11.50am - by STEVE CONNOR
LONDON - Planet Earth is going through its sixth and probably its most devastating period of mass extinction with scores, and possibly hundreds of species of animals and plants dying out each year.
Unlike the previous five extinction waves, however, this time the culprit is just one other lifeform – Homo sapiens.
A major United Nations report on the environment to be published this week will highlight the scale of a problem that many conservationists believe is set to get rapidly worse over the next 30 years as wildlife "hotspots" are either destroyed or invaded by a less diverse range of species.
Some scientists estimate that the "sixth wave" of mass extinction is between 1,000 and 10,000 times greater than the normal "background" rate at which species are lost naturally.
Such a dramatic fall in biological diversity is identified as one of the most pressing problems facing humanity by the scientists who contributed to the Global Environment Outlook-3 (GEO-3) report of the United Nations Environment Programme (UNEP).
The report, to be published tomorrow, will identify a total of 11,046 species of plants and animals that are known to face a high risk of extinction, including 1,130 mammal species (24 per cent of the total) and 1,183 species of birds (12 per cent of the total).
Human activities, from habitat destruction to the introduction of alien species from one area of the world into another, are listed as the major causes of this dramatic loss in biodiversity.
Scientists who contributed to the report also identify some 5,611 species of plants that are known to be on the verge of extinction. They point out that the true figure is likely to be far higher, given that only 4 per cent of the known plant species in the world have been properly evaluated.
The GEO-3 report covers almost every aspect of environmental degradation, from forest destruction to water pollution. It is designed to set the framework for the World Summit on Sustainable Development to be held this summer in Johannesburg.
GEO-3 looks back on the past 30 years of environmental degradation, since the 1972 Stockholm Conference on the Human Environment, in order to assess the likely prospects for the next 30 years.
It is likely to warn that many of the factors that have led to the extinction of species in recent decades continue to operate with "ever-increasing" intensity. Major threats to life on Earth are overexploitation of natural resources, pollution, habitat destruction, the introduction of alien species and global climate change, said the scientists who advised UNEP.
They identify the loss of habitats by human encroachment as one of the most pervasive threats to wildlife. Habitat loss and fragmentation of breeding grounds are behind the precarious predicament of 89 per cent of threatened birds, 83 per cent of threatened mammals and 91 per cent of endangered plants, according to UNEP scientists.
In addition to growing poverty and climate change caused by global warming, UNEP has identified alien invasive species as the second major threat to biodiversity, affecting some 30 per cent of threatened birds and 15 per cent of threatened plants.
The black rat, which since 1800 has stowed away on ships sailing to the remotest corners of the world, is held responsible for the biggest slaughter of birds, especially those living on uninhabited islands.
Another of man's hitchhikers, the crazy ant, has caused havoc to native wildlife from Hawaii to the Seychelles and Zanzibar. The ant, named for its frenetic movements, killed 3 million crabs in 18 months on Christmas Island alone.
A host of other invasive aliens has inflicted enormous environmental and economic damage throughout the world. The list includes the brown tree snake, the small Indian mongoose, the Nile perch, the strawberry guava, the water hyacinth, the zebra mussel and the brushtail possum.
"After habitat loss, this biological invasion constitutes the greatest threat to biodiversity, and it has already had devastating consequences for this planet," said Jeff McNeely, chief scientist at the International Union for Conservation of Nature in Geneva.
Dr McNeely said that the next 30 years could be the defining moment for life on Earth. Either we can finally recognise the problems and do something about them, or we don't, he said.
"I think it could go either way. It could be a golden age of nature conservation, or it could be a disaster scenario. If we assume a doomsday scenario then we're going to live in a greatly oversimplifed world.
"Most of the remaining species are going to be widely dispersed and cosmopolitan. We will have lost many of the large mammals and birds and life in general will be more homogeneous, with a smaller capacity to adapt to a changing environment."
Within the next 30 years, if the biodiversity crisis is not addressed, it is likely that the last tiger, rhino, Asian elephant, cheetah and mountain gorilla will have been lost in the wild, Dr McNeely said.
Yet it is less well known animals and plants that are often at the greatest risk. The Chinese alligator is the most endangered crocodilian in the world, with only 150 individuals remaining in the wild. Half of the world's insect-eating pitcher plants are threatened and one, the green pitcher plant, is critically endangered because of the loss of its wetland habitat.
Scientists have identified and named about 1.5 million species but they believe that between 5m and 15m species have yet to be formally classified. It is now generally assumed that many unnamed animals, plants and micro-organisms are going to become extinct before they are even known to science.
Lord May, the Oxford zoologist, has estimated that the current extinction rates are likely to increase still further over the next century or so.
"This represents a sixth great wave of extinction, fully compatible with the Big Five mass extinctions of the geological past, but different in that it results from the activities of a single other species rather than from external enviromental changes," Lord May said.
Yet this appalling catalogue of extinction is more likely to go unrecorded as fewer scientists are being trained in the field of taxonomy – the science of systematic classification. Last week the House of Lords Select Committee on Science and Technology warned that a shortage of taxonomists and an underfunding of the research centres for systematic biology are jeopardising efforts to protect wildlife.
"We have a cultural and moral obligation, as well as a pragmatic economic need, to record and, as far as possible, conserve the diversity of life with which we share the planet," the select committee said.
* There have been five mass extinctions in geological history, the last occurring about 65m years ago with the extinction of the dinosaurs and the first about 440m years ago, which eliminated some 75 per cent of animals.
* Over the past 500 years, human actitivies are known to have made 816 species extinct in the wild, although the true number is thought to be far higher.
* The total number of animal species officially listed as endangered has grown from 5,205 species in 1996 to 5,435 species today. The total number of endangered animals and plants stands at 11,046.
* Only about 2 to 4 per cent of all the species that have ever lived are still alive today.
* Of the 128 recorded species of extinct birds, 103 are known to have become extinct since 1800. Sixteen species of albatross are threatened now compared to just three in 1996 as a direct result of long-line fishing.
* Beetles are by far the most common group of animals on the planet, and insects in general account for about half of all the animal species.
* Biodiversity "hotspots", known as Vavilov centres, are thought to be responsible for generating the rich diversity of wild plants thought to be important for human crops.By Steve Connor