STUDY FINDS EARTH'S ECOSYSTEMS ON VERGE OF SUDDEN COLLAPSE
The following is a summary of news reports about the study published
on
October 11, 2001 in the journal NATURE, followed by the complete text
of
the NATURE article ["Catastrophic Shifts In Ecosystems," Marten
Scheffer, Steve Carpenter, Jonathan A. Foley, Carl Folke, and Brian
Walker, NATURE #413, 10/11/01, pp. 591-596]. Links to sources
provided
at end.
A shocking and groundbreaking new scientific study by an
international
consortium of scientists has concluded that humanity's assault on the
environment has left many ecosystems - from coral reefs and tropical
forests to lakes and coastal waters - in such a fragile state that
the
slightest disturbance, from a dry spell to a fire or flood, may push
them into a catastrophic collapse.
The study, published in the prestigious journal NATURE, found that
human
impacts on many of the world's ecosystems could cause them to
abruptly
shift with little or no warning from their apparently stable natural
condition to very different, diminished conditions far less able to
support diversity of life, including human.
"Models have predicted this, but only in recent years has enough
evidence accumulated to tell us that resilience of many important
ecosystems has become undermined to the point that even the slightest
disturbance can make them collapse," said Marten Scheffer, an
ecologist
at the University of Wageningen in the Netherlands and lead author of
the study.
Conventional scientific and conservation thinking has been that
ecosystems such as lakes, oceans, coral reefs, woodlands or deserts
respond slowly and steadily to climate change, nutrient pollution,
habitat degradation and other human environmental impacts. But the
new
study shatters this paradigm, finding instead that, after decades of
continuous change imposed by human activity, many of the world's
natural
ecosystems are now susceptible to sudden catastrophic change. In
dramatic contrast to conventional environmental thinking, the
investigators paint a picture of unexpectedly sudden, drastic
switches
of state, from lush, lake- dotted forests teeming with plants and
animals to scorching, parched deserts devoid of all but the hardiest
of
lifeforms, for example.
"In approaching questions about deforestation or endangered species
or
global climate change, we work on the premise that an ounce of
pollution
equals an ounce of damage," said co-author Jonathan Foley, a
University
of Wisconsin-Madison climatologist and director of the Center for
Sustainability and the Global Environment at the Institute for
Environmental Studies at UW-Madison. "It turns out that assumption is
entirely incorrect. Ecosystems may go on for years exposed to
pollution
or climate changes without showing any change at all and then
suddenly
they may flip into an entirely different condition, with little
warning
or none at all."
"The idea that nature can suddenly flip from one kind of condition to
another is sobering," said Foley, who said that such changes can be
irreversible. "For hundreds of years, we've been taught to think in
very
linear ways; we like to think of nature as being simple. But now we
know
that we can't count on ecosystems to act in nice simple ways."
This new awareness of the nonlinearity of ecological change - that
stressed ecosystems, given the right nudge, are capable of slipping
rapidly from a seemingly steady state to something entirely different
-is building in the scientific community, said coauthor Stephen
Carpenter, a limnologist at the University of Wisconsin- Madison and
immediate past president of the Ecological Society of America. An
understanding that ecosystems engage in a delicate balancing act has
emerged as scientists have become more skillful at assessing entire
ecological systems.
"We realize that there is a common pattern we're seeing in ecosystems
around the world," said Carpenter, an authority on lakes. "Gradual
changes in vulnerability accumulate and eventually you get a shock to
the system, a flood or a drought, and boom, you're over into another
regime. It becomes a self-sustaining collapse."
"We systematically alter conditions on the earth, such as temperature
and nutrient levels. We usually assume that things are okay if nature
is
not changing too strongly and assume that we may always reverse
change
by taking 'a step back' if things seem to become too bad," said
Scheffer. "Our article shows that this does not hold. We may see
little
effect until the breakpoint. Once the catastrophic change has
occurred,
the way back is typically very difficult."
The study found that these cataclysmic alterations result from the
breakdown of resilience of ecosystems being relentlessly degraded by
human activities. The implications of losing ecosystem resilience,
the
paper's authors say, are "profound" in light of current resource
management. "Regime shifts," they write, "can imply a drastic loss of
biodiversity as well as utility for humans."
"We are now witnessing a human-induced, tremendously rapid change in
conditions, compared to what happened in most of the ancient past,"
Scheffer said. "None of the changes ahead will stop nature from
functioning in one way or another. However, some of the rapid
switches
may take us by surprise and cause not only a tremendous loss of
biodiversity but also play havoc with human use of nature in an
economic
sense as well as in a wider sense."
"All of this is set up by the growing susceptibility of ecosystems,"
Carpenter said. "A shock that formerly would not have knocked a
system
into another state now has the potential to do so. In fact, it's
pretty
easy." Carpenter cited Lake Mendota, an urban lake in Madison,
Wisconsin, that is perhaps the most studied lake in the world. It has
seen a steady influx of nutrients such as phosphorus from chemical
runoff from farms and suburban lawns as the land around it has been
developed and artificially enriched.
"Over the past 150 years, we've put a huge amount of phosphorus into
the
mud of Lake Mendota, and it's prompted a lot of algae growth in a
lake
that was once very clear," Carpenter said. In 1993, scientists
watched
nutrient levels rise sharply after a single heavy rain washed
nutrients
into the lake. "This phosphorus buildup has made it easy for Lake
Mendota to go into a eutrophic state," characterized by green surface
scums, Carpenter said. Reversing eutrophication is difficult because
of
the phosphorus buildup in soils and sediments.
Evidence supporting the author's assertions spans the globe, other
scientists said.
"I find that my own work in southern New Mexico, where we have seen a
widespread change from semiarid grassland systems that were
productive
rangelands to arid shrublands, substantiates what these authors
describe
in the desert regions," said William Schlesinger, James B. Duke
professor of biogeochemistry and dean of the Nicholas School of the
Environment and Earth Sciences at Duke University in Durham, N.C.
"Abrupt environmental change has affected these ecosystems
worldwide."
"We should not be complacent about the response of ecosystems to
ongoing
global changes in environment," Schlesinger said. "What may seem
gradual
and unimportant could produce big, undesirable changes in ecosystems
and
the productivity of food and forestry systems upon which we all
depend."
SOURCES:
http://www.sciencedaily.com/releases/2001/10/011011065827.htm
http://www.enn.com/news/enn-stories/2001/10/10122001/s_45241.asp
http://www.eurekalert.org/pub_releases/2001-10/uow-acc100501.php
http://www.nature.com/nature/links/011011/011011-3.html (subscription
required for access
www.sciencedaily.com/releases/2001/10/01...
