Global Warming: The Conveyer Slows

I wanted to know more about the Gulf Stream, and so went to, which informed me that this warm, slow-moving current was first described by Spanish explorer Ponce de Leon in 1513. “The Gulf Stream originates in the Gulf of Mexico and, as the Florida Current, passes through the Straits of Florida and along the coast of the southeastern United States with a breadth of 50 miles. North of Cape Hatteras, it is separated from the coast by a narrow southern extension of the cold Labrador Current and flows northeast into the Atlantic Ocean. Where the warm surface waters of the Gulf Stream meet the cold winds accompanying the Labrador Current, one of the densest concentrations of fog in the world occurs.

The Gulf Stream can be seen (red) in this thermal satellite image.© NOAA

“Parts of the Gulf Stream current are diverted southeast, forming the Canary Currents, which carry cooler waters to the Iberian peninsula and northwestern Africa. An ensuing current, known as the North Atlantic Drift, flows northwest and provides temperate, relatively warm waters to Western Europe. The Gulf Stream has an average speed of four miles per hour but slows down as it widens to the north. At the beginning of the Gulf Stream, the water temperature is 80° Fahrenheit; the temperature decreases as the current moves north.”

OK, now imagine what would happen if this wide, warm flow of water were to slow down or even stop. Ice ages are made of the kind of temperature drop that would be expected if the Earth lost one of its key circulatory systems. In the 2004 book Feeling the Heat, I reported that this process has continued unabated since the last Ice Age, “but global warming is throwing in a monkey wrench by melting ice in the Arctic Ocean. A UN assessment says Arctic sea ice in summertime could diminish 60 percent by 2050. This fresh water could dilute the salinity of the Gulf Stream, which would mean that it would no longer sink to the bottom of the ocean near Iceland and begin its return trip to the Pacific. According to Robert Gagosian, director of the Woods Hole Oceanographic Institute, ‘We’re seeing huge freshening in the North Atlantic. The sinking of the cold, salty water has slowed 20 percent in the last 30 years.’”

And now the news. The online edition of the Times of London reported May 8 that the Gulf Stream slowdown is no longer theoretical, but is already occurring. Peter Wadhams, a professor of ocean physics at Cambridge University, visited the Arctic ice cap on Royal Navy submarines and discovered “that one of the ‘engines’ driving the Gulf Stream—the sinking of supercooled water in the Greenland Sea—has weakened to less than a quarter of its former strength. The weakening, apparently caused by global warming, could herald big changes in the current over the next few years or decades. Paradoxically, it could lead to Britain and northwestern Europe undergoing a sharp drop in temperatures.”

Says Wadhams, “Until recently, we would find giant ‘chimneys’ in the sea where columns of cold, dense water were sinking from the surface to the seabed [1.8 miles] below, but now they have almost disappeared. As the water sank, it was replaced by warm water flowing in from the south, which kept the circulation going. If that mechanism is slowing, it will mean less heat reaching Europe.”

Dr. Gagosian says that a shutting down of the Gulf Stream would mean that “average winter temperatures could drop by five degrees Fahrenheit over much of the United States, and by 10 degrees in the northeastern United States and in Europe. That’s enough to send mountain glaciers advancing down from the Alps. To freeze rivers and harbors and bind North Atlantic shipping lanes in ice. To disrupt the operation of ground and air transportation. To cause energy needs to soar exponentially. To force wholesale changes in agricultural practices and fisheries. To change the way we feed our populations. In short, the world, and the world economy, would be drastically different.”

It isn’t some ravingly liberal politician saying this, but one of America’s most distinguished scientists. You can choose to believe the Dr. Gagosians of this world or take sides with the honorable Senator James Inhofe (R-OK), chairman of the Committee on Environment and Public Works. In a 2003 floor speech to the Senate on “The Science of Climate Change,” Inhofe said that “catastrophic global warming is a hoax,” and possibly the greatest hoax “ever perpetrated on the American people.” Last January, he actually revealed one of his prime sources for this conclusion to be
a novel.

“I highly recommend Michael Crichton’s State of Fear to all of my colleagues,” he said, once again on the Senate floor. “Dr. Crichton, a medical doctor and scientist [!], very cleverly weaves a compelling presentation of the scientific facts of climate change—with ample footnotes and documentation throughout—into a gripping plot. From what I can gather, Dr. Crichton’s book is designed to bring some sanity to the global warming debate.” But can a novel really be said to be part of the global warming debate? David B. Sandalow, an environmental scholar at the Brookings Institute, doesn’t think so. “If [Crichton] has something serious to say on the science of climate change, he should say so in a work of nonfiction and submit his work for peer review. The result could be instructive—for him and us all.”

I don’t want to put words into the distinguished Senator’s mouth, but perhaps instead of invoking fiction in place of scientific evidence he should look at ancient history. He could cite the respected Columbia Earth Institute in claiming, for instance, that the Gulf Stream has slowed down in the past without benefit of human-induced global warming. In Nature magazine, the journal of scientific record, Lamont-Doherty Earth Observatory geochemist Jean Lynch-Stieglitz presented evidence that the Gulf Stream “operated at about two-thirds its current rate during the height of the last ice age. This in turn suggests that the entire oceanic conveyor also slowed, and so moved less heat into the icy upper latitudes.”

Wallace Broecker, senior Lamont-Doherty geochemist and a founding father of the conveyor model of ocean circulation, comments, “Jean’s work suggests that conveyor circulation virtually stopped during the last glacial maximum.” So what’s happening today is not unprecedented, but that may be beside the point. Humans had no effect on the last ice age, but they are a huge factor in the loss of ocean circulation being measured today by scientists like Peter Wadhams, who deserves the last word here:

“One of the frightening things in the film The Day After Tomorrow showed how the circulation in the Atlantic Ocean is upset because the sinking of cold water in the north Atlantic suddenly stops. The sinking is stopping, albeit much more slowly than in the film—over years rather than a few days. If it continues, the effect will be to cool the climate of northern Europe.”

Unlike the good Senator and his novel, I would not cite The Day After Tomorrow as scientific evidence. It’s a popcorn movie, with some basis in science, that puts global cooling on the kind of fast-track timetable that Hollywood demands. Of course, as the Times notes, global cooling might not be all bad. A possible effect is that Europe stays r

elatively cool as the rest of the world burns up. And wouldn’t that irritate the Francophobes in the Congress, presumably including Senator Inhofe?