The Earth’s oceans hit record high temperatures last year as the rate of global warming continued to accelerate, researchers have said.

The rate of heat introduced to the planet’s oceans over the last 25 years is equivalent to the energy produced by 3.6 billion atomic bombs, according to scientists.

Climate change has fuelled rapid rises in global surface air temperature since the 1950s, with 2016 the hottest year on record.

A new study mapping the impact of warming on the oceans found waters in 2019 were at their hottest in recorded human history – increasing by 0.075C above the 1981-2010 average.

Oceans provide a good picture of the planet’s warming as they trap more than 90 per cent of the excess heat stored on Earth, scientists say. 

“This measured ocean warming is irrefutable and is further proof of global warming. There are no reasonable alternatives aside from the human emissions of heat trapping gases to explain this heating,” said Lijing Cheng, lead author of the study, published in the journal Advances In Atmospheric Sciences.

To have increased to the level it has, the ocean will have absorbed 228,000,000,000,000,000,000,000 (228 sextillion) joules of energy.

“That’s a lot of zeros indeed,” said Mr Cheng, associate professor with the International Centre for Climate and Environmental Sciences at the Chinese Academy of Sciences. “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.”

Researchers assessed data from all available sources including 3,800 Argo floats across the planet’s seas and oceans.

Assessing the data with new methods of analysis to compare with heat trends stretching back as far as the 1950s, they found the last five years have been the warmest on record.

“It is critical to understand how fast things are changing,” said John Abraham, co-author and professor of mechanical engineering at the University of St Thomas in the United States. “The key to answering this question is in the oceans – that’s where the vast majority of heat ends up. If you want to understand global warming, you have to measure ocean warming.”

He added: “Global warming is real, and it’s getting worse. And this is just the tip of the iceberg for what is to come. Fortunately, we can do something about it: We can use energy more wisely and we can diversify our energy sources. We have the power to reduce this problem.”

Alongside long-term trends, sudden bursts of warmth – such as a north Pacific heatwave from 2013 to 2015 dubbed “the blob” by researchers – can have catastrophic effects on ocean biodiversity.

“The blob is documented to have caused major loss of marine life, from phytoplankton to zooplankton to fish - including a 100 million cod – to marine animals, such as whales,” said Kevin Trenberth, co-author and senior scientist at the National Centre for Atmospheric Research in the United States. “These manifestations of global warming have major consequences.”

Researchers also warned hot spots in the oceans could have significant effects in storms – such as the heat in the Gulf of Mexico that helped to spawn Hurricane Harvey in 2017 and Hurricane Florence in 2018, which both killed dozens of people.

“The price we pay is the reduction of ocean-dissolved oxygen, the harmed marine lives, strengthening storms and reduced fisheries and ocean-related economies,” Mr Cheng said. “However, the more we reduce greenhouse gasses, the less the ocean will warm. Reduce, reuse and recycle and transferring to a clean energy society are still the major way forward.”

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