Oceans may have entered "new normal" of extreme heat, scientists warn

In 2023, the Earth’s oceans experienced record-breaking marine heatwaves in terms of intensity, extent, and duration — with 96 per cent of the ocean surface affected and some heatwaves lasting over a year.

New research involving scientists from China, the USA, and Thailand suggests Earth’s oceans may have undergone a fundamental and potentially irreversible shift. Reduced cloud cover, weaker winds, and changing ocean currents were found to be key drivers behind the warming, beyond the expected effects of global warming and El Niño, EuroNews reports.

“We know that marine heatwaves have become increasingly common and more intense over time because of global warming. We also know that the El Niño that kicked off in 2023 allowed more heat to enter the ocean,” said Alex Sen Gupta from the University of New South Wales. “But these factors alone can't explain the incredible scale of the jump that began in 2023.”

The study raises concerns that oceans have transitioned to a hotter state, now becoming the "new normal."

Zhenzhong Zeng from the Southern University of Science and Technology in China stated, “figures suggest heat in the world’s oceans is accumulating exponentially,” a trend not predicted by current climate models.

This warming has far-reaching consequences: disruption of marine ecosystems, mass species migration, coral reef collapse, and intensified extreme weather events. Storm Daniel in 2023, which killed nearly 6,000 people, was found to be 50 times more likely due to high sea surface temperatures in the Mediterranean.

In 2024 and 2025, marine heatwaves continued, with Mediterranean waters reaching 26.01°C in June — 3-4°C above average. In May, the UK recorded a marine heatwave with parts of the North Sea and English Channel 4°C above normal.

Some experts caution against premature conclusions. “We don’t know what’s going to happen next year, and it [ocean temperatures] might just come back to something that’s much more, let’s say, normal,” said Neil Holbrook of the University of Tasmania.

Still, many agree on the urgency of deepening research. “While we urgently need to reduce our GHG emissions, it is critical that we also continue to measure, monitor and model what our future Earth is going to be like,” said Jaci Brown from Australia’s CSIRO. “If we don’t, we can’t prepare, and we are walking into the unknown with dire consequences for our future food, health and security.”

By Sabina Mammadli