British Association for the Advancement of Science: Higher Atlantic waves puzzle researchers

THE North Atlantic has become dramatically rougher over the past 30 years, with waves increasing in height by 30 per cent over the period, writes Tom Wilkie.

But, according to Sheldon Bacon, a scientist with the Natural Environment Research Council, it is a real puzzle. Winds had not increased and it was usually wind speed that drove waves, he said.

Other scientists from the council warned that if global warming truly set in, then Hurricane Andrew could be a harbinger of worse to come. The greenhouse effect would increase the sea surface temperature from which hurricanes derived their power. The result, according to Trevor Guymer, from the council's Centre for Ocean Circulation, would be increased hurricane activity. It was possible there would be more hurricanes, or that they would be more intense. Global warming could result in the hurricane belt moving northwards.

Mr Bacon said he believed the rougher waves in the North Atlantic resulted from changes in the atmosphere: in particular in the differential between low pressure centred near Iceland, and an area of high pressure near the Azores. The pressure gradient between the two areas had got steeper over the past 30 years in a way that correlated with the increase in wave height.

The pressure gradient measured not only wind speed but also its direction and it could be, Mr Bacon suggested, that the winds had been blowing more persistently in one direction, raising higher waves, rather than blowing more strongly but frequently changing direction, which does not give waves a chance to grow. But Mr Bacon warned that this was 'only a quarter of an explanation' and that there were too few measurements of wave height to distinguish between natural variability and climatic change.