The world’s oceans may be heating up faster than previously thought — meaning the planet could have even less time to avoid catastrophic global warming than predicted just weeks ago by the United Nations’ Intergovernmental Panel on Climate Change.
According to a study published Wednesday in the journal Nature, ocean temperatures have been warming 60% more than outlined by the IPCC.
“The ocean warmed more than we thought, and that has serious implications for future policy,” said Laure Resplandy, a researcher at Princeton University’s Environmental Institute who coauthored the report. “This is definitely something that should and will be taken into account in the next report.”
The new study, authored by scientists at Princeton University, UC San Diego’s Scripps Institution of Oceanography and a number of other research centers around the world, is not the first to suggest oceans could be warmer than previously thought.
The report, however, relies on a novel approach that could revolutionize how scientists measure the ocean’s temperature. The findings would need to be reproduced in coming years to gain widespread acceptance throughout the scientific community.
According to the most recent IPCC report, climate emissions need to be cut by 20% by 2030 and then zeroed out by 2075 to keep warming from exceeding 2 degrees Celsius (3.6 degrees Fahrenheit) above preindustrial levels.
The new report found that emissions levels in coming decades would need to be 25% lower than laid out by the IPCC to keep warming under that 2 degree cap.
That’s because, according to climate scientists, even if the world slams the brakes on greenhouse gases tomorrow, rising ocean temperatures will continue to drive warming for several more decades. If those warming impacts are underestimated, humanity could easily skid past its goals for capping climate change.
“When you stop the greenhouse gases, the ocean continues to warm for like another two decades, and so everything continues to warm,” said Ralph Keeling, climate scientist at Scripps Institution of Oceanography and coauthor of the report. “Extra warming in the pipeline means it’s harder to stay below the climate targets.”
Earth has already warmed by roughly 1 degree Celsius above preindustrial levels and is on track to warm 3 degrees by the end of the century, according to the IPCC.
Scientific consensus has found that the impacts of climate change are being felt today with stronger storms, drought and wildfire.
Even if human emissions are reduced to zero, previously emitted greenhouse gases, such as carbon dioxide, will persist in the atmosphere for hundreds of years before dissipating — locking in some level of climate change for generations to come.
With 2 degrees of warming, the impacts to humanity could be catastrophic, all but wiping out the planet’s coral reefs, triggering severe food shortages and throwing hundreds of millions of people, especially in developing countries, into extreme poverty.
Much of the data on ocean temperatures currently relies on the Argo array — robotic devices that float at different depths, surfacing roughly every 10 days to transmit readings to satellites. There are about 3,800 such pieces of equipment in waters around the globe that provide the publicly available information.
However, the program, which started in 2000, has gaps in coverage. Even with national efforts providing hundreds of new floats a year, some parts of the ocean have too many while others have too few.
“It’s not that easy to reliably estimate the whole ocean heat from spot measurements,” Keeling said. “You have to model what’s happening in the gaps.”
Still, the system’s large number of direct measurements means any individual errors are averaged out, said Pelle Robbins, a researcher with the Massachusetts-based Woods Hole Oceanographic Institution’s department of physical oceanography, who works with the Argo program.
“The power of Argo is that we have so many instruments that we’re not reliant on any one of them,” he said. “When you average over things, you beat down the error.”
By comparison, Resplandy and Keeling calculated heat based on the amount of oxygen and carbon dioxide rising off the ocean. Filling round glass flasks with air from research stations in the Canadian Arctic, Tasmania and La Jolla, San Diego, researchers analyzed the samples to determine the aggregate temperature of the ocean.
Their paper is an extensive effort to prove this new method and ensure the calculations are free of any scientific errors.
Robbins said the new approach is “bold,” but he still believes strongly in the accuracy of the Argo program.
“It’s an intriguing new clue,” he said, “but it’s certainly not the case that this study alone suggests that we have been systematically under-representing the oceanic warming.”
Resplandy said her discovery is not intended to replace the Argo system but rather to complement it. “In science, we want several methods to measure things, to have several methods that converge.”