Monday, October 30, 2006

Weakening Ocean Current - New Ice Age?

We are taught in school that the U.K. has the warm climate it does because of the Gulf Stream, a warm current that is part of the Atlantic circulatory system. Without it, it is argued, temperatures here would be similar say to Hamilton (Ontario) in Canada, which are by our standards pretty cold much of the time. Should the Atlantic Conveyor circulation fail, then we may be plunged into an ice-age, covering most of northern Europe. Indeed, there is evidence that part of the current, which is usually 60 times more powerful than the river Amazon came to a halt for 10 days during November 2004. In the film "The Day After Tomorrow" is portrayed a nightmare outcome in which the meridonal current which drives the gulf stream shuts-down, and Europe and North America are plunged into an ice-age overnight. While no scientist believes that such a dramatic change could occur so quickly, there is consensus that a failing of the current over even a few decades could have a profound impact. Warm water brought to European shores from the tropics keeps the temperature as much as 10 degrees C higher than would be the case without it, when the continent would be both much colder and drier.
Researchers are unsure of the cause of the 10 day hiatus, and Professor Harry Bryden of the National Oceanography Centre in Southampton said "we didn't know it could happen". Last year, Prof. Bryden's group reported that the Atlantic circulation has dropped by around 6 million tonnes per second from 1957 to 1998. He predicted that, if the current did not strengthen, it would lead to a 1 degree C drop in the average U.K. temperature during the next decade, while a complete shut-down would cause a cooling of between 4 and 6 degrees over 20 years. The study prompted the (U.K.) Natural Environment Research Council to place a network of 16 underwater stations across the Atlantic, stretching from Florida to north Africa, to determine flow rates and "other variables" at different depths. From these measurements, they conclude that the quantity of warm water flowing northwards has fallen by 30%. Bryden also analysed previously collected data supplied by the U.S. National Oceanic and Atmospheric Administration, and found a similar pattern, which suggests that the 2004 shut-down is not a one-off and that most of the slow-down occurred between 1992 and 1998.
Richard Wood, chief oceanographer at the U.K. Meteorological Office's Hadley Centre for climate change, based in Exeter, says that the Southampton findings leave much that is unexplained. He argues that the changes are so large that there should have been a fall in oceanic heating of Europe by one fifth, which should cool the U.K. and Scandinavia by between 1 and 2 degrees C, yet this has so far not been seen. Though unseasonably cold weather in October 2005 briefly covered parts of the U.K. in snow, average European temperatures have been rising. Measurements of surface temperatures in the North Atlantic indicate there was a strong warming trend during the 1990's, which has now halted. Bryden speculates that the warming may have been part of a global temperature increase from human caused greenhouse warming, which is now being offset by the fall in the northerly flow of warm water.
Once the water has warmed Europe, its flow ends at Greenland where it sinks to the ocean floor and then returns south. This is a consequence of the higher salinity of the water once it arrives at the northern regions, due to evaporation and the separation of pure water as ice, hence giving it a greater density so that it sinks. The picture is more complicated however, since Bryden's study indicates that while one area of water on the Canadian side of Greenland seems to be sinking normally, there is a second area on the European side which has partially shut-down so that only half the normal volume of water is sinking and returning south from there. While no one is certain why this has happened, possible causes are a dilution of Arctic waters by melting sea ice or an increased outflow from Siberian rivers hindering it from sinking and returning south. Both effects could be linked to global warming. Some models predict that there will be a shut-down later this century.
There are more uncertainties than there are answers, but the question inevitably arises: can we expect a much colder climate in the ensuing decades, and should we begin stockpiling fuel for that eventuality? Given there is already an acute and amply documented pressure placed on securing fuel supplies as things stand, the prospect of a colder climate hones these imperatives more acutely still. Even if a full "ice age" is still some distance off, we can reasonably expect that maintaining our current standard of life in colder lands will demand more energy, needing us to accrue more fuel just to maintain pace. I believe that the "peak" in material human "progress" may be in sight. Perhaps it is humans who will begin to move to warmer southern climes, even if the Atlantic currents no longer do.

1 comment:

Bobby said...

Very nice article. I agree with most of your evaluation. The timing mechanism could be argued. Thanks for the read.

Bobby Cook