PLANETARY BOUNDARIES: Scientists have proposed a list of planetary thresholds that might wreak havoc if crossed.
Image: Courtesy of NASA
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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."
Earth System Threshold Measure Boundary Current Level Preindustrial
Climate Change CO2 Concentration 350 ppm 387 ppm 280 ppm
Biodiversity Loss Extinction Rate 10 pm >100 pm* 0.1-one pm
Nitrogen Cycle N2 Tonnage 35 mmt** 121 mmt 0
Phosphorous Cycle Level in Ocean 11 mmt 8.5-9.5 mmt –1 mmt
Ozone Layer O3 Concentration 276 DU# 283 DU 290 DU
Ocean Acidification Aragonite^^ Levels 2.75 2.90 3.44
Freshwater Usage Consumption 4,000 km3^ 2,600 km3 415 km3
Land Use Change Cropland Conversion 15 km3 11.7 km3 Low
Aerosols Soot Concentration TBD TBD TBD
Chemical Pollution TBD TBD TBD TBD
*pm=per million
**mmt=millions of metric tons
#DU=dobson unit
^km3=cubic kilometers
^^Aragonite is a form of calcium carbonate. Measurement is in global mean saturation state.
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."
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15 Comments
Add CommentThis sounds kind of familiar. Oh yes, I recall. We heard similar things on earth day in 1970.
Reply | Report Abuse | Link to this“Demographers agree almost unanimously on the following grim timetable: by 1975 widespread famines will begin in India; these will spread by 1990 to include all of India, Pakistan, China and the Near East, Africa. By the year 2000, or conceivably sooner, South and Central America will exist under famine conditions….By the year 2000, thirty years from now, the entire world, with the exception of Western Europe, North America, and Australia, will be in famine.”
• Peter Gunter, professor, North Texas State University
“We have about five more years at the outside to do something.”
• Kenneth Watt, ecologist
“Civilization will end within 15 or 30 years unless immediate action is taken against problems facing mankind.”
• George Wald, Harvard Biologist
“By…[1975] some experts feel that food shortages will have escalated the present level of world hunger and starvation into famines of unbelievable proportions. Other experts, more optimistic, think the ultimate food-population collision will not occur until the decade of the 1980s.”
• Paul Ehrlich, Stanford University biologist
But, I'm sure, this time they are correct.
it is curious that the most importat factor in the whole system analysis has not been taken in consideration. The overpopulation of the globe. We are too many. If (as I suppose) the aim is, at least keeping the actual techonology and spread it all over the human society (I know..it is, by itself, a utopia) we are far too many. A well balanced relation between environment (biotic and abiotic) and a confortable human population should not grow beyond the 1 billion. So.. what we do with the surplus ? Who. is going to put the "reverse" in this mad train ?
Reply | Report Abuse | Link to thisAs an ecologist.. i am so sorry.
by the way.. i like the term..
Reply | Report Abuse | Link to this.. in due prospective (pronunciation wise..)
Ant.thropo.cene ?
The era of the Ant's spreading ??
.. woww.. no better term, indeed .. ;)
I'd take issue with the notion that our unchecked growth has led to unprecedented prosperity. I've seen numbers that suggest we have significantly less disposable income than our grandparents did, even though we work more. Meanwhile, the cost of food is falling, but the cost of good food is not – indeed, it may be as expensive as ever. I'd say we've created a pretty fair simulacrum of prosperity, but that's not the same as the real deal.
Reply | Report Abuse | Link to this"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"
Reply | Report Abuse | Link to thisThis sort of thing really bothers me. How idiotic can people be? They mention a "stable state" which happened to come after AN ICE AGE. Does that sound like stability?? There has never been true stability on our planet, just periods of slow or fast change. Yes humans have contributed to the current change and of course I think we should work to reduce our impact, but we cannot top the world from changing and we must recognize that.
The mentality that the world can be stable is illogical and derives from limited human perception and our short life-span. Of course books and science are supposed to solve this problem...
"They mention a "stable state" which happened to come after AN ICE AGE. Does that sound like stability??"
Reply | Report Abuse | Link to thisYep. The weight of evidence currently suggests that the actual interglacial epoch (the Holocene) has a fairly stable climate.
http://en.wikipedia.org/wiki/File:Holocene_Temperature_Variations.png
"But, I'm sure, this time they are correct."
