Record marine heatwaves across globe could signal climate tipping point, new study says

Record marine heatwaves occurred in 2023, damaging ecosystems and jeopardising the fishing industry across the whole world, according to a new study published in the journal Science.

The heatwaves, intense and prolonged episodes of unusually warm ocean temperatures, lasted four times as long as the historical average and some of the events, described as “unprecedented in their intensity, persistence, and scale” went on for longer than 500 days. As a result there are “serious economic consequences,” the researchers said, due to “mass coral bleaching” and the threat to fisheries and biodiversity.

The Portuguese Algarve recently experienced a marine heatwave and the phenomenon, the scientists now warn, has been taking place around the globe covering 96% of the planet’s oceans including the North Atlantic, Tropical Pacific, South Pacific, and North Pacific. In the North Atlantic, a marine heatwave or MHW began in mid-2022 and did not stop for nearly a year and a half. In the Southwest Pacific too, there was a heatwave that stood out for its “vast spatial extent and prolonged duration.”

Here is a visualization of the remarkable marine heatwave in the Mediterranean.

These temperatures are incredibly anomalous and are among the highest ever observed for this time of year. pic.twitter.com/1EkrfbABhi

— Andrew Austin-Adler (@WeathermanAAA_) July 7, 2025

Thinning clouds, weaker winds, and shifting ocean currents

The team of scientists from China, Thailand, and the United States applied analysis tools to combined satellite observations and ocean reanalysis data, with some of it taken from the ECCO2 (Estimating the Circulation and Climate of the Ocean-Phase II) high-resolution project.

“Human-driven climate change”, the team says, is “widely understood” to be a factor, their findings pointing to a range of regional drivers behind the marine heatwaves, from alterations in ocean currents, to rising solar radiation attributed to thinning cloud cover, and a drop in ocean evaporation and cooling due to reduced winds. In the Tropical Eastern Pacific, the start of the El Niño climate cycle, which sees normal east-to-west trade winds diminish or reverse, sending warm water towards the east, coincided with a peak water temperature anomaly of 1.63°C.

Tipping point?

Overall the mass marine heatwaves could be a warning sign of “deeper, system-wide climate changes” and signal a tipping point, the team behind the report have said. Tipping points are a short-hand for a point of no return, or the onset of irreversible change to a system’s cycles and feedback loops.

Study author Zhenzhong Zeng, from the Southern University of Science and Technology in China, said the data indicates a “fundamental shift in ocean-atmosphere dynamics” and an exponential rise in the temperature of the world’s oceans.

A severe marine heat wave is unfolding in the Mediterranean Sea.

Sea surface temperatures have been record-breaking on more than 50 days this year, with the current average of 26˚C (79˚F) equal to the typical annual maximum — almost two months earlier than normal 🧵 pic.twitter.com/Dh34FPLvCR

— Ben Noll (@BenNollWeather) July 4, 2025

Marine heatwaves are not only bad news out at sea. Warmer oceans are associated with extreme weather events, such as rainfall and flooding, that not only affect those on land but become harder to predict. Warm seas also warm up territories more quickly, as cooling sea breezes are replaced by warm air coming inland feeding into droughts and wildfires.