Thu, Dec 18, 2014 - Page 9 News List

Earth faces its sixth ‘great extinction’

Analysis for ‘Nature’ magazine sounds an alarm on the way that human activity — from overfishing to agriculture — is forcing a vast number of species to vanish from the wild

By Robin McKie  /  The Guardian, LONDON

Illustration: Mountain People

A stark depiction of the threat hanging over the world’s mammals, reptiles, amphibians and other forms of life has been published by the prestigious scientific journal Nature. A special analysis carried out by the journal indicates that a staggering 41 percent of all known amphibians on the planet now face extinction, while 26 percent of mammal species and 13 percent of birds are similarly threatened.

Many species are already critically endangered and close to extinction, including the Sumatran elephant, Amur leopard, mountain gorilla and the black rhino. However, also in danger of vanishing from the wild are animals rated as being endangered: bonobos, chimpanzees, bluefin tuna and loggerhead turtles, for example.

In each case, the finger of blame points directly at human activities. The continuing spread of agriculture is destroying millions of hectares of wild habitats every year, leaving animals without homes, while the introduction of invasive species, often helped by humans, is also devastating native populations. At the same time, pollution and overfishing are destroying marine ecosystems.

“Habitat destruction, pollution or overfishing either kills off wild creatures and plants, or leaves them badly weakened,” said Derek Tittensor, a marine ecologist at the World Conservation Monitoring Centre in Cambridge, England. “The trouble is that — in coming decades — the additional threat of worsening climate change will become more and more pronounced and could then kill off these survivors.”

The problem is exacerbated because of the huge gaps in scientists’ knowledge about the planet’s biodiversity. Estimates of the total number of extant species of animals, plants and fungi vary from 2 million to 50 million, according to Nature. In addition, estimates of current rates of species disappearances vary from 500 to 36,000 per year.

“That is the real problem we face,” Tittensor said. “The scale of uncertainty is huge.”

However, the data indicate that the world is heading inexorably toward a mass extinction — which is defined as one involving a loss of 75 percent of species or more. This could arrive in less than 100 years or it could take 1,000 years, depending on extinction rates.

The planet has gone through just five previous great extinctions, all caused by geological or astronomical events. The Cretaceous-Jurassic extinction that wiped out the dinosaurs about 65 million years ago was triggered by an asteroid striking Earth, for example. However, the coming great extinction would be the work of Homo sapiens.

“In the case of land extinctions, it is the spread of agriculture that has been the main driver,” Tittensor said. “By contrast, it has been the over-exploitation of resources — overfishing — that has affected sea life.”

On top of these effects, rising global temperatures threaten to destroy habitats and kill off more creatures.

This change in climate has been triggered by increasing emissions — from factories and power plants — of carbon dioxide, a gas that is also being dissolved in the oceans. As a result, seas are becoming increasingly acidic and hostile to sensitive habitats.

One-third of all coral reefs, which support more lifeforms than any other ecosystem on Earth, have already been lost in the past few decades, and many marine experts believe that all coral reefs could end up being wiped out before the end of the century.

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