The accelerated warming of the oceans, which has nearly doubled since 2005, is leading to increasingly frequent marine heatwaves, destabilizing marine ecosystems, according to a scientific report.
The pace of ocean warming has nearly doubled since 2005, with more than one-fifth of the world’s ocean surface experiencing severe heatwaves in 2023, according to a report from the European Copernicus Observatory published on Monday. “Ocean warming can be seen as our sentinel of climate change. It has been consistently rising since the 1960s. Since around 2005, the rate of ocean warming has doubled,” explained oceanographer Karina Von Schuckmann during a virtual presentation of Copernicus’ eighth annual report on the state of the oceans.
Absorbed Heat
The report highlights that ocean warming is accelerating, with a rate of 1.05 watts per square meter since 2005, compared to 0.58 watts per square meter in previous decades. This indicates that the amount of heat absorbed by each square meter of ocean has nearly doubled during this period. The findings of this report reinforce the forecasts of the Intergovernmental Panel on Climate Change (IPCC), which estimated in its 2019 report that it was “likely” the rate of ocean warming had “more than doubled since 1993.”
According to scientists, the oceans have absorbed over 90% of the excess heat caused by greenhouse gas emissions since 1970. Covering 70% of the Earth’s surface, they play a crucial role in climate regulation. However, rising ocean temperatures contribute to the formation of more violent hurricanes and storms, leading to destruction and flooding. Meanwhile, the phenomenon of marine heatwaves is intensifying: 22% of the oceans experienced at least one severe or extreme heatwave in 2023. These heatwaves are also becoming longer, with their average annual duration doubling since 2008 to reach 40 days.
Planetary Limits
Certain regions, such as the northeastern Barents Sea (off the coasts of Norway and Russia), now appear to be facing permanent marine heat, according to a study cited by Von Schuckmann. In August 2022, coastal waters near the Balearic Islands (Spain) recorded a record temperature of 29.2°C, the highest in 40 years, according to the same report. That year, a marine heatwave in the Mediterranean penetrated approximately 1,500 meters below the surface, illustrating how heat can spread throughout the entire water column.
The consequences of these heatwaves are severe: species migrations, mass mortality, ecosystem degradation and disruption of fish productivity, directly impacting fisheries. The report also notes that ocean acidity, which absorbs a quarter of the CO2 emitted by human activities, has increased by 30% since 1985. Beyond a certain threshold, seawater acidity becomes corrosive to the skeletons and shells of corals, mussels, oysters and other marine organisms. Labeled a “planetary limit,” this critical threshold could soon be crossed, according to a report released last week by the Potsdam Institute for Climate Impact Research (PIK).
With AFP
