Last year was the warmest in recorded human history for the world’s oceans, bringing to an end the warmest decade, according to a new analysis.
Writing in the journal Advances in Atmospheric Sciences, an international team of 14 scientists from 11 institutes reports that ocean temperatures in 2019 were about 0.075 degrees Celsius above the 1981-2010 average.
To reach this temperature, they say, the oceans would have taken in 228 Sextillion (that’s 228 with 21 zeroes) Joules of heat.
“To make it easier to understand, I did a calculation,” says lead author Lijing Cheng, from the Institute of Atmospheric Physics (IAP) at the Chinese Academy of Sciences.
“The Hiroshima atom-bomb exploded with an energy of about 63,000,000,000,000 Joules. 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.
“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.”
The Atlantic Ocean and Southern Ocean continued to show a larger warming compared to most of the other basins, the paper says, noting that it “is well-established that the Southern Ocean has taken up most of the global warming heat since 1970…”
For their study, the researchers used data from the US National Oceanic and Atmospheric and the results of analysis using a new method, developed by the IAP, which they say accounts for potentially sparse data and time discrepancies in instruments previously used to measure ocean warmth, especially from the ocean surface to 2000 metres deep.
This new data allowed them to examine trends dating back to the 1950s.
They also compared the 1987 to 2019 data to that from 1955 to 1986 and found that the more recent warming was around 450% that of the earlier warming, reflecting a major increase in the rate of global climate change.
“It is critical to understand how fast things are changing,” says study co-author John Abraham from the University of St Thomas, US.
“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.”
To reinforce that point, the researchers note that since 1970 more than 90% of global warming heat has gone into the oceans, while less than 4% has warmed the atmosphere and land where humans live.
The researchers are now examining how warming impacts oceans beyond temperature, including its effect on water’s buoyancy, which directly affects the distribution of nutrients and heat.
Nick Carne is editor of Cosmos digital and editorial manager for The Royal Institution of Australia.
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