Alister Doyle, Reuters 23 Sep 09:
OSLO (Reuters) - A new users' guide is needed to help protect the Earth from dangerous changes such as global warming and extinctions of animals and plants caused by humans, scientists said.
A group of 28 experts suggested nine key areas, such as freshwater use, chemical pollutants or changes in land use, where governments could define limits to ensure a "safe operating space for humanity."
"Today we are clearly driving development in the world blindfolded," Johan Rockstrom, leader of the study and director of the Stockholm Resilience Center at Stockholm University, told Reuters of a lack of international guidelines.
"We are not considering the risks that there are deep holes we can drive into," he told Reuters. The call, for setting "planetary boundaries," was published in Thursday's edition of the journal Nature.
Rockstrom said there were signs human activities had already pushed the world into the danger zone because of global warming, a high rate of extinctions of animals and plants and pollution caused by nitrogen, mainly used in fertilizers.
Among limits, they suggested capping the percentage of global land area converted to cropland at 15 percent. At the moment, the percentage is 11.7 percent, they said.
They added that concentrations of carbon dioxide, the main greenhouse gas, should be limited to 350 parts per million of the atmosphere -- below current levels of 387 ppm. Human freshwater use should be capped at 4,000 square km (1,545 sq mile) a year -- against 2,600 sq km now.
CREDITABLE ATTEMPT
Nature said in an editorial the proposed indicators were a "creditable attempt" to quantify limits on human use of the planet. However, it noted, for instance, that fertilizers caused pollution yet helped feed millions of people.
Hans Joachim Schellnhuber, head of the Potsdam Institute for Climate Impact Research and a co-author of the study, said there were growing risks of abrupt and possibly irreversible changes.
"Observations of an incipient climate transition include the rapid retreat of summer sea ice in the Arctic Ocean, melting of almost all mountain glaciers around the world, and an increased rate of sea-level rise in the past 10-15 years," he said.
The scientists said the current relatively stable temperatures of the Holocene era since the end of the last Ice Age 10,000 years ago was under threat from human -- or anthropogenic -- activities.
"Since the Industrial Revolution, a new era has arisen, the Anthropocene, in which human actions have become the main driver of global environmental change," they wrote.
Grappling with the Anthropocene: Scientists Identify Safe Limits for Human Impacts on Planet
Scientists propose a list of planetary boundaries for human impacts ranging from biodiversity loss to the global nitrogen cycle
David Biello, Scientific American 23 Sep 09;
The scale of mankind's impact on the globe is becoming more and more apparent: We have achieved a species extinction rate to rival great extinction events of all geologic time as well as a rapidly acidifying ocean, dwindling ice caps, and even sinking river deltas, a new study from scientists at the University of Colorado at Boulder reveals. No wonder then that some geologists and other scientists have dubbed the modern epoch the Anthropocene. And now an international group of 28 scientists has taken a preliminary stab at setting some concrete environmental thresholds for the planet.
Johan Rockström of Stockholm University and his colleagues are proposing nine "planetary boundaries" in this week's Nature. (Scientific American is part of the Nature Publishing Group.) Ranging from climate change to chemical pollution, the boundaries are meant to set thresholds, or safe limits, for natural systems with respect to human impact.
"We have reached the planetary stage of sustainability, where we are fiddling with hard-wired processes at the global Earth-system scale," Rockström says. "What are the Earth-system processes that determine the ability of the [planet] to remain in a stable state?"
The research takes as its desired stable state the Holocene epoch, the 10,000 years since the last ice age during which human civilization has flourished, and attempts to identify the key variables that might push planetary cycles past safe thresholds.
So, for example, the key variable for climate change is atmospheric carbon dioxide concentration as well as its attendant rise in the amount of trapped heat. At present, atmospheric CO2 has reached more than 387 parts per million (ppm), well above the preindustrial figure of 280 ppm. So, the estimated safe threshold identified by the scientists, including NASA climatologist James Hansen, is 350 ppm, or a total increased warming of one watt per meter squared (current warming is roughly 1.5 watts per meter squared).
"We begin to quantify, very roughly, where we think these thresholds might be. All have huge error bars," says ecologist Jonathan Foley director of the University of Minnesota's Institute on the Environment, one of the authors. "We don't know exactly how many parts per million it would take to stop climate change, but we think it starts at about 350 ppm."
Along with the climate change boundary, humanity has already pushed past the safe threshold in two more of the nine identified boundaries—biodiversity loss and available nitrogen (thanks to modern fertilizers). And, unfortunately, many of the processes impact each other, as well. "Crossing one threshold makes the others more vulnerable," Foley adds. For example, "biodiversity [loss] on a really hot planet is accelerated."
In associated commentaries published online this week in Nature Reports Climate Change, several scientists criticize the precise thresholds set, although they laud the effort. Biogeochemist William Schlesinger of the Cary Institute of Ecosystem Studies argues that the limits on phosphorus fertilizer are too lenient and can allow "pernicious, slow and diffuse degradation to persist nearly indefinitely." Allowing human water use, largely for agriculture, to expand from 2,600 cubic kilometers today to 4,000 cubic kilometers in the future will allow further degradation at such environmental disaster sites as the drying Aral Sea in Asia and seven major rivers, including the Colorado in the U.S., that no longer reach the sea, notes David Molden, deputy director general for research at the International Water Management Institute in Sri Lanka.
Even the 350-ppm limit for carbon dioxide is "questionable," says physicist Myles Allen of the Climate Dynamics Group at the University of Oxford, and focusing instead on keeping cumulative emissions below one trillion metric tons might make more sense, which would mean humanity has already used up more than half of its overall emissions budget.
