Scientists say the warming of the world’s oceans is accelerating more quickly than previously thought, a finding with dire implications for climate change because almost all of the heat trapped by greenhouse gases ends up stored in oceans.
A new analysis, published Thursday in the journal Science, found that the oceans are heating up 40 percent faster on average than a U.N. panel estimated five years ago. The researchers also concluded that ocean temperatures have broken records for several straight years.
“2018 is going to be the warmest year on record for the Earth’s oceans,” said Zeke Hausfather, an energy systems analyst at independent climate research group Berkeley Earth and an author of the study. “As 2017 was the warmest year, and 2016 was the warmest year.”
As the planet has warmed, the oceans have provided a critical buffer, slowing the effects of climate change by absorbing 93 percent of the heat trapped by human greenhouse gas emissions. But the escalating water temperatures are already killing off marine ecosystems, raising sea levels and making hurricanes more destructive.
As the oceans continue to heat up, those effects will become more catastrophic. Coral reefs will come under increasing stress; a fifth of them have already died in the past three years. Rainier, more powerful storms like Hurricane Harvey in 2017 and Hurricane Florence in 2018 will become more common, and coastlines around the world will flood more frequently.
Because they play such a critical role in global warming, oceans are one of the most important areas of research for climate scientists. Average ocean temperatures are also a consistent way to track the effects of greenhouse gas emissions because they are not influenced much by short-term weather patterns, Hausfather said.
But, historically, understanding ocean temperatures has also been difficult. An authoritative U.N. report, issued in 2014 by the Intergovernmental Panel on Climate Change, presented five different estimates of ocean heat, but they all showed less warming than the levels projected by computer climate models — suggesting that either the ocean heat measurements or the climate models were inaccurate.
Since the early 2000s, scientists have measured ocean heat using a network of drifting floats called Argo. The floats measure the temperature and saltiness of the upper 6,500 feet of the ocean and upload the data via satellites.
But before Argo, researchers relied on expendable bathythermographs, a sort of temperature sensor that ships lowered into the ocean with a copper wire. The wire transferred data from the sensor onto the ship for recording, until the wire broke and the sensor drifted away.
That method was subject to uncertainties that hamper today’s scientists as they stitch together temperature records into a global picture.
In the new analysis, Hausfather and his colleagues assessed three recent studies that better accounted for instrument biases in the historical record. The results converged at an estimate of ocean warming that was higher than the IPCC predicted and more in line with the climate models.