Global ocean temperatures soared to the highest level on record this week

Why are ocean waters getting hotter? Professor Gordon McBean explains the implications for the planet and its ecosystems as ocean temperatures continue to rise.

The temperature of the planet’s oceans rose to new heights this week, setting a new record with no sign of cooling down.

The average global ocean surface temperature hit 20.96 degrees Celsius (69.7 Fahrenheit) at the end of July, according to modern data from the European Union’s Copernicus Climate Change Service, beating the previous record of 20.95 degrees Celsius set in 2016. The Copernicus ocean data goes back to 1979.

Scientists say the world needs to brace for ocean temperatures to keep rising as the arrival of El Niño – the natural climate fluctuation that originates in the tropical Pacific Ocean, and has a warming impact – layers on top of human-caused global warming.

Kaitlin Naughten, an oceanographer at British Antarctic Survey, said the data from Copernicus painted an alarming picture for the health of the oceans.

“Other datasets may give slightly different values – for example, [the US National Oceanic and Atmospheric Administration] is reporting that last April was still very slightly warmer than now,” she told CNN.

But what’s clear, she said, is “that current sea surface temperatures are exceptionally and unseasonably warm” and bringing wide-ranging implications, “especially for complex ecosystems such as coral reefs.”

Gregory C. Johnson, an oceanographer at NOAA, said sea surface temperatures have soared this year. “What we’re seeing is a massive increase. It’s about 15 years worth of the long-term warming trend in a year,” he told CNN.

The heat could increase even further. Surface temperatures tend to remain high from August through to September before starting to decline, said Johnson. “There’s still room to have warmer sea surface temperatures” this year.

Some marine heat waves this year have particularly shocked scientists for just how unprecedented they are, and the damage they are causing. Ocean heat can lead to the mass bleaching of coral reefs, as well as the death of other marine life and increased sea level rise.

In the Florida Keys, a marine heat wave has pushed ocean temperatures to record-breaking, “hot tub” levels, leaving multiple coral reefs now completely bleached or dead.

A “totally unprecedented” heat wave in the North Atlantic off the coasts of the UK and Ireland in June – defined as “extreme” by NOAA – saw temperatures up to 5 degrees Celsius (9 Fahrenheit) hotter than usual, sparking concerns about the impacts on marine life.

Samantha Burgess, the deputy director of Copernicus, said the heat in the North Atlantic was astonishing.

“We’ve never seen that kind of extreme marine heat wave for that time of year … to see them in the open ocean, to see them in spring – that’s very surprising,” she told CNN in an interview last week.

Warmer ocean water also has a climate impact. Oceans play a vital role as a buffer against the climate crisis by absorbing planet-heating pollution. Warmer water does this less effectively, meaning more carbon is left in the atmosphere, fueling global warming.

Some scientists are concerned that the ocean temperature records set this year could mark the start of an alarming trend for ocean heat.

“We are continuing to put greenhouse gases in the atmosphere,” Johnson said. “And so, in the long term, sea surface temperatures are just going to continue to increase until we as a society decide to to cut our use of fossil fuels very substantially.”