And such efforts to set thresholds have a mixed track record. For instance, the "limits to growth" argument put forward by the Club of Rome in 1972 failed to materialize, thanks in part to some of the innovations listed here, such as increased nitrogen use in industrial agriculture. "A big part of this is feeding 6.7 billion people," Foley says. "We are heading towards nine billion who are going to want to eat more like people in the developed world, and there's the specter of biofuels. Those boundaries look really fragile."
Most importantly, however, regardless of impacts on the planet, the human condition has likely never been better in terms of material prosperity. The question is: "How do you continue to improve the human condition?" Foley asks. "How can we sustain a world that will reach nine billion people without destroying the planet? At least knowing a bit where the danger zones are is a really important first step."
There are grounds for hope. Humanity has crossed one of these thresholds before—diminishing levels of stratospheric ozone due to emissions of ozone-destroying chemicals (the "ozone hole")—and pulled back through international cooperation and the 1989 Montreal Protocol. "We did manage to move ourselves away from the ozone boundary and have made serious efforts at regional levels to protect biodiversity; reduce agricultural pollution, aerosols and water demand; and slow land conversion," says environmental scientist Diana Liverman of the University of Arizona's Institute for the Environment and Society, one of the new thresholds authors. "This provides some hope that we can manage our planetary impact if we choose."
Human damage 'needs limits'
ARC Centre of Excellence for Coral Reef Studies
Science Alert 24 Sep 09;
Humanity needs to act now to avoid threats to human well-being caused by irreversible damage to the Earth, its climate, species and life-supporting systems.
Scientists say it has become essential to define what levels of such human-caused change are ‘safe’ and which are ‘unsafe’, and to stay within these boundaries.
The call comes from 28 of the world’s most eminent environmental scientists, published September 23 in the world’s leading science journal, Nature.
The researchers propose an upper limit of 350 parts per million of CO2 in the atmosphere – a level already exceeded since 1987 - requiring a fast-track reduction in fossil fuels.
“Transgressing the safe boundary of 350ppm will increase the risk of irreversible climate change, such as the loss of major ice sheets, accelerated sea level rise and abrupt shifts in coral reef, forest and agricultural systems,” they caution.
“The increasing level of CO2 in the atmosphere and ocean has caused major damage to coral reefs worldwide over the past 25 years. Allowing it to increase to 450 or higher would be irresponsible and hugely detrimental to millions of people who depend on reefs for food and their livelihood” says Australian co-author Professor Terry Hughes of the ARC Centre of Excellence for Coral Reef Studies and James Cook University.
The researchers also propose that safe boundaries be set to other major human impacts, such as species loss, the effect of fertilisers, ozone depletion, ocean acidification, freshwater use and chemical pollution.
The scientists, who come from many of the world’s leading research institutions, say human activity is now the main driver of global change and is taking the planet down a path where it may be unable to support humanity’s future development.
Human activities – largely resulting from our rapidly growing reliance on fossil fuels and industrialised forms of agriculture – have now reached a magnitude that may trigger irreversible and in some cases abrupt environmental change by damaging the regulatory capacity of the planet, they say.
In the cases of atmospheric CO2, nitrogen fertiliser use and species loss, the Earth has already exceeded the safety zone beyond which irretrievable changes may occur, the paper says.
And we are rapidly approaching the safe upper limits for freshwater use, land clearing and ocean acidification.
“The idea of identifying safe boundaries is based on the tipping-ponts, or thresholds, we see in nature,” explains Professor Hughes. “These are natural limits which, if you exceed them, trigger a sudden large change – a grassland to a desert, or a coral reef to a degraded weed-infested system.”
“Once you’ve crossed the line it is very hard, if not impossible, to get back again. The system you knew is gone for good.”
The impact of human actions now means that the stable climate and conditions of the last ten thousand years, in which civilization had arisen and flourished, are being replaced by a far more unstable Earth, potentially catastrophic for large parts of humanity, the team warns.
“We felt it was urgent to identify future tipping-points, so we can all start thinking about how to avoid passing the point of no-return,” he says.
“Our objective is to define a safe operating space for humanity, to ensure future human wellbeing.”
“We cannot continue to ignore the reality of what is happening to our planet, or to keep hoping it isn’t happening. The evidence is unambiguous that Earth is changing in profound and serious ways – and that we must take action to change some of the things we do. The time to do this is now.”
The scientists argue that humanity faces a choice – between preserving the kind of climate and conditions that cradled the human race as we know it, and an unstable and dangerous future with dire consequences for millions.
“We are beginning to see evidence that some of the Earth’s subsystems are already moving outside their stable Holocene state. These include the rapid retreat of the summer sea ice in the Arctic ocean, the retreat of mountain glaciers around the world, the loss of mass from the Greenland and West Antarctic ice sheets and accelerating rates of sea level rise during the past 10-to-15 years.”
On extinctions, they say: “The rate of extinction of species today is around 100-to-1000 times more than what could be considered natural.”
They also warn that humanity is pulling 35 million tonnes of nitrogen out of the atmosphere for fertiliser production, which is causing havoc in the environment, especially rivers, lakes and coastal seas.
As a starting point they propose ten boundaries which should not be exceeded to avoid crossing dangerous tipping points. These include atmospheric CO2 levels, the rate of species extinction, the over-use of nitrogen and phosphorus in fertilisers, use of fresh water, the clearing of land, ozone depletion, aerosol pollution of the atmosphere and chemical contamination. The detailed rationale for each boundary is explained in a more technical paper at http://www.stockholmresilience.org/planetary-boundaries.
The researchers argue that all of the boundaries are interconnected and it is no use observing one but not the others. “If one boundary is transgressed, then safe levels for other boundaries are also under serious risk. For instance, significant land use changes in the Amazon could influence water resources as far away as Tibet,” they say.
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