Tim Radford, science editor
Wednesday March 30, 2005
Guardian

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The human race is living beyond its means. A report backed by
1,360
scientists from 95 countries – some of them world leaders in
their fields –
today warns that the almost two-thirds of the natural machinery
that
supports life on Earth is being degraded by human pressure.

The study contains what its authors call “a stark warning” for
the entire
world. The wetlands, forests, savannahs, estuaries, coastal
fisheries and
other habitats that recycle air, water and nutrients for all
living
creatures are being irretrievably damaged. In effect, one
species is now a
hazard to the other 10 million or so on the planet, and to
itself.

“Human activity is putting such a strain on the natural
functions of Earth
that the ability of the planet’s ecosystems to sustain future
generations
can no longer be taken for granted,” it says.

The report, prepared in Washington under the supervision of a
board chaired
by Robert Watson, the British-born chief scientist at the World
Bank and a
former scientific adviser to the White House, will be launched
today at the
Royal Society in London. It warns that:

Because of human demand for food, fresh water, timber, fibre
and fuel, more
land has been claimed for agriculture in the last 60 years than
in the 18th
and 19th centuries combined.
An estimated 24% of the Earth’s land surface is now cultivated.
Water withdrawals from lakes and rivers has doubled in the last
40 years.
Humans now use between 40% and 50% of all available freshwater
running off
the land.
At least a quarter of all fish stocks are overharvested. In
some areas, the
catch is now less than a hundredth of that before industrial
fishing.
Since 1980, about 35% of mangroves have been lost, 20% of the
world’s coral
reefs have been destroyed and another 20% badly degraded.
Deforestation and other changes could increase the risks of
malaria and
cholera, and open the way for new and so far unknown disease to
emerge.
In 1997, a team of biologists and economists tried to put a
value on the
“business services” provided by nature – the free pollination
of crops, the
air conditioning provided by wild plants, the recycling of
nutrients by the
oceans. They came up with an estimate of $33 trillion, almost
twice the
global gross national product for that year. But after what
today’s report,
Millennium cosystem Assessment, calls “an unprecedented period
of spending
Earth’s natural bounty” it was time to check the accounts.

“That is what this assessment has done, and it is a sobering
statement with
much more red than black on the balance sheet,” the scientists
warn. “In
many cases, it is literally a matter of living on borrowed
time. By using up
supplies of fresh groundwater faster than they can be
recharged, for
example, we are depleting assets at the expense of our
children.”

Flow from rivers has been reduced dramatically. For parts of
the year, the
Yellow River in China, the Nile in Africa and the Colorado in
North America
dry up before they reach the ocean. An estimated 90% of the
total weight of
the ocean’s large predators – tuna, swordfish and sharks – has
disappeared
in recent years. An estimated 12% of bird species, 25% of
mammals and more
than 30% of all amphibians are threatened with extinction
within the next
century. Some of them are threatened by invaders.

The Baltic Sea is now home to 100 creatures from other parts of
the world, a
third of them native to the Great Lakes of America. Conversely,
a third of
the 170 alien species in the Great Lakes are originally from
the Baltic.
Invaders can make dramatic changes: the arrival of the American
comb
jellyfish in the Black Sea led to the destruction of 26
commercially
important stocks of fish. Global warming and climate change,
could make it
increasingly difficult for surviving species to adapt.

A growing proportion of the world lives in cities, exploiting
advanced
technology. But nature, the scientists warn, is not something
to be enjoyed
at the weekend. Conservation of natural spaces is not just a
luxury. “These
are dangerous illusions that ignore the vast benefits of nature
to the lives
of 6 billion people on the planet. We may have distanced
ourselves from
nature, but we rely completely on the services it delivers.”

(supplied by Zathur)