Snap climate change
By Margaret Munro
Thursday, March 03, 2005/Friday, October 04, 2002
A remarkable change in the waters of the North Atlantic has thrown what one leading oceanographer is calling a "curve ball" into thinking that the planet will gradually warm due to greenhouse gases in the atmosphere.
Instead, there is a real possibility that global warming may soon trigger the sudden onset of an ice age that could last hundreds of years.
"In just the past year, we have seen ominous signs that we may be headed toward a potentially dangerous threshold," says Dr. Robert Gagosian, president and director of the Woods Hole Oceanographic Institution in Massachusetts. "If we cross it, Earth's climate could switch gears and jump very rapidly -- not gradually -- into a completely different mode of operation.
Gagosian bases his comments on a growing body of evidence that significant changes are underway in the North Atlantic, threatening the ocean current that moderates temperatures in northern climes. Without it London, which is almost as far north as Edmonton, would have much longer, colder winters. And Prince Edward Island potatoes might become a thing of the past.
Talk that climate change might one day trigger the sudden onset of an ice age is not new. But Gagosian believes there is a new urgency, warning that the changes could occur in our lifetime.
And once the changes start, the cooling could be rapid, reducing temperatures by several degrees Celsius over much of the United States, Canada and Europe within a decade.
Gagosian warns rivers, harbours and shipping lanes would freeze much earlier, and transportation, agriculture and fishing would be disrupted.
"In short, the world, and the world economy, would be drastically different," Gagosian says.
His controversial predictions, which he has been making in speeches and has posted on the Wood Hole Web site, are based largely on information garnered from the North Atlantic, where the water is becoming fresher and sinking more slowly.
Igor Yashayaev, at the federal Bedford Institute of Oceanography in Nova Scotia and his colleagues in Britain, the United States and Germany, have found the entire water column of the Labrador Sea has undergone radical change over the past three to four decades.
Data collected during annual spring trips across the Labrador Sea and in waters between Greenland, Iceland and Europe show the North Atlantic, at depths up to 4,000 metres, has become less salty, especially in the last decade.
Scientists are not sure where all the fresh water is coming from. But they suspect much of it is coming the Arctic, where ice has been melting and thinning at an usually high rate.
Gagosian and his colleagues say the flood of fresh water could shut down the so-called Great Ocean Conveyor, the ocean's main heat-circulating system. It drives the Gulf Stream, which carries heat from the tropics north.
By the time water from the Gulf Stream reaches the Labrador and Greenland seas, it is so cool and dense that it sinks into the deep ocean, creating a void that pulls more warm tropical waters north.
Fresh water is more buoyant and less able to sink. Scientists worry that fresher water flowing into the North Atlantic could slow the Gulf Stream or push it south. Or, even worse, shut the conveyor system down completely.
Already, surface water in the Greenland Sea is sinking 20% more slowly that in the 1970s, according to evidence gathered by European scientists. This decreased salinity "is arguably the biggest and most dramatic change in ocean property that has ever been measured in the global ocean," Gagosian says.
"At what per cent will the Ocean Conveyor stop? 25%? 40%? 60%? This is not like a dimmer switch, but more like a light switch. It probably goes from 'on' to 'off,' " he says.
Not everyone, however, is so sure the conveyor is in danger.
"The jury is still out," says Eddy Carmack, an oceanographer at the federal Institute of Ocean Sciences in Sidney, B.C., who is studying changes in the polar and subpolar seas. He is not convinced freshening in the North Atlantic will lead to an abrupt climate change.
"But the stakes are so high, it can not be dismissed," he adds. One thing that can be said with certainty is that the climate is becoming less predictable.
Allyn Clarke, a senior scientist at the Bedford Institute, also cautions against reading too much into the data. He heads the Canadian team that monitors the Labrador Sea.
He says the evidence of freshening in the deep waters of the North Atlantic has been "shocking" to many oceanographers. But like Carmack, he says not enough is known to predict if and when the ocean conveyor could stop. But he says it is a possibility, and one that could trigger an ice age.
Clarke is not as outspoken as his U.S. colleagues, but he says he is in "full sympathy" with Gagosian's report, which stresses the need for better understanding of the changing oceans.
"We are presently doing a global experiment on our climate system with little understanding of which of a number of possible outcomes will result," Clarke says.
Changes in ocean temperatures have been linked to ice ages in the past. About 12,800 years ago, North Atlantic waters cooled dramatically and so did the North Atlantic region.
It took only about a decade to move into a cold spell that lasted close to 1,300 years, Gagosian says.
The most recent shutdown in the North Atlantic circulation is believed to have occurred 500 years ago, wiping out established Norse settlements and vineyards that once thrived in Greenland, he says.
A recent U.S. National Academy of Sciences report, entitled "Abrupt Climate Change: Inevitable Surprises," notes that climate changes have occurred with "startling speed" in the past. And next time, the report said, the cost to agriculture alone could be in the $100- to $250-billion range.
Perhaps the most sobering realization is there will be little anyone can do about it -- short of adapt.
"The climate system can and has moved to new climate states in a matter of decades," Clarke says. "If the system undergoes such a change, we have virtually no idea of how to attempt to stop or reverse the system."