It’s one of the most oft-used arguments put forth by climate deniers: that there has been “no global warming” for the last 17 years, as evidenced by a supposed lack of increase in global average surface temperature.
It’s also one of the most oft-debunked, as overwhelming evidence has shown that most of the heat generated from increased carbon emissions gets absorbed into the ocean, not into the atmosphere. What’s more, scientists believe global temperatures are set to rise rapidly in the face of our increasingly warm and acidic oceans.
Still, the idea that warming has been absorbed more and more by the ocean and not as much by the atmosphere has presented a good question for scientists: Why? Why, even as greenhouse gases have continued to concentrate in our atmosphere, have global air surface temperatures remained somewhat steady for the last several years? And where in the ocean has that heat actually gone?
The answer, according to a study published in the journal Science on Friday, is that much of the heat missing from the atmosphere has been stored deep in the Atlantic Ocean, drawn in by a once slow-moving current that seems to have sped up in the beginning of the 21st century. The sped-up current has been able to pull down heat almost a mile into the ocean, according to the paper’s authors, oceanographer Xianyao Chen of the Ocean University of China and atmospheric scientist Ka-Kit Tung of the University of Washington.
Because of the sped-up current, Chen and Tung say that the North and South Atlantic oceans have been storing more energy than the rest of the world’s oceans combined since the year 2000.
“We found the missing heat,” Chen said, according to a research article published alongside the study in Science.
The study does note that changes in the current of the Atlantic Ocean have always happened, and have always affected the temperature of the earth. Before global warming was a factor, though, the changes used to even things out — 30 warm years, followed by 30 cooler years, and so on.
But now that global warming is a factor, the warming looks more “like a staircase,” as Phys.org’s report on the study notes. So, now the changes in currents cause 30 years of accelerated warming, followed by 30 years of no change, followed by 30 more years of accelerated warming, et cetera.
To make their conclusions, Chen and Tung analyzed the overall heat content of oceans across the world since 1970 by looking at ocean temperature and salinity measurements taken from floats, buoys, and ships. The temperature and salinity data was taken at 24 different depths from the surface of the ocean down to 1500 meters. They found the most heat in the Atlantic — challenging other research that has argued the Pacific Ocean was the culprit for the missing heat.
Either way, heat is being stored somewhere in the ocean. And while Chen and Tung say the so-called global warming “hiatus” looks to continue for the next 10 or so years, they also note that the world will “inevitably” switch back to rapid warming in the atmosphere when the current cycle switches. And either way, it also affirms that the heat content of the ocean is still growing — debunking the argument that global warming is taking a “hiatus.”
“The next El Niño, when it occurs in a year or so, may temporarily interrupt the hiatus, but, because the planetary heat sinks in the Atlantic and the Southern Oceans remain intact, the hiatus should continue on a decadal time scale,” the paper concludes. “When the internal variability that is responsible for the current hiatus switches sign, as it inevitably will, another episode of accelerated global warming should ensue.”