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How do you take the temperature of the ocean?
The question may seem to be the prelude to a child's joke. But for climatologists, the answer has serious consequences.
Climate change is rapidly heating up the world's oceans and destroying aquatic organisms – such as coral reefs and kelp forests – that anchor entire ecosystems. Warmer waters also cause sea level rise and make extreme weather events such as hurricanes more destructive.
If scientists can more accurately measure the speed at which the oceans are warming, they can better predict the future effects of climate change. And a study published Wednesday in the journal Nature suggests that the oceans are warming much faster than estimates made by the Intergovernmental Panel on Climate Change, the global organization that provides data climate.
The study, led by Laure Resplandy, a biogeochemical oceanographer at Princeton University, found that between 1991 and 2016, the oceans were warming by an average of 60% more per year than the committee's official estimates.
In October, the panel released a major report predicting some of the worst effects of climate change, including coastal flooding, food shortages and massive coral reef loss. could be realized as early as 2040 if human emissions of greenhouse gases are maintained at current levels. I.P.C.C. The report showed that scientists may underestimate the gravity of the current global climate trajectory.
The new ocean temperature estimates, if accurate, may indicate that global warming in recent decades has exceeded conservative estimates and has been more in line with the worst scenarios envisioned by scientists.
Researchers used a new approach of calculating ocean temperatures by measuring levels of carbon dioxide and oxygen in the atmosphere.
These gases dissolve in oceanic waters, but the amount of water that an ocean can hold depends on its temperature. "The warming of the ocean is essentially causing the elimination of oxygen and carbon dioxide," said David Nicholson, associate scientist at the Woods Hole Oceanographic Institution, who did not participate at the study.
As Dr. Resplandy pointed out, "If you leave a Coca-Cola out in the sun, it will heat up and it will lose gas. It's a bit the same idea. "
Scientists normally measure ocean temperature with the help of thermometers, but assembling a global temperature record requires the use of thermometers around the globe. The global temperature readings were uneven before 2007, when an international consortium launched a program, dubbed Argo, creating an international network of instruments for measuring ocean temperature.
But a group of the Scripps Institution of Oceanography had been doing precise measurements of atmospheric carbon dioxide since 1991, for independent reasons. Dr. Resplandy and her team used this dataset for this study.
Dr. Nicholson said the study showed that data collection could now have unexpected benefits. "This shows the importance of collecting these long-term time series even though it is not clear at first what will be the result," he said. I said.
Scientists already know that the world's oceans absorb 90% of the excess heat trapped on Earth by man's greenhouse gas emissions. In his recent report, I.P.C.C. used one of the lowest available estimates of global warming. Dr. Resplandy and her team found that the higher estimate was more consistent with what was happening.
"Their estimates overlap with previous estimates, but they are aligned with some of the highest estimates," said Dr. Nicholson. "It's not like completely changing our understanding of what the ocean could be. This is a new type of measure that is weighing in the highest part of it. "
There are warnings. This approach is new and it is unclear whether it will withstand further scrutiny. Kevin E. Trenberth, principal investigator in the Climate Analysis section of the National Atmospheric Research Center, said the methodology worked best over long periods but did not detail what was happening each year.
Nevertheless, Dr. Trenberth's own research has revealed that I.P.C.C.C. for the heat of the observed ocean were too low. "This is a new complementary method, and the results are mostly consistent with our estimates," he wrote in an email.
Dr. Resplandy stated that his work did not disrupt the work of I.P.C.C. point out that humanity only has a few decades to counter some of the most catastrophic effects of climate change.
"It does not change the results," she said. "What this does is it makes it harder to get there."
For more information on the climate and the environment, follow @NYTClimate on Twitter.
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