The oceans are hit hard by climate change. They recorded a heat record in 2021, for the third year in a row. This is despite the presence of the La Niña phenomenon – a thermal anomaly of the surface waters of the equatorial Pacific, which lowers the global temperature of the planet. The last six years are, moreover, the warmest on record for the world’s seas, warn 23 American, Chinese and Italian scientists in a study published Tuesday, January 11. in the review Advances in Atmospheric Sciences.
According to their calculations, last year the oceans, to a depth of 2,000 meters, absorbed 14 zettajoules more than in 2020, or 14 trillion trillion joules, equivalent to 145 times production. world electricity in 2020. In the long term, warming affects the Atlantic and Southern Oceans more strongly, but the North Pacific has experienced an increase “Spectacular” heat since 1990 and the Mediterranean recorded a temperature record last year.
“The thermal content of the oceans [la chaleur accumulée par les eaux] is growing globally, and it is a primary indicator of human-induced climate change. ”, indicates one of the authors of the article, Kevin Trenberth, researcher at the National Center for Atmospheric Research in Colorado (United States).
“Without the oceans, we would suffer more”
Climate change is linked to a surplus of greenhouse gases, the concentration of which in the atmosphere is increasing due to human activities, in particular the combustion of fossil fuels (coal, oil and gas). This leads to a surplus of energy which heats the atmosphere and especially the oceans: they absorb 93% of this excess energy and store it over very long time scales.
If the average temperature on the earth’s surface has not broken a record in 2021 – the year is expected to rank as the 5e warmer – due to the influence of La Niña, the oceans continued to reach extremes. “They are much less affected by phenomena like La Niña”, explains American climatologist Michael E. Mann, director of the Earth System Science Center at Pennsylvania State University.
“Until we reach net zero emissions, their warming will continue and we will continue to break records for ocean thermal content, like this year.”, he warns. “It is only when we have managed to stabilize the CO concentration2 in the atmosphere that the amount of energy that will enter the oceans will decrease year after year, until it becomes zero ”, adds Benoît Meyssignac, researcher (Center national d’études spatiales) at the laboratory for spatial geophysics and oceanography in Toulouse, who did not participate in the study. “Fortunately, the planet has so many oceans: they limit global warming. Without them, we would suffer even more ”, adds the scientist.
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Global warming: the oceans recorded a new heat record in 2021