10. Lost forever: species extinctions continue unchecked

Animals continue to disappear

Of the handful of big environmental issues confronting humanity, few are as disturbing or as emotionally charged as global extinction. The figures are notoriously tentative, but anywhere between 20,000 and 100,000 species a year are believed to be disappearing permanently from the face of the planet. Many plants and animals are thought to become extinct before they are even known to science.

The current rate of extinction is up to 1,000 times the "background" extinction rate--the average rate at which animal and plant species have been disappearing during the last 65 million years. In their book "The Sixth Extinction," Richard Leakey and Roger Lewin warn that by the end of the 21^st century, up to half of the world's species may have vanished for good.

Sadly, this picture is as accurate now as it was 10 years ago. For all the urgency with which the Convention on Biological Diversity was signed, its good intentions have not been matched by effective actions.

The title of Leakey and Lewin's book is a reference to the five major extinctions that are believed to have taken place during the 4.5-billion-year history of life on Earth. The most recent was 65 million years ago, and brought an abrupt end to the age of the dinosaurs.

The principal cause of the mass extinction currently under way is a loss of habitats, and in particular the destruction of species-rich rainforest which is home to as many as half of the world's species. Tropical rainforest is disappearing at the same rate as it was 10 years ago--about one per cent a year.

To make matters worse, the relationship between habitat loss and species extinction is non-linear. Many of the world's biodiversity "hotspots" are the very places where habitats are disappearing most rapidly.

A survey of 400 members of the American Institute of Biological Sciences carried out in 1998, revealed that 70 per cent of them believed a sixth mass extinction was under way. But a drastic loss of species is more than just a problem for biologists. Even the loss of natural species with pharmaceutical or agricultural potential may only be the tip of the iceberg. The loss of species undermines the ability of ecosystems to withstand natural and man-made pressures and regulate processes that keep air and water clean and the planet livable.

If the costs of replacing these services of nature seem high, try to calculate them for the millions of years Norman Myers of Oxford and Andrew Knoll of Harvard University say it will take evolution to replace the biodiversity we already squandered.