The rate of ocean warming has almost doubled since 2005 and more than a fifth of the world’s ocean surface will experience a severe heat wave in 2023, according to a report from the European Copernicus Observatory published Monday.
“Ocean warming can be considered our sentinel of global warming. It has continued to increase since the 1960s. And since around 2005, the rate of ocean warming has doubled,” emphasized oceanographer Karina Von Schuckmann during a videoconference, presenting the 8e Copernicus State of the Oceans Report.
The oceans are warming by 1.05 watts per m2 since 2005, compared to 0.58 watts per m2 in previous decades, according to the report.
This work consolidates the IPCC reports. In 2019, these climate experts mandated by the UN considered it “probable” that the rate of warming of the oceans had “more than doubled since 1993”.
This warming is explained by the fact that the oceans have absorbed “more than 90% of the excess heat of the climate system” since 1970, caused by massive emissions of greenhouse gases by humanity, according to the IPCC. .
The oceans, which cover 70% of the earth’s surface, are a major regulator of the earth’s climate. Warmer waters bring more violent hurricanes and storms, with their attendant destruction and flooding.
This warming is also accompanied by an increase in marine heatwaves. Thus, 22% of the world’s oceans experienced at least one severe or extreme heat wave in 2023.
An impact on fishing
More widespread, marine heat waves also tend to become longer, with an average annual maximum duration which has doubled since 2008, from 20 to 40 days.
In the northeast of the Barents Sea, “the bottom [de la mer] appears to have entered a state of permanent marine heat wave,” according to a study cited by Mme Von Schuckmann.
And 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”, also points out the report.
The 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.
Marine heatwave episodes can lead to migrations and episodes of mass mortality of species, degrade ecosystems, but also reduce the capacity of ocean layers to mix between the bottom and the surface, thus hindering the distribution of nutrients.
They can also “have implications on fish productivity”, impacting fishing, underlined Mme Von Schuckmann.
The report also notes 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 for the skeletons and shells of corals, mussels, oysters, etc.
This threshold, considered a “planetary limit”, should be crossed “in the near future”, according to a report published last week by the Potsdam Institute for climate impact research (PIK).