The Heat Is Online

Gulf Stream Shift Removed From Scientific Forecasts

Dropping Ice Age scenario, researchers discard Gulf Stream catastrophe scenario

The Associated Press, June 14, 2007

TORSHAVN, Faeroe Islands: From the deck of a research ship moored in these gusty north Atlantic islands, workers are offloading three bright orange buoys whose sonar devices will help Bogi Hansen fill more gaps in an intriguing twist on climate change forecasts.

For the past year, the Faeroese scientist's sonar has been pinging the Gulf Stream, the warm ocean current that has kept this subpolar archipelago unfrozen for centuries. His findings are of big interest because they contradict one of the most catastrophic predictions linked to global warming: that Arctic melting will strangle the Gulf Stream, thrusting Europe into a new Ice Age.

In fact, Hansen's research and recent climate models raise a tantalizing possibility: Can the slight weakening of the Gulf Stream expected over the next century actually help to offset the effects of global warming in northern Europe?

Some scientists think so.

"We will benefit a little bit from this," said Helge Drange, of the Nansen Environmental and Remote Sensing Center in Bergen, Norway, a researcher who builds climate models. "Instead of warming of 3-4 degrees C (5-7 F), we may get 2-3 degrees C (4-5 F) in northwestern Europe."

The U.N.-sponsored Intergovernmental Panel on Climate Change said this year that the global ocean circulation powering the Gulf Stream is likely to slow, but is "very unlikely" to suffer an abrupt change.

No climate models project a complete shutdown of the Gulf Stream, which feeds warm water up the east coast of North America and across the Atlantic Ocean to Europe.

"It's one of the good news things in the climate story," said Andrew Weaver, a Canadian researcher and lead author of a chapter dealing with ocean currents in the IPCC report. "To be perfectly honest, it's difficult to fathom a mechanism that could cause its collapse."

Hansen said his latest measurements on the underwater Greenland-Scotland ridge show no weakening in the North Atlantic Drift, the crucial northward branch of the Gulf Stream.

Scientists expect the flow to taper off in coming decades by up to 50 percent as Greenland's melting ice sheet releases freshwater into the north Atlantic, slowing the main pump that drives what is known as the ocean conveyor belt  the global circulation of currents. It is high salinity that causes Arctic water to sink and generate the energy for the Gulf Stream.

Hansen said current projections show that this process "would mitigate the global warming" rather than cause an abrupt and cataclysmic cooling.

Still, there are plenty of uncertainties.

While northwestern Europe, from Britain to Scandinavia, can expect continued gradual warming, the net effect of climate change and a slower Gulf Stream is harder to predict for north Atlantic islands such as Iceland or the Faeroes, a semiautonomous Danish territory with 50,000 inhabitants.

Here, right in the middle of the North Atlantic Drift, is where the warming effect is most pronounced. The average winter temperature in Torshavn is 3 C (37 F)  about 12 C (22 F) higher than in Anchorage, Alaska, which is on the same latitude.

"The Faeroes would be very much colder but also large areas of this region and the whole Arctic would be very much affected if this flow of heat would weaken considerably," Hansen said.

Even a slight cooling could mean the difference between green and white winters for places like the Faeroes where average winter temperatures are just above freezing.

A slowdown in the circulation could also affect marine life, because it transports oxygen and other substances to the deep ocean.

Researchers also are reconsidering the commonly held view that a drop in north Atlantic salinity was caused by melting Arctic sea ice. The salt level has started recovering since 2000 and scientists now say the fluctuations reflect a natural cycle.

"We now realize that the observed decline in ocean salinity that occurred from 1965-2000 had more to do with the wind patterns and storm tracks than with global warming," said Ruth Curry, an oceanographer at the Woods Hole Oceanographic Institution in Massachusetts.

Nevertheless, climate change is expected to play a bigger role in the next cycle of freshening expected around 2020, because the Greenland ice cap is melting faster, Curry said.

"Will it slow the ocean conveyor? It's possible," said Curry, who is not connected to Hansen's research. "Will it cause the same sort of complete alteration that we know happened 12,000 years ago? No, that's very unlikely."

Even the long-established tenet that Europe owes its mild winters to the Gulf Stream is under scrutiny, most vocally by Richard Seager, a scientist at the Lamont-Doherty Earth Observatory of Columbia University in Palisades, New York.

He calls the Gulf Stream effect a myth, and claims the prevailing wind patterns have a much bigger role in explaining why Europe is several degrees warmer in winter than the equivalent latitudes in North America.


"The amount of warming that the current gives  only about 2-3 degrees over land on either side  is really small compared to the temperature difference between those regions, which is more like 15 to 20 centigrade in winter," he said. "So no one should ever confuse that temperature difference between the two regions as being in any way caused by the movement of heat by the Gulf Stream."


Uncertainty also surrounds future climate predictions, primarily because little is known about how fast the Greenland ice cap will melt, and exactly how that will affect oceanic circulation.

Drange played down the possibility of a massive influx of freshwater disrupting the mechanism that drives ocean circulation.


"There is no indication that this is happening now and we don't expect it will happen in this century," he said.


Faeroese fishermen are less sure. Jogvan Trondarson, a veteran shrimper, said he's seeing more and bigger icebergs off Greenland's eastern coast than 20 years ago, and believes they could be a sign the ice sheet is melting faster.


Off the west coast of the giant island, the sea ice has crept back by 200 kilometers (120 miles), and storms have gotten stronger and more persistent on both sides, he said.


"For me it's facts," said Trondarson, tapping his pen on a rough map of Greenland.



