Extreme ocean heat does not mean climate change is accelerating: study

BREST, France: An extraordinary jump in ocean temperatures in 2023 and 2024 was at the extreme end of expectations from global warming and would have been “practically impossible” without climate change, new research said on Wednesday.

The planet has been steadily warming for decades as emissions rise but the stunning leap in ocean temperatures was so far above the long-term trend that scientists debated if climate forecasts were still accurate.

Warmer seas cause marine heatwaves that influence monsoons, intensify tropical cyclones, and cause coral bleaching and mass extinctions of ocean life.

Between March 2023 and April 2024, global sea surface temperatures were 0.25 degrees Celsius above the previous record -- a substantially large margin in climate terms.

Such an event was “very rare”, said Jens Terhaar from the University of Bern in Switzerland, the lead author of a research paper on the anomaly published in the peer-reviewed academic journal Nature.

“We estimate that it occurs around every 500 years with the current warming trend,” he told AFP.

While not entirely unexpected, without the influence of human-driven climate change “such an event would have been practically impossible”, the authors concluded.

“If the warming trend increases, such events will happen more often and it if decreases, it will happen less often,” said Terhaar.

Scientists are unanimous that burning fossil fuels has largely driven climate change and pushed global temperatures to levels likely not seen in thousands of years.

Annual global average temperatures were the hottest on record in 2023 and 2024, and a prolonged and unprecedented heatwave in the oceans caused particular alarm and a search for answers.

Scientists questioned if the rate of global warming could be accelerating, and whether this event defied the projections of the best-available computer models used by scientists to anticipate climate behaviour.

Some research looked at whether other factors -- including reductions in cloud cover and a drop in heat-bouncing particles in the atmosphere -- could be helping drive up temperatures.

But the record-shattering spike in ocean temperatures was “not necessarily a sign of an unexpected additional acceleration of global warming”, Terhaar said.

“Scientists never believed that warming will be linear but that it will accelerate as long as emissions increase,” he added.