New Scientist
April 2, 2005


By Bob Holmes and Duncan Graham-Rowe

Humankind's trampling footprints are becoming ever larger. Our
increasing numbers and quest for more resources are changing and
destroying ecosystems at an unprecedented rate. This will not surprise
ecologists, but the scope and rigour of the Millennium Assessment (MA)
makes the finding harder to ignore than ever.

"There are no surprises - but that's good," says Stuart Pimm, an
ecologist at Duke University in Durham, North Carolina. "It means a
group of people have pulled all the numbers together in a way
thousands of scientists can sign off on."

The most obvious changes are converting natural ecosystems to farmland
and felling forests for lumber and pulp . Forests have been almost
completely eradicated from 25 countries, and in another 29 the area
covered by forest has fallen by more than 90 per cent. Nearly a
quarter of Earth's land surface is now under cultivation, and more
virgin land has fallen to the plough since 1945 than during the entire
18th and 19th centuries combined. The trend has slowed recently
though, and the amount of cropland has actually fallen in Europe and
China, and stabilised in North America.

Nonetheless, the worry is that continued ecosystem degradation will
lead to abrupt changes. Two "ecosystem services" already in the danger
zone are fisheries and supplies of fresh water. According to the
report, these are now so degraded that they are already well beyond
levels that can sustain existing demands, let alone provide for future

Largely as a result of farming, people have greatly altered the flow
of water and nutrients through Earth's ecosystems. Irrigation has
doubled the use of surface water since 1960 and is rapidly reducing
ground water reserves in some arid regions. It is almost 100 years
since synthetic nitrogen fertiliser was first manufactured, and the
world has got through more than half of the total ever used in the
last 20 years.

Crop fertilisation has doubled the availability of nitrogen worldwide
since the mid-19th century and tripled the availability of phosphorus
since 1960. This leads to eutrophication of lakes and rivers and
creates dead zones on the ocean floor due to oxygen depletion. What is
more, deforestation and fossil-fuel burning have boosted CO2 levels in
the atmosphere by about a third since the beginning of the industrial
revolution, with 60 per cent of that rise since 1959.

The most obviously irreversible trend is the loss of biodiversity .
Extinction rates today are perhaps as much as a thousand-fold higher
than the norm throughout evolutionary history. Some 10 to 30 per cent
of the world's land vertebrates are now threatened with extinction.

Copyright 2005