The world's oceans are now heating at the same rate as if five Hiroshima atomic bombs were dropped into the water every second, scientists have said.
A new study released on Monday showed that 2019 was yet another year of record-setting ocean warming, with water temperatures reaching the highest temperature ever recorded.
An international team of 14 scientists examined data going back to the 1950s, looking at temperatures from the ocean surface to 2,000 meters deep. The study, which was published in the journal Advances in Atmospheric Sciences, also showed that the oceans are warming at an increasing speed.
While the past decade has been the warmest on record for global ocean temperatures, the hottest five years ever recorded all came in the last five.
"The upward trend is relentless, and so we can say with confidence that most of the warming is man-made climate change," said Kevin Trenberth, distinguished senior scientist in the Climate Analysis Section at the National Center for Atmospheric Research.
The study shows that while the oceans warmed steadily between 1955 and 1986, warming has accelerated rapidly in the last few decades. Between 1987-2019, ocean warming was 450% greater than during the earlier time period.
Lijing Cheng, the paper's lead author and an associate professor at the International Center for Climate and Environmental Sciences at the Chinese Academy of Sciences, said the ocean temperature was 0.075 degrees Celsius above the 1981-2010 average in 2019.
"There are no reasonable alternatives aside from the human emissions of heat trapping gases to explain this heating," Cheng said, adding that to reach this temperature, the ocean would have taken in 228,000,000,000,000,000,000,000 -- or 228 sextillion -- joules of heat.
"The Hiroshima atom-bomb exploded with an energy of about 63,000,000,000,000 Joules," Cheng said. "I did a calculation ... the amount of heat we have put in the world's oceans in the past 25 years equals to 3.6 billion Hiroshima atom-bomb explosions," he added.
That's equivalent to dropping roughly four Hiroshima bombs into the oceans every second over the past quarter of a century. But because the warming is speeding up, the rate at which we are dropping these imaginary bombs is getting faster than ever.
"We are now at five to six Hiroshima bombs of heat each second," said John Abraham, one of the authors of the study and a professor of mechanical engineering at the University of St. Thomas in Minnesota.
Oceans serve as a good indicator of the real impact of climate change. Covering almost three quarters of Earth's surface, they absorb the vast majority of the world's heat. Since 1970, more than 90% of the planet's excess heat went into the oceans, while less than 4% was absorbed by the atmosphere and the land, the study said.
But just because people live on land doesn't mean they are immune from the effects of the warming waters. Ocean warming has a profound impact on the entire world.
"If you want to understand global warming, you have to measure ocean warming," Abraham said.
For instance, both Hurricane Harvey, which killed at least 68 people in 2017, and Hurricane Florence, whose torrential rains flooded large parts of the US East Coast, were influenced by abnormally high temperatures.
While scientists say man-made climate change isn't solely to blame for tropical storms, studies have shown that higher temperatures can make them wetter and more damaging.
Rising temperatures also mean ocean waters have less oxygen and are becoming more acidic, which has a major impact on nutrients that feed marine wildlife. For example, when an ocean heat wave struck the waters of Western Australia in 2011, scientists noticed there were fewer dolphin births and the animal's survival rate dropped.
The warming is also changing currents and altering weather systems at a speed wildlife cannot keep up with.
"It is critical to understand how fast things are changing," Abraham added.
The scientists said that while the damage done to the oceans is in many ways irreversible, there is hope for the future.
"We will see continuous increase in ocean heat content in this century even if we can keep the global mean surface temperature (rise) well below 2 degrees Celsius (the goal of the Paris Agreement)," Cheng said.
However, he added that the speed of warming is entirely dependent on the world's actions on climate change.
"If we can reduce emissions, we can reduce the warming level, and then reduce the associated risks and loses," he said.
Trenberth added that an increasing price on carbon would help limit the warming.
"If the leaders of the world changed course, a revolution could take place over about 15 years ... this requires the leaders of China, and the US in particular, along with Europe, to take a strong leadership role and set the stage for the rest of the world to follow," he said.