"An ocean current in the North Atlantic is getting weaker. That may be bad news for north-west Europe"

Read the full article from the Dec 1st 2005 issue of the Economist. (Subscription required.)

"Since 1957, the International Geophysical Year, the south part of the North Atlantic has been studied from time to time by taking measurements along latitude 25°N from the Canary Islands to Florida. This line marks the point where the maximum amount of heat is being shifted around, and is also a place where the separation of the individual currents is easy to follow (seabed features further north tend to break the currents into separate streams).

"Five such transects have been taken, the three most recent being in 1992, 1998 and the one Dr Bryden is reporting, which was done in 2004. Within the usual margins of error, the results in 1992 were the same as those of the earlier two. In 1998, though, the DSRF (Deep Southerly Return Flow) showed an appreciable drop in flow. And in 2004 it had dropped further. The surface flow of the Gulf Stream past Florida, though, was unchanged. And, to complete the equation, the volume carried by the subtropical recirculation had increased to compensate for the drop in the DSRF. The result, when the numbers were crunched, suggests that the volume of water being carried by the Atlantic Conveyor Belt has dropped by 30%.

"If that is correct, and more importantly, if it were sustained, the result for places such as Britain would be a 1°C drop in average temperature—enough to be noticeable. If it were not merely sustained, but got bigger (and the 2004 figure was larger than that for 1998), the temperature drop would be greater. And if the conveyor belt stops altogether, as it has in the past on more than one occasion, Britain's climate would come to resemble that of Newfoundland. The questions, of course, are why is this happening, and can anything be done?"

Sometimes forewarned is not forearmed! It will be quite a while before evidence can be gathered on this phenomenon that will convince the Bush Administration, and it will be much longer until the trends in greenhouse gas emisions that cause global warming can be affected. Let us hope that this the climate of the British Isles is not going to get to be like that of New Foundland. Still, the knowledge that this might happen is valuable!

Moreover, the news demonstrates the wisdom of the "precautionary principle". We know very little about the mechanisms of climate and climate change, and our experience with man-made impacts on global systems is still very limited. While we are shooting in the dark, we better be very careful not to hit anything important!