Scientists say human beings pushing 'planetary boundaries'
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Scientists say human beings pushing 'planetary boundaries'
September 23, 2009
A report to be published Thursday in the journal Nature says the
nitrogen cycle has been �significantly� perturbed by massive amounts of
nitrogen-based fertilizer used in farming, which is now polluting
waterways and costal zones.
A report to be published Thursday in the journal Nature says the
nitrogen cycle has been �significantly� perturbed by massive amounts of
nitrogen-based fertilizer used in farming, which is now polluting
waterways and costal zones.
Photograph by: Brian J. Gavriloff , Edmonton Journal
Three key "planetary boundaries" have been crossed, according to an
international research team that says human beings have collectively
gone too far in pushing other species to extinction and perturbing
global climate and nitrogen cycles.
The scientists argue human activities must stay within defined
boundaries for nine Earthly systems to avoid catastrophic environmental
change.
They are proposing a framework of "planetary boundaries" to measure
stress to the Earth, and define "a safe operating space" for human
existence on the planet.
For three of the nine boundaries � the rate at which species are being
lost, human induced climate change linked to use of fossil fuels, and
the global nitrogen cycle that is being disrupted by farming � the
acceptable limit has already been passed, they say in a report to be
published Thursday in the journal Nature.
"Today the rate of extinction of species is estimated to be 100 to
1,000 times more than what could be considered natural," they report.
"As with climate change, human activities are the main cause of the
acceleration."
They say the nitrogen cycle has been "significantly" perturbed by
massive amounts of nitrogen-based fertilizer used in farming and which
is now polluting waterways and costal zones.
If that weren't bad enough, they say humanity appears to be fast
approaching the boundaries for freshwater use, for converting forests
and other natural ecosystems to cropland, for acidification of the
oceans and for the phosphorous cycle.
Boundaries also exist for atmospheric aerosol loading and chemical
pollution, but there is not enough data to define these yet, says the
group, led by Johan Rockstrom, at Stockholm University in Sweden.
It includes several noted environmental scientists, including outspoken
U.S. climatologist James Hansen at NASA and Paul Crutzen at Germany's
Max Planck Institute, who won a Nobel Prize for his work on ozone
depletion. Crutzen has argued that attempts to limit man-made
greenhouse gases are so pitiful that a radical contingency plan is
needed.
Overstepping these planetary boundaries could lead to abrupt
environmental changes "with deleterious or potentially even disastrous
consequences for human society," they say.
Even if only one boundary is passed, it can impact other systems. They
note climate change is expected to greatly accelerate species loss: "Up
to 30 per cent of all mammal, bird and amphibian species will be
threatened with extinction this century."
The scientists say the planet's environment has been unusually stable
over the past 10,000 years, which has seen human civilizations "arise,
develop and thrive." Since the industrial revolution, they say human
actions have become the "main driver of global environmental change."
Unchecked the activities could push the Earth system outside the stable
environmental state "with consequences that are detrimental or even
catastrophic for large parts of the world."
The idea of planetary boundaries builds on the "Limits of Growth,"
commissioned by the Club of Rome global think-tank in 1972, and the
more recent concept of ecological footprints, which says it would take
three to four extra planets if all human beings lived and consumed like
North Americans.
Rockstrom and his colleagues are even more ambitious in trying to
define Earth's capacity to support us and define the thresholds
humanity can, or should, not cross.
The planetary boundaries proposal is getting mixed reviews, with some
praising it and others trashing the idea.
Myles Allen, a climate physicist at Oxford University, says the
proposed boundary for the climate system presents an "unnecessary
distraction" from the "immediate challenge" of reducing greenhouse gas
emissions.
William Schlesinger, president of Cary Institute of Ecosystem Studies
in New York, writes in a commentary also published in Nature: "Ongoing
changes in global chemistry should alarm us about threat to the
persistence of life on Earth, whether or not we cross a catastrophic
threshold anytime soon."