Climate scientist author: “Every week there’s a new explanation of the hiatus”
According to a new paper published today in Science, Trenberth's "missing heat" is really hiding in the deep Atlantic, not the deep Pacific as Trenberth claims. See Dr. Judith Curry's take on this today at her blog, and choice quotes:
"In the absence of a convincing explanation for warming since the mid 19th century, as well as the multi-decade hiatus periods, I find the [IPCC] extremely likely confidence level to be logically insupportable."Regarding the anthropogenic aerosol forcing argument mentioned by Dr. Curry, that also appears to be blown out of the water by a paper published today in JGR-Atmospheres:
"JC message to Gavin Schmidt (as per our discussion on Dan Kahan’s blog): No I am not making things up re the 50-50 attribution argument. I regard it as a fundamental flaw in logic to infer high confidence in attribution since 1950, without understanding the warming in the early part of the 20th century and the mid century hiatus."
New paper finds changes in cloud cover caused global brightening & dimming, not man-made aerosols
Thus, very recently published papers point to a combination of natural ocean oscillations, natural changes in cloud cover, and changes in solar activity fully explaining the natural warming since the Little Ice Age, not man-made CO2 nor man-made aerosols.
Following rapid warming in the late 20th century, this century has so far seen surprisingly little increase in the average temperature at the Earth’s surface. At first this was a blip, then a trend, then a puzzle for the climate science community.
More than a dozen theories have now been proposed for the so-called global warming hiatus, ranging from air pollution to volcanoes to sunspots. New research from the University of Washington shows that the heat absent from the surface is plunging deep in the north and south Atlantic Ocean, and is part of a naturally occurring cycle. The study is published Aug. 22 in Science.
Subsurface warming in the ocean explains why global average air temperatures have flatlined since 1999, despite greenhouse gases trapping more solar heat at the Earth’s surface.
“Every week there’s a new explanation of the hiatus,” said corresponding author Ka-Kit Tung, a UW professor of applied mathematics and adjunct faculty member in atmospheric sciences. “Many of the earlier papers had necessarily focused on symptoms at the surface of the Earth, where we see many different and related phenomena. We looked at observations in the ocean to try to find the underlying cause.”
The results show that a slow-moving current in the Atlantic, which carries heat between the two poles, sped up earlier this century to draw heat down almost a mile (1,500 meters). Most of the previous studies focused on shorter-term variability or particles that could block incoming sunlight, but they could not explain the massive amount of heat missing for more than a decade.
“The finding is a surprise, since the current theories had pointed to the Pacific Ocean as the culprit for hiding heat,” Tung said. “But the data are quite convincing and they show otherwise.”
Tung and co-author Xianyao Chen of the Ocean University of China, who was a UW visiting professor last year, used recent observations of deep-sea temperatures from Argo floats that sample the water down to 6,500 feet (2,000 meters) depth. The data show an increase in heat sinking around 1999, when the rapid warming of the 20th century stopped.
“There are recurrent cycles that are salinity-driven that can store heat deep in the Atlantic and Southern oceans,” Tung said. “After 30 years of rapid warming in the warm phase, now it’s time for the cool phase.”
Rapid warming in the last three decades of the 20th century, they found, was roughly half due to global warming and half to the natural Atlantic Ocean cycle that kept more heat near the surface. When observations show the ocean cycle flipped, around the year 2000, the current began to draw heat deeper into the ocean, working to counteract human-driven warming.
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| (Top) Global average surface temperatures, where black dots are yearly averages. Two flat periods (hiatus) are separated by rapid warming from 1976-1999. (Middle) Observations of heat content, compared to the average, in the north Atlantic Ocean. (Bottom) Salinity of the seawater in the same part of the Atlantic. Higher salinity is seen to coincide with more ocean heat storage. |
The cycle starts when saltier, denser water at the surface northern part of the Atlantic, near Iceland, causes the water to sink. This changes the speed of the huge current in the Atlantic Ocean that circulates heat throughout the planet.
“When it’s heavy water on top of light water, it just plunges very fast and takes heat with it,” Tung said. Recent observations at the surface in the North Atlantic show record-high saltiness, Tung said, while at the same time, deeper water in the North Atlantic shows increasing amounts of heat.
The authors dug up historical data to show that the cooling in the three decades between 1945 to 1975 – which caused people to worry about the start of an Ice Age – was during a cooling phase. (It was thought to be caused by air pollution [debunked].) Earlier records in Central England show the 40- to 70-year cycle goes back centuries, and other records show it has existed for millennia.
Changes in Atlantic Ocean circulation historically meant roughly 30 warmer years followed by 30 cooler years. Now that it is happening on top of global warming, however, the trend looks more like a staircase.
The temperature oscillations have a natural switch. During the warm period, faster currents cause more tropical water to travel to the North Atlantic, warming both the surface and the deep water. At the surface this warming melts ice. This eventually makes the surface water there less dense and after a few decades puts the brakes on the circulation, setting off a 30-year cooling phase.
This explanation implies that the current slowdown in global warming could last for another decade, or longer, and then rapid warming will return [read Dr. Curry's opinion on this controversial statement]. But Tung emphasizes it’s hard to predict what will happen next.
A pool of freshwater from melting ice, now sitting in the Arctic Ocean, could overflow into the North Atlantic to upset the cycle.
“We are not talking about a normal situation because there are so many other things happening due to climate change,” Tung said.
Related: Bob Tisdale also debunks
I like the imaginative way they constructed a "prior hiatus" from 1950 through about 1975. Who knew?
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