The ocean is warming much faster than previously thought, new research has found, suggesting that global climate goals may be even harder to reach.
The new study published yesterday in the journal Nature concluded that the global oceans may be absorbing up to 60 percent more heat since the 1990s than older estimates had found.
Previous estimates from the U.N. Intergovernmental Panel on Climate Change found that the oceans were taking up around 8 zetajoules of energy each year. That’s an “8” followed by a whopping 21 zeros.
The new research, though, put it at around 13 zetajoules. For comparison, total energy consumption around the world is around half a zetajoule annually, according to the International Energy Agency.
This suggests that the Earth, as a whole, is more sensitive to climate change than previous estimates would imply. And that means the planet may respond more strongly to future greenhouse gas emissions than expected.
“For a given level of emissions, the Earth has warmed more than we thought,” said lead study author Laure Resplandy, an ocean and climate expert at Princeton University. “For the same amount of emissions, some of the heat is going into the ocean, so we missed it, kind of.”
This may have some grave implications for global efforts to meet the climate targets outlined under the Paris Agreement. Currently, world nations are striving to keep global temperatures within 2 degrees Celsius of their preindustrial levels, or a more ambitious 1.5 C if possible. Just last month, the IPCC released a much-anticipated report on the 1.5 C threshold, concluding that meeting the target will require an “unprecedented” effort from world leaders and net-zero carbon emissions by 2050.
If the Earth is more sensitive to climate change than previously thought, those temperature targets could approach more quickly. That means nations may have to work harder or cut emissions more quickly to stay on track.
In fact, the study suggests that the maximum amount of emissions humans could still emit without overshooting the Paris targets would need to be reduced by about a quarter.
“If the Earth is actually more sensitive than we thought, it closes the window for those easier pathways,” Resplandy said. “It makes it harder to get to the temperature target, to stay below 1.5 or 2 degrees.”
‘Much-needed independent confirmation’
Scientists know the ocean plays a critical role in the global climate, helping to absorb excess heat from the warming atmosphere. Oceans may store as much as 90 percent of the globe’s extra heat. Exactly how quickly the oceans have been warming, though, has been subject to some debate.
In the past decade, scientists have significantly beefed up a large global network of ocean floats—part of an international program known as “Argo"—that measure temperature and salt content. But before 2007 or so, ocean floats were much more sparse, and scientists also widely relied on measurements taken by passing ships. That made it a little difficult to estimate ocean changes throughout the world, because these data tended to be concentrated mainly in major shipping routes.
Still, multiple studies have attempted to hone global estimates of ocean heat uptake before 2007, often using various statistical methods to evaluate data from ships and floats collected before the Argo network kicked off. The new study isn’t actually the first to suggest that the IPCC’s previous estimates may be too low. In the past few years, other research has also suggested that the oceans may be warming faster—although the exact rate varies from study to study.
Because of the issues with collecting direct ocean data in decades past, the new research attempted to solve the problem without using direct ocean measurements at all. Instead, it relied on measurements of oxygen and carbon dioxide in the atmosphere, dating back to 1991.
There’s a strong relationship between ocean heat and the amount of dissolved gas from the atmosphere that oceans can hold. As the ocean warms, its ability to take in oxygen and carbon dioxide decreases, and more of those gases remain in the atmosphere.
By looking at changes in atmospheric oxygen and carbon dioxide levels—controlling for other factors, like human emissions of greenhouse gases—the scientists were able to estimate how the ocean’s heat content had changed over the last few decades.
“The idea was, can we find an independent way of estimating warming that would give some independent constraint on the ocean warming?” Resplandy said.
The new findings, the authors wrote, provide a “much-needed independent confirmation” of other recent studies suggesting higher rates of ocean warming.
The research only focused on 1991 to the present. If compared with estimates from earlier decades—which do still rely on shipping and float data—the study seems to suggest that the pace of ocean warming has significantly increased in the last few decades.
This is generally in line with other recent research. Another study, published last year in Science Advances, used updated methods to evaluate the older shipping and float data from the 1960s to now. It found that ocean heat uptake has mainly increased since 1990 or so, and that the warming has also crept into deeper and deeper parts of the sea.
John Fasullo of the National Center for Atmospheric Research, one of the co-authors of that study, noted that the new research may provide “a useful corroborating approach” when it comes to the question of ocean heat uptake—another way of looking at the problem and coming to the same conclusion.
Kevin Trenberth of NCAR, another of that study’s co-authors, noted that because the new research constitutes a novel approach, there are some uncertainties that still need to be resolved. But he said the results are generally compatible with those of his own research.
The findings “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),” he told E&E News by email. “The oceans account for about 92% of the Earth’s energy imbalance. This is why we are having increased bouts of strong storms (hurricanes, typhoons) and flooding events.”
While the exact values of ocean heat uptake may be up for debate, more studies are all coming to the same general conclusion—that it’s a bigger problem than scientists previously thought. And that’s something to be taken seriously, the authors say.
“That’s what we want in science,” Resplandy said. “We want to have the same answer by different ways.”
Reprinted from Climatewire with permission from E&E News. E&E provides daily coverage of essential energy and environmental news at www.eenews.net.