The paper’s author, Laure Resplandy, from Princeton University, said she and her colleagues found that the oceans had absorbed significantly more heat over the past 25 years than had been estimated in a landmark 2014 report from the United Nations Intergovernmental Panel on Climate Change (IPCC).
“Imagine if the ocean was only 30 feet deep,” said Resplandy, in a news release from the Princeton Environmental Institute that accompanied the study. “Our data show that it would have warmed by 6.5 degrees Celsius (11.7 degrees Fahrenheit) every decade since 1991. In comparison, the estimate of the last IPCC assessment report would correspond to a warming of only 4 degrees Celsius (7.2 degrees Fahrenheit) every decade.”
The findings come weeks after a dire report from the United Nations warned that humanity has just over 10 years to act to avoid disastrous levels of global warming, urging governments to make “rapid, far-reaching and unprecedented changes in all aspects of society.”
The UN report found that the planet will reach the crucial threshold of 1.5 degrees Celsius above pre-industrial levels by as early as 2030, precipitating the risk of extreme drought, wildfires, floods and food shortages for hundreds of millions of people.
The study by Resplandy and fellow scientists at Scripps Institution of Oceanography at the University of California San Diego and Princeton University is significant because it shows the Earth’s climate on the whole is probably retaining more heat than previously thought.
Part of the big question in estimating how much the planet will warm in the future is understanding how sensitive the planet is to carbon emissions, said CNN meteorologist Brandon Miller.
This study reveals that a lot of the heat that was thought to be escaping to space is actually being absorbed in the ocean — and means the planet is more sensitive to carbon emissions than was thought, he said.
As a result, estimates for sea level rise, sea ice melting and coral reefs dying are likely going to be on the worse ends of the ranges scientists thought were possible. If oceans rise faster than forecast, that represents more of an immediate threat to low-lying communities.
The UN report used the old assumptions for heat absorbed in the ocean, Miller added. If further research corroborates the findings of the latest study, those calculations would need to be redone and the forecast would be more dire.
Oxygen, carbon dioxide measured
The researchers found that the oceans have taken in 13 zettajoules of heat energy each year between 1991 and 2016. That’s believed to be 150 times the amount of energy humans produce as electricity annually, according to the Princeton news release.
A zettajoule is 1,000,000,000,000,000,000,000 joules. To put that in context, a 100-watt light bulb emits 100 joules per second.
Rather than using temperature-based estimates from a network of drifting floats, with complete data going back only to 2007, the researchers used precise measurements of atmospheric oxygen and carbon dioxide between 1991 and 2016 to produce an independent estimate of ocean heat uptake over that period.
This approach relies on the fact that as waters get warmer, they release more carbon dioxide and oxygen into the air. Precise measurements of atmospheric oxygen began in 1991 and carbon dioxide in 1958, allowing the researchers to draw on nearly three decades of data.
The result, the paper’s authors said, “suggests that ocean warming is at the high end of previous estimates, with implications for policy-relevant measurements of the Earth response to climate change, such as climate sensitivity to greenhouse gases and the thermal component of sea-level rise.”
The study was funded by NOAA’s Climate Program Office and the Princeton Environmental Institute.