The world's oceans have absorbed 60% more heat than previously thought over the last quarter of a century, leaving Earth more sensitive still to the effects of climate change.
Oceans cover more than two-thirds of the planet's surface and play a vital role in sustaining life on Earth. According to a recent assessment, scientists from the Intergovernmental Panel on Climate Change (IPCC) say the world's oceans have absorbed 90% of the temperature rise caused by man-made carbon emissions. But new research published in the journal Nature used a novel method of measuring ocean temperature.
It was found that for each of the last 25 years, oceans have absorbed heat energy equivalent to 150 times the amount of electricity mankind produces annually. Whereas those studies relied on tallying the excess heat produced by known man-made greenhouse gas emissions, a team of U.S.-based scientists focused on two gases found naturally in the atmosphere: oxygen and carbon dioxide. Both gases are soluble in water, but the rate at which water absorbs them decreases as it warms.
By measuring atmospheric oxygen and carbon dioxide for each year, scientists were able to more accurately estimate how much heat oceans had absorbed on a global scale.
"Imagine if the ocean was only 30 feet deep," said Laure Resplandy, assistant professor of geosciences at Princeton and lead study author. "Our data show that it would have warmed by 6.5 degrees Celsius every decade since 1991." That compares with an IPCC estimate of a 4.0 degrees Celsius rise each decade. Resplandy said that the data showed mankind must once again revise down its carbon footprint, with emissions needing to fall 25% compared to previous estimates.
"The result significantly increases the confidence we can place in estimates of ocean warming and therefore helps reduce uncertainty," said Ralph Keeling, Geophysicist at the University of California-San Diego and co-author of the study.
The IPCC warns that drastic measures need to be taken in order to live with a global warming of 1.5 degrees Celsius by the end of the century; the world produced a record amount of carbon emissions in 2017.