Picture: ISTOCK
Picture: ISTOCK

Paris — The world’s oceans have absorbed 60% more heat than previously thought over the past quarter of a century, scientists said on Thursday, leaving the 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.

According to their most recent assessment this month, scientists from the Inter-governmental 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 found that for each of the past 25 years, oceans absorbed heat energy equivalent to 150 times the amount of electricity mankind produces annually. This is 60% higher than indicated in previous studies.

Whereas those earlier studies relied on tallying the excess heat produced by known man-made greenhouse gas emissions, a team of US-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 10m deep,” said Laure Resplandy, assistant professor of geosciences at Princeton and lead study author. “Our data shows that it would have warmed by 6.5ºC  every decade since 1991.”

This compares with an IPCC estimate of a 4°C rise each decade.

Resplandy said the data shows 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, a geophysicist at the University of California-San Diego and co-author of the study.

The IPCC warns that drastic measures are needed to limit global warming to 1.5°C by the end of the century, but the world produced a record amount of carbon emissions in 2017.