The world’s oceans were warmer in the 2010s than at any time in recorded history, with 2019 topping the list as the hottest year of all.

An international team of researchers from 11 institutes across the world calculated how much—and how fast—the planet’s oceans are warming and call for more to be done to combat climate change.

Using data from the Institute of Atmospheric Physics (IAP) in China and National Oceanic and Atmospheric Administration (NOAA) in the U.S., the study’s authors found 2019 ocean temperatures were around 0.075 degrees Celsius (0.135 degrees Fahrenheit) higher than the yearly average between 1981 and 2010.

According to the paper published in Advances in Atmospheric Science, the amount of heat energy required to make such a temperature change is 228 sextillion (228,000,000,000,000,000,000,000) Joules.

This means the oceans have absorbed the energy equivalent to 3.6 billion Hiroshima atomic bombs (63,000,000,000,000 Joules) in 25 years, lead author Lijing Cheng, an associate professor in oceanography at the IAP, said in a statement.

Cheng told Newsweek the warming is “highly likely irreversible” and could take hundreds, if not thousands of years to reverse. “This irreversibility means in addition to reducing greenhouse gases emission, we have to adapt to the changes and get prepare for the risks,” Cheng said.

The study also suggests the rate at which oceans are warming is speeding up as well. The researchers found the amount of warming between 1987 and 2019 was 450 percent of that between 1955 and 1986, while the last five years have been the warmest five years on records (for land as well as sea).

If we do not get a grip on greenhouse gases, we could see this acceleration of ocean warming continue—but if we limit temperature increases to 2C above pre-industrial temperatures, the rate of ocean warming could peak by 2040, said Cheng.

On a practical level, warming oceans means more ice sheet melting, coral reef bleaching and sea levels rising. It also means a less-oxygenated oceans because warmer water has less ability to dissolve oxygen. There is also an expected increase in the number of extreme events, such as marine heatwaves, said Cheng. Marine warming has also been linked to an increased number of extreme events on land.

“The price we pay is the reduction of ocean-dissolved oxygen, the harmed marine lives, strengthening storms and reduced fisheries and ocean-related economies,” said Cheng.

While a lot of attention has been given to global warming on land, less than 4 percent of heat has gone into the atmosphere, the researchers say. The vast majority and well over 90 percent of it has been absorbed by the world’s oceans.

“We know the ocean has huge heat capability and huge mass,” Cheng told Newsweek. “So the ocean can store a lot of heat due to global warming.”

The key to understanding the speed of global warming is the oceans, said co-author John Abraham, a professor of mechanical engineering at the University of St. Thomas in Minnesota.

“That’s where the vast majority of heat ends up. If you want to understand global warming, you have to measure ocean warming,” Abraham added.