Scientists Back Off Theory of a Colder Europe in a Warming World


The New York Times,  May 15, 2007


OSLO -- Mainstream climatologists who have feared that global warming could have the paradoxical effect of cooling northwestern Europe or even plunging it into a small ice age have stopped worrying about that particular disaster, although it retains a vivid hold on the public imagination.


The idea, which held climate theorists in its icy grip for years, was that the North Atlantic Current, an extension of the Gulf Stream that cuts northeast across the Atlantic Ocean to bathe the high latitudes of Europe with warmish equatorial water, could shut down in a greenhouse world.


Without that warm-water current, Americans on the Eastern Seaboard would most likely feel a chill, but the suffering would be greater in Europe, where major cities lie far to the north. Britain, northern France, the Low Countries, Denmark and Norway could in theory take on Arctic aspects that only a Greenlander could love, even as the rest of the world sweltered.


All that has now been removed from the forecast. Not only is northern Europe warming, but every major climate model produced by scientists worldwide in recent years has also shown that the warming will almost certainly continue.


The concern had previously been that we were close to a threshold where the Atlantic circulation system would stop, said Susan Solomon, a senior scientist at the National Oceanic and Atmospheric Administration. We now believe we are much farther from that threshold, thanks to improved modeling and ocean measurements. The Gulf Stream and the North Atlantic Current are more stable than previously thought.


After consulting 23 climate models, the United Nations Intergovernmental Panel on Climate Change said in February it was very unlikely that the crucial flow of warm water to Europe would stall in this century. The panel did say that the gradual melting of the Greenland ice sheet along with increased precipitation in the far north were likely to weaken the North Atlantic Current by 25 percent through 2100. But the panel added that any cooling effect in Europe would be overwhelmed by a general warming of the atmosphere, a warming that the panel said was under way as a result of rising concentrations of carbon dioxide and other heat-trapping gases.


The bottom line is that the atmosphere is warming up so much that a slowdown of the North Atlantic Current will never be able to cool Europe, said Helge Drange, a professor at the Nansen Environmental and Remote Sensing Center in Bergen, Norway.


Temperate Europe is vulnerable because of its northern perch. The latitude of Britain equals that of frigid Newfoundland. Norway corresponds to the southern half of Greenland. The annual mean temperature difference of 10 to 20 degrees across the North Atlantic (all temperature units shown here are in Fahrenheit) is often entirely attributed to the North Atlantic Current.


But in recent years, climatologists have said prevailing winds and other factors independent of the current are responsible for at least half of the temperature anomaly.


For the European warm-water current to stop altogether, the Greenland ice sheet would have to melt fast enough to create a vast freshwater pool in the North Atlantic. Freshwater dilution on that scale would make the current less dense, preventing its two main strands from sinking south of Iceland and west of Norway as they must before they can double back toward the Equator on the underside of what is often called the Atlantic conveyor belt.


The ocean circulation is a robust feature, and you really need to hit it hard to make it stop, said Eystein Jansen, a paleoclimatologist who directs the Bjerknes Center for Climate Research, also in Bergen. The Greenland ice sheet would not only have to melt, but to dynamically disintegrate on a huge scale across the entire sheet.


The worst imaginable collapse would likely take centuries to play out, he said. Any disruption to the North Atlantic Current  whose volume is 30 times greater than all the rivers in the world combined  would thus occur beyond the time horizon of the United Nations climate panel.


The last big freshwater dilution is thought to have occurred 8,200 years ago, when a huge lake atop the retreating North American ice sheet burst through to the Atlantic. For about 160 years, Dr. Jansen said, Europe experienced a severe chill that today would stress society quite a lot.


If the North Atlantic Current weakened 25 percent this century, fractionally offsetting the effect of global warming, Britain in 2100 would still be about 4 degrees warmer than today, the United Nations panel estimated. In France, the net warming would be 5 degrees and here in Norway a bit more, depending on latitude.


When climate modelers simulate a 50 percent slackening of the North Atlantic Current, they still see a net warming in those countries. It is when they completely switch off the current, as they say nature is disinclined to do, that the European climate cools to a level below that of today.


Scientists at the Hadley Center for Climate Prediction and Research near London found that a shutdown of the North Atlantic Current in 2049 would cause temperatures in most of Britain and Norway to fall from a level several degrees warmer than today to a level 4 or 5 degrees chillier than today. That would be enough to curtail agriculture sharply. France, though, would still be slightly warmer than it is now.


In a 1998 cover article for The Atlantic Monthly titled The Great Climate Flip-flop, William H. Calvin spelled out a worst-case scenario for Atlantic Ocean dynamics and concluded, I hope never to see a failure of the northernmost loop of the North Atlantic Current, because the result would be a population crash that would take much of civilization with it, all within a decade.


In 2004, the makers of the Hollywood blockbuster The Day After Tomorrow imagined the sudden icing over of Manhattan after a disruption in North Atlantic currents. Europes fate was alluded to by the implied flash-freezing of the British royal family in Balmoral Castle.


Preparing for a cold future has never been high on the political agenda. Perhaps understandably, European leaders have been more preoccupied with responding to the 2003 summer heat wave that killed 15,000 people across France and the need for new dike technology to keep the Netherlands from being inundated by rising seas associated with melting ice caps.


Richard Seager, a senior research scientist at the Lamont-Doherty Earth Observatory of Columbia University in Palisades, N.Y., said thatEuropeans should trust what they feel in the air. Britain and western Europe have had one heat wave after another so far this century, Dr. Seager said. Its phenomenal. The idea that anyone is worried about a new ice age I find rather odd.