The rhythm of ocean warming has almost doubled since 2005 and more than a fifth of the global ocean surface suffered a severe heat wave in 2023, according to a report from the European Copernicus observatory published on Monday.
“Ocean warming can be considered our global warming watchdog. It has not stopped increasing since the 1960s. And since approximately 2005, the rate of warming of the oceans has doubled,” stressed oceanographer Karina Von Schuckmann, when presenting the 8th Copernicus report on the state of the oceans.
According to the report, The oceans have warmed by 1.05 watts per m2 since 2005, compared to 0.58 watts per m2 in previous decades.
This research reinforces the conclusions of the Intergovernmental Panel of Experts on Climate Change, IPCC.
In 2019, these UN-appointed experts considered it “likely” that the rate of ocean warming had “more than doubled since 1993.”
This warming is explained because, since 1970, the oceans have absorbed “more than 90% of the excess heat in the climate system”, caused by massive emissions of greenhouse gases by humans, according to the IPCC.
The oceans, which cover 70% of the Earth’s surface, They are one of the main regulators of climate on Earth. Warmer waters lead to more violent hurricanes and storms, with the destruction and flooding they bring.
This warming is also accompanied by an increase in heat waves at sea.
In 2023, 22% of the world’s oceans experienced at least one severe or extreme heat wave.
Impact on fishing
Marine heatwaves spread over wider areas and tend to last longer: the maximum average annual duration has doubled, from 20 to 40 days, since 2008.
In the northeastern Barents Sea, in the Arctic Ocean, “the (sea) bottom appears to have entered a state of permanent marine heat wave,” according to a study cited by Von Schuckmann.
Y In August 2022, a record temperature of 29.2°C was recorded in the coastal waters of the Balearic Islands“the highest regional surface water temperature in forty years,” the report also notes.
That same year, a marine heat wave in the Mediterranean Sea penetrated about 1,500 meters below the surface, illustrating how heat can spread throughout the water column.
Episodes of sea heat waves can cause migration and mass mortality of species, degrade ecosystems and reduce the ability of ocean layers to mix between the bottom and the surface, thus making the distribution of nutrients difficult.
They can also “have implications for fish productivity”, which has an impact on fishing, said Von Schuckmann.
The report also indicates that the acidity of the oceans, which absorb a quarter of the CO2 emitted by human activities, has increased by 30% since 1985.
Above a certain threshold, the acidity of seawater becomes corrosive to the skeletons and shells of corals, mussels, oysters, etc.
This threshold, considered a “planetary limit”, is likely to be exceeded “in the near future”, according to a report published last week by the Potsdam Institute for Climate Impact Research (PIK).