by Axios | 11.2.18
The world's oceans have absorbed about 60% more heat during the past 25 years than previously estimated, according to a new study published in the journal Nature. The study takes advantage of a new method that can serve as a whole ocean thermometer.
Why it matters: If the ocean is absorbing even more heat than observed, it would suggest future global warming will track on the upper end of projections — possibly as high as 5°C, or 9°F, by 2100 if emissions are not significantly curtailed.
The oceans are absorbing about 93% of the extra energy from increasing amounts of greenhouse gases in the atmosphere.
What they did: For the study, scientists, led by Princeton University geochemist Laure Resplandy and Ralph Keeling from the Scripps Institution of Oceanography, devised a new way of taking the global ocean temperature. It relies on precise atmospheric measurements of oxygen and carbon dioxide, which date back to 1991.
What they found: The amount of carbon dioxide that can be emitted by human activities before putting the goals of limiting warming to under 2℃, or 3.6℉, out of reach is about 25% less than what was previously calculated.
“Imagine if the ocean was only 30 feet deep,” said Resplandy in a press release. “Our data shows that it would have warmed by 6.5℃, or 11.7℉, every decade since 1991. In comparison, the estimate of the last IPCC assessment report would correspond to a warming of only 4℃, or 7.2℉, every decade.”
What they're saying: Keeling told Axios the results, “Imply that there’s likely to be more warming in the future.”
"This study shows that estimates of this ocean heat uptake are probably on the high side of what we previously thought," said NASA climate scientist Kate Marvel. "Why is this scary? Because of something called 'climate sensitivity:' a measure of how hot the planet will eventually get."
Pieter Tans, who closely tracks the amount of carbon dioxide in the Earth's atmosphere for NOAA and was not involved in the new study, told Axios the paper is valuable for providing a new, independent estimate of global average ocean warming.
"In case the larger estimate of ocean heat uptake turns out to be true, adaptation to, and mitigation of, our changing climate would become more urgent."
— Pieter Tans, NOAA
However, Tans cautioned that the new estimate is still uncertain, and needs to be replicated by subsequent studies. So too did Kevin Trenberth, a senior scientist at the National Center for Atmospheric Research who was not involved in the new study.
Ultimately, the calculations, Trenberth says, "have implications, because the planet is clearly warming and at faster rates that previously appreciated, and the oceans are the main memory of the climate system (along with ice loss)."
Illustration: Sarah Grillo/Axios
Written by Axios
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