Heatwaves will soon be constant in the oceans and it’s dramatic

Heatwaves will soon be constant in the oceans and it's dramatic

You may think that water at almost 25°C is great news for your holidays, but in reality it is a disaster for the planet.

CLIMATE – “We are locked in a situation where, by 2050, all of the ocean world will be close to a state of heat wave sea ​​level almost constant”, warns Robert Schlegel, a researcher at the Institut de la Mer de Villefranche (IMEV), interviewed by The HuffPost.

At the opening of the ocean summit in Lisbon on Monday June 27, Antonio Guterres, the UN secretary general, declared an “ocean emergency”. Emmanuel Macron goes there this Thursday, June 30.

And for good reason, the ocean undergoes not only the global warming but it is also hit by increasingly frequent sea heat waves. These episodes are little known and little publicized, but far from being rare, the Mediterranean Sea is currently under the yoke of extreme heat. You may think that water at almost 25°C is great news for your holidays, but in reality it is dramatic for the planet.

“With the exception of the Alboran Sea (between Morocco and Spain), the entire western Mediterranean has been experiencing a marine heat wave since around May 16”, details Robert Schlegel. Sea surface temperature (SST) peaks at +5°C above average along the coasts of Spain, France and Italy, as seen in the visualization below based on data from the Copernicus Marine Service.

Some parts of the Mediterranean are more than +5°C warmer than average.  (Photo: Copernicus)

Some parts of the Mediterranean are more than +5°C warmer than average. (Photo: Copernicus)

Some parts of the Mediterranean are more than +5°C warmer than average. (Photo: Copernicus)

These heat waves occur when ocean temperatures cross an extreme threshold for more than five consecutive days. Robert Schlegel explains that this threshold is calculated using historical records of temperatures “based on an average of 30 years (for example, 1981-2010) and are determined by smoothing the average daily temperatures over these years”. This is what is called in science a “climatology” and it represents the average temperature expected for each day of the year.

In a century, 50% more days of sea heat wave

In the current climate, ocean heat waves only last a fortnight in the Mediterranean. In the worst scenario predicted by the IPCC, with a warming of +5°C, the simulations predict that they will be four months longer and four times more intense, reports a study on the evolution of ocean heat waves in the Mediterranean from CNRS.

The scientists add that only the scenario of a warming limited to +1.5 degrees compared to 1990 would make it possible to stem the worsening of these heat waves.

With global warming, they will be longer, but also much more numerous. “Between 1925 and 2016, the number of annual days of marine heat waves in the world increased by more than 50%”, reports Carole Saout-Grit, physicist oceanographer, contacted by The HuffPost.

These figures come from a study in the scientific journal Nature Climate Changein which researchers establish a direct link between the increase in these heat waves and the long-term warming of the oceans.

Total number of marine heatwave days in the world from 1982-2016.  (Photo: Nature Climate Change https://www.nature.com/articles/s41467-018-03732-9)

Total number of marine heatwave days in the world from 1982-2016. (Photo: Nature Climate Change https://www.nature.com/articles/s41467-018-03732-9)

Total number of marine heatwave days in the world from 1982-2016. (Photo: Nature Climate Change https://www.nature.com/articles/s41467-018-03732-9)

Even if we manage to contain warming to +2°C, “almost all of the oceans will experience more frequent and longer marine heat waves”, continues the researcher.

As for the consequences, past sea heat waves predict major changes in ecosystems. In 1999, 2003 and 2006, the Mediterranean was hit by a heat wave causing “many cases of massive mortality of species”, deplores the National Center for Scientific Research (CNRS).

The equator, soon a dead zone?

A hecatomb which is nothing compared to that caused by “Le Blob”. We are not talking here about the single-celled species that looks like a sponge, but about a marine heat wave that lasted three years, on the west coast of North America between the end of 2013 and 2016. The excessively hot water during this period stopped the growth of phytoplankton, a species at the base of our food chain.

Less intense heat waves also cause considerable rebound effects on ecosystems. Under the effect of heat anomalies, the corals are covered with a white shroud. Indeed, the stressed organisms expel the micro-algae with which they live in symbiosis and turn white. Because of this bleaching which makes them vulnerable, “it is almost certain that the Great Barrier Reef will have completely disappeared within 10 to 20 years”, adds Robert Schlegel.

Another consequence is that these heat waves accelerate the migration of species towards the poles where the water temperature is lower. “It’s a problem at the equator, which could (but we’re not sure) become a dead zone, because there won’t be any organisms on the planet that can adapt to the high temperatures” , continues the researcher.

save or perish

What is certain, however, is that species unable to migrate will perish with the increase in temperature. In the Arctic, for example, ecosystems that rely on ice will be eradicated as the sea ice melts.

Admittedly, we are not on the road to 5°C warming, but the direction taken by humanity today is far from sufficient to prevent the ocean from overheating. If we continue on our current trajectory between now and 2050, Robert Schlegel poses a much more pessimistic assessment: “most of the world’s oceans will be forced to change. But changing into what is hard to say.”

Faced with this alarming observation, it is difficult to find a glimmer of hope. But if we succeed in controlling our emissions, it is possible that some ecosystems will survive. According to the scenarios of study on marine projections in the 21st century, with a temperature increase of +2.5°C, most oceans will experience “category 1 (moderate) and 2 (strong) events”, which is bad, but we can live with it. If we keep the commitments made during COP26, this trajectory to “save” the Blue Planet is still possible.

This article was originally published on The HuffPost and has been updated.

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