Science: Update

TWO ANTARCTIC ice shelves have broken up more quickly than anyone had predicted, thus indicating that the effects of global warming may be accelerating, British and American scientists have warned.

Unusually, the team from the British Antarctic Survey and the University of Colorado were so alarmed by their findings that they chose to announce them ahead of publication in the Journal of Glaciology, to which they have been submitted.

The satellite images show the Larsen B and Wilkins ice shelves in "full retreat", having lost nearly 3,000 square kilometres (1,170 sq miles) of their total area in the past year. The images can be viewed at: www.nsidc.colorado.edu/NSIDC/ICESHELVES/lars- wilk-news. Ted Scambos of the University of Colorado said his team had predicted the break-up would happen, but not this quickly.

"It happened much faster than we thought," he said. "It was nearly as much activity in a single year as we've seen, on average, in 10 or 15 years up to now." The Larsen Ice Shelf is on the eastern half of the peninsula, pointing towards Argentina. The Wilkins is on the south-west side.

"Within a few years, much of the Wilkins ice shelf is likely to be gone," said David Vaughan of the British Antarctic Survey.

AMERICAN NEUROLOGISTS think they have found a key enzyme that triggers the onset of Alzheimer's disease. Called presenilin, it may be key to controlling the production of toxic build-ups of insoluble "amyloid beta" proteins, which form tangled webs in the brain. The work, published in Nature, means scientists are "very much on the road" to an Alzheimer's treatment, said Dr Dennis Selkoe, a neurologist at Brigham and Women's Hospital in Boston, who believes that drugs which block the enzyme could be in human clinical trials within three years.

But other scientists cast doubt on whether presenilin is the whole story, and also on whether it acts alone or in concert with other enzymes, so far unidentified. They also pointed out that the enzyme may be important for regulation of other processes such as the immune system, and that degrading its function could lead to unwanted and unexpected side-effects.