The Great Lakes Zephyr - Wind Energy & Hydrogen Journal

Eco-Economy Update 2004-4
For Immediate Release
Copyright Earth Policy Institute 2004
March 2, 2004


THE SIXTH GREAT EXTINCTION:
A Status Report
http://www.earth-policy.org/Updates/Update35.htm

Janet Larsen

Almost 440 million years ago, some 85 percent of marine animal species
were wiped out in the earth's first known mass extinction. Roughly 367
million years ago, once again many species of fish and 70 percent of
marine invertebrates perished in a major extinction event. Then about 245
million years ago, up to 95 percent of all animals--nearly the entire
animal kingdom--were lost in what is thought to be the worst extinction in
history.

Some 208 million years ago, another mass extinction took a toll primarily
on sea creatures, but also some land animals. And 65 million years ago,
three quarters of all species-including the dinosaurs-were eliminated.

Among the possible causes of these mass extinctions are volcanic
eruptions, meteorites colliding with the earth, and a changing climate.
After each extinction, it took upwards of 10 million years for biological
richness to recover. Yet once a species is gone, it is gone forever.

The consensus among biologists is that we now are moving toward another
mass extinction that could rival the past big five. This potential sixth
great extinction is unique in that it is caused largely by the activities
of a single species. It is the first mass extinction that humans will
witness firsthand-and not just as innocent bystanders.

While scientists are not sure how many species inhabit the planet today,
their estimates top 10 million. Yet each year thousands of species,
ranging from the smallest microorganisms to larger mammals, are lost for
good. Some disappear even before we know of their existence.

The average extinction rate is now some 1,000 to 10,000 times faster than
the rate that prevailed over the past 60 million years. Throughout most of
geological history, new species evolved faster than existing species
disappeared, thus continuously increasing the planet's biological
diversity. Now evolution is falling behind.

Only a small fraction of the world's plant species has been studied in
detail, but as many as half are threatened with extinction. South and
Central America, Central and West Africa, and Southeast Asia--all home to
diverse tropical forests--are losing plants most rapidly.

Today nearly 5,500 animal species are known to be threatened with
extinction. The IUCN-World Conservation Union's 2003 Red List survey of
the world's flora and fauna shows that almost one in every four mammal
species and one in eight bird species are threatened with extinction
within the next several decades. (For access to IUCN's Red List of
Threatened Species database, see www.redlist.org).

Of 1,130 threatened mammal species, 16 percent are critically
endangered--the highest threat level. This means that 184 mammal species
have suffered extreme and rapid reduction in population or habitat and may
not survive this decade. Their remaining numbers range from under a few
hundred to, at most, a few thousand individuals. For birds, 182 of the
1,194 threatened species are critically endangered.

Although the status of most of the world's mammals and birds is fairly
well documented, we know relatively little about the rest of the world's
fauna. Only 5 percent of fish, 6 percent of reptiles, and 7 percent of
amphibians have been evaluated. Of those studied, at least 750 fish
species, 290 reptiles, and 150 amphibians are at risk. Worrisome
signs--like the mysterious disappearance of entire amphibian populations
and fishers' nets that come up empty more frequently--reveal that there
may be more species in trouble. Of invertebrates, including insects,
mollusks, and crustaceans, we know the least. But what is known is far
from reassuring.

At the advent of agriculture some 11,000 years ago, the world was home to
6 million people. Since then our ranks have grown a thousandfold. Yet the
increase in our numbers has come at the expense of many other species.

The greatest threat to the world's living creatures is the degradation and
destruction of habitat, affecting 9 out of 10 threatened species. Humans
have transformed nearly half of the planet's ice-free land areas, with
serious effects on the rest of nature. We have made agricultural fields
out of prairies and forests. We have dammed rivers and drained wetlands.
We have paved over soil to build cities and roads.

Each year the earth's forest cover shrinks by 16 million hectares (40
million acres), with most of the loss occurring in tropical forests, where
levels of biodiversity are high. Ecologically rich wetlands have been cut
in half over the past century. Other freshwater and terrestrial ecosystems
have been degraded by pollution. Deserts have expanded to overtake
previously vegetated areas, accelerated in some cases by overgrazing of
domesticated animals.

A recent study of 173 species of mammals from around the world showed that
their collective geographical ranges have been halved over the past
several decades, signifying a loss of breeding and foraging area. Overall,
between 2 and 10 percent of mammal populations (groups of a single species
in a specific geographical location) are thought to have disappeared along
with their habitat.

Direct human exploitation of organisms, such as through hunting and
harvesting, threatens more than a third of the listed birds and mammals.
Other threats to biodiversity include exotic species, often transported by
humans, which can outcompete and displace native species.

A recent survey of some 1,100 animal and plant species found that climate
change could wipe out between 15 and 37 percent of them by 2050. Yet the
actual losses may be greater because of the complexity of natural systems.
The extinction of key species could have cascading effects throughout the
food web. As John Donne wrote, "no man is an island." The same is true for
the other species we share this planet with: the loss of any single
species from the web of life can affect many others.

Healthy ecosystems support us with many services--most fundamentally by
supplying the air we breathe and filtering the water we drink. They
provide us with food, medicine, and shelter. When ecosystems lose
biological richness, they also lose resilience, becoming more susceptible
to the effects of climate change, invasions of alien species, and other
disturbances.

The 1992 Convention on Biological Diversity provides a framework for
countries to conserve biological diversity and promote sustainable
development. It has been signed by 168 countries, notably excluding the
United States. The parties, which recently held their seventh conference
in February 2004 in Kuala Lumpur, have set a target of substantially
reducing biodiversity loss by 2010. Yet the convention lacks mechanisms
for action and enforcement, which may make it difficult to achieve the
target.

Consciously avoiding habitat destruction and mitigating the effects of
land use change, reducing the direct exploitation of plants and wildlife,
and slowing climate change can help us stop weakening the very
life-support systems we depend on. While this may be the first time in
history that a single species can precipitate a mass extinction event, it
is also the first time in history that a single species can act to prevent
it.


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