Reply | Report Abuse | Link to thisHum, they were generally correct. This would be obvious to you if you take the time to read the papers, reports and books which appeared after the publishing of The Limits to Growth, The Population Bomb and other similar books. Unfortunately, this consumes more time and requires some numeracy and science background than simple quote-mining and headless ranting. You can start here:
- http://www.mnforsustain.org/meadows_limits_to_growth_30_year_update_2004.htm
- http://www.csiro.au/files/files/plje.pdf
- http://www.greatchange.org/ov-simmons,club_of_rome_revisted.pdf
- http://www.manicore.com/anglais/documentation_a/club_rome_a.html
I thought it was kind of scary to find out the difference in carbon dioxide from today at 387 ppm compared to the 280 ppm in predindustrial times. It makes complete sense now why our environment is having so many problems not only with carbon dioxide but with nitrogen and eventually it looks like all those 9 factors will be having problems if we continue at this rate. The human way of life is just deminishing our earth and if we want to remain on it there is an obvious need for change
Reply | Report Abuse | Link to thisOne of my biggest worries about climate change stems from the chaotic nature of it. This is because weather and climate are determined by turbulence, a quasi-fractal phenomenon at all scales. Turbulence is the factor that can gear up small changes to a much larger scale, causing possible tipping-points which could have catastrophic effects locally or world-wide. I just hope models will be able to detect such outcomes soon enough, as scientific data continues to accumulate to improve modelling.
Reply | Report Abuse | Link to this"But, I'm sure, this time they are correct."
Reply | Report Abuse | Link to thisJust because a number of technological, medical and agricultural innovations enabled us to exceed the then-apparent limits to the planet's carrying capacity for humanity, it does not follow that these forecasts (even from the much maligned Malthus) were wrong in principle - there are upper limits for any organism, if only because there is a limit to the amount of energy arriving on the Earth from the Sun, very little of which is actually captured and converted into such necessities as food.
If we can improve on plants then we may push this a little further, but we still need oxygen, water, habitable temperatures and healthy recycling of a variety of materials.. these require a large number of other organisms to be able to live healthily too.
We really do need to curb our hubris, and our self-indulgences, including the near-universal belief that unrestrained reproduction is a fundamental right (even duty) - but these are inconvenient truths...
Thanks, I am glad that fresh water consumption boundary is higher than the present level.
Reply | Report Abuse | Link to thisIt has become obvious that science often struggles with complex concepts. As the result simplistic solutions are ignored!!
Reply | Report Abuse | Link to thisFirst: Reflectivity!!! The more white present {Reflective color} the less the surface will heat up in sunlight. This concept can be demonstrated by parking a white car next to a black car in 90Degree heat. Now put your left hand on one and right hand on the other. The black car will burn you of course. It makes sense to me that during an "ice age" there is more white on the surface thus {more reflectivity}less heat.
Now if you look at what most roofs are made of {asfalt}they heat daily under sunlight. These roofs remain hot well into the night. Now what if: All structures around the planet had reflective or white roofs. This would be much more intelligent than trying to medicate the environment with particulate matter.
Now I am no scientist but it only makes sense to me that if Nitrogen and CO2 levels are to high in the annual cycle that cooling the surface "overall" will trigger the surface absorption mechanism which most likely occured during the ice age. The hotter the atmosphere the more aloft the problem. I have other solutions but they involve crashing a gravel truck into a coal train.
Sincerely J.R.
It has become obvious that science often struggles with complex concepts. As the result simplistic solutions are ignored!!
Reply | Report Abuse | Link to thisFirst: Reflectivity!!! The more white present {Reflective color} the less the surface will heat up in sunlight. This concept can be demonstrated by parking a white car next to a black car in 90Degree heat. Now put your left hand on one and right hand on the other. The black car will burn you of course. It makes sense to me that during an "ice age" there is more white on the surface thus {more reflectivity}less heat.
Now if you look at what most roofs are made of {asfalt}they heat daily under sunlight. These roofs remain hot well into the night. What if: All structures around the planet had reflective or white roofs. This would be much more intelligent than trying to medicate the environment with particulate matter.
Now I am no scientist but it only makes sense to me that if Nitrogen and CO2 levels are to high in the annual cycle that cooling the surface "overall" will trigger the surface absorption mechanism which most likely occured during the ice age. The hotter the atmosphere the more aloft the problem. I have other solutions but they involve crashing a gravel truck into a coal train far intelligent but very symbolic.
Sincerely J.R.
Just came across this -- @"Soccerdad" your challenge could be a valuable contribution -- but if you're going to quote people please provide exact citations. There is too much sloppy innuendo in today's public discourse -- rigor in assertion is necessary -- irrespective of the polemical intent of your discourse... Thanks!
Reply | Report Abuse | Link to thisThanks. Spot on!
Reply | Report Abuse | Link to this