The so-called "greenhouse effect" has caused a glacier on an island near Antarctica to recede, baring rock formations that were buried 26 feet under ice just 28 years ago, a British scientist reported Tuesday.

But Ron Lewis Smith said at a scientific symposium that it was wrong to predict the instant melting of polar ice caps, the Sydney Morning Herald newspaper reported on the conference Monday in Hobart, Tasmania.

"We are really talking about a millimeter rise in the sea level per decade and, to see a substantial effect, we are talking in many centuries," said Smith, head of the Terrestrial Ecology at the British Antarctic Survey.