Scientists sound alarm about ocean warming hitting critical level

By Stephen Beech

The rate of ocean warming has more than quadrupled over the past four decades, warns a new study.

Sea surfaces are heating up four times faster now than in the 1980s, say scientists.

Research shows that ocean temperatures were rising at about 0.06 degrees Celsius per decade in the late 1980s, but are now increasing at 0.27 degrees Celsius per decade.

Scientists say their findings, published in the journal Environmental Research Letters, help to explain why 2023 and early 2024 saw unprecedented ocean temperatures.

Study lead author Professor Chris Merchant, of the University of Reading, said: “If the oceans were a bathtub of water, then in the 1980s, the hot tap was running slowly, warming up the water by just a fraction of a degree each decade.

"But now the hot tap is running much faster, and the warming has picked up speed.

"The way to slow down that warming is to start closing off the hot tap, by cutting global carbon emissions and moving towards net-zero.”

He says that accelerating ocean warming is driven by the Earth's growing "energy imbalance" – whereby more energy from the Sun is being absorbed in the Earth system than is escaping back to space.

Merchant said the imbalance has roughly doubled since 2010, in part due to increasing greenhouse gas concentrations, and because the Earth is now reflecting less sunlight to space than before.

Global ocean temperatures hit record highs for 450 days straight in 2023 and early 2024.

Merchant said: "Some of this warmth came from El Niño, a natural warming event in the Pacific.

"When scientists compared it to a similar El Niño in 2015-16, they found that the rest of the record warmth is explained by the sea surface warming up faster in the past 10 years than in earlier decades."

He says 44% of the record warmth was attributable to the oceans absorbing heat at an accelerating rate.

Merchant added: "The findings show that the overall rate of global ocean warming observed over recent decades is not an accurate guide to what happens next.

"It is plausible that the ocean temperature increase seen over the past 40 years will be exceeded in just the next 20 years.

"Because the surface oceans set the pace for global warming, this matters for the climate as a whole.

"This accelerating warming underscores the urgency of reducing fossil fuel burning to prevent even more rapid temperature increases in the future and to begin to stabilize the climate."