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For the past 13 years, global surface air temperatures have hardly budged higher despite continual pumping of planet-warming gasses into the atmosphere from the engines of modern life. Does this prove global warming is a giant hoax? No, according to a new study, which says the missing heat is being blown into the western Pacific Ocean by extraordinarily powerful and accelerating trade winds.
"Their acceleration over the last couple of decades is way stronger than you've ever seen in a climate model, about twice as strong," Matthew England, a climate scientist at the University of New South Wales in Sydney, Australia, told NBC News. "This is an unprecedented level of strengthening and it is strong enough that it is actually pushing heat in the Pacific Ocean into the ocean's interior," he added.
As the heat is drawn down into the ocean's interior, cooler water rises to the surface and cools air temperatures. When — it's not a matter of if, noted England — the winds slacken, the heat stored in the Pacific Ocean will return to the atmosphere, allowing the surface air temperatures to spike higher and "catch up to the original projections of global warming in under a decade."
The finding reported Sunday in the journal Nature Climate Change helps the climate science community explain a head-scratcher of a discrepancy between the temperature trends churned out by climate models and those observed in the real world, noted John Fyfe, an expert on the so-called warming hiatus at Environment Canada in Victoria, British Columbia. He was not involved in the new research.
"If you let the models do what they want to do without constraining them by observations, then they will not reproduce the hiatus," he told NBC News. "And they don't do that because ... they do not reproduce this cooling over the past 10 or 20 years in the tropical Pacific. Instead they show, on average, warming."
Building consensusThe new paper is the latest contribution to an ongoing effort to explain the warming hiatus. Other theories range from sunlight blocking particles in the atmosphere to lower activity on the sun. In recent months, several researchers have converged on the idea that the oceans are absorbing much of the missing heat at some depth.
"...if you let the ocean cool, it can have a global effect, and the effect is of a magnitude that is consistent with the current flattened surface temperature curve."
A paper published Aug. 28 in Nature suggested that unusually cool surface temperatures observed in the Pacific Ocean could explain the warming slowdown. The new paper performs a similar calculation, but instead of the cooler waters, England and his colleagues added the intensifying trade winds, which lead to ocean surface cooling.
"They both show that if you let the ocean cool, it can have a global effect, and the effect is of a magnitude that is consistent with the current flattened surface temperature curve," Shang-Ping Xie, a climate scientist at the Scripps Institution of Oceanography in La Jolla, Calif., and a co-author of the Nature paper, told NBC News.
The new study brings clarity to the "sequence of cause and effect," noted Fyfe, "beginning with the trade wind intensifcation, the drawdown of heat into the ocean, meaning cooling at the surface. That has been an advance and very useful in our physical understanding of things."
One of the next questions, noted England, is what causes the trade winds to strengthen.
The answer begins with a poorly understood, multidecade oscillation between warm and cool periods in the Pacific. This mode of variability, he said, appears to underpin whether decades are dominated by the El Niño or La Niña weather patterns. In the cycle's cool phase, as it is in now, trade winds increase.
"That mode in the Pacific can explain about half of the wind trend," England said. What explains the other half, at this point, remains a mystery. Some evidence suggests it could be linked to warming in the Indian Ocean, though the mechanism, he stressed, is unclear. "It is not at all resolved yet why these winds are twice as strong as we would expect just from the oscillation," he said.
The picture is further muddled by the fact that "longer-term climate models have these winds weakening over the 21st century; that is to say 100 years from now they should be weaker. The fact that they have gotten stronger over the past 20 years, I think, is a surprise," England said, adding, "It suggests that there is something that is happening in the real system that is not quite captured in the models."
Model failureThe shortcomings of the climate models highlighted in this new paper feed into larger criticism that the models play down the importance of natural variability in the global climate system. "You want to have enough noise in your system" in order to get a realistic result, noted Xie.
That this shortfall is highlighted in the new research, he added, "is quite a nice result, but in a sense it is bad news for the climate research community because it does point to a potential problem for the climate models."
"The overall big picture that the planet is warming and that that warming is due to human influence stills stands with or without the hiatus."
A problem with the models, in turn, could erode trust in climate science, noted England. But "that would be akin to writing off the medical profession for finding out something new about an illness that they didn't know about earlier," he said.
The inability of the models to capture the observed wind trends and thus the hiatus is "just one small process in the global system that seems to need improvement," he noted. The long-term global warming trend, he added, is independent from decade-to-decade variability in the Pacific Ocean.
Fyfe echoed the sentiment. Instead of undermining climate science, he said, "What you are seeing here in this discussion is the natural evolution of science and improving our understanding. The overall big picture that the planet is warming and that that warming is due to human influence stills stands with or without the hiatus."