramatic consequences, which take place under the water surface, will remain invisible.
According to Jean-Pierre Gattuso, during the heat waves in the Mediterranean, about fifty species (corals, gorgonians, sea urchins, molluscs, bivalves, posidonia, etc.) were affected by “massive deaths between the surface and 45 meters deep”. Co-author of an article on this topic. Other species migrate more toward the poles. “The waters of Norway and Iceland, for example, are becoming richer in fish,” to the detriment of the countries in the inner-tropical zone, according to the researcher.
By the end of the century In its most pessimistic scenario, the IPCC predicts a 50-fold increase in the frequency of these ocean heat waveswith episodes whose intensity is multiplied tenfold.
The editors recommend
Subscribe to the RTL info newsletter with your RTL account to follow all the news every day
Continue reading