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Planetary Boundaries? Go Ask the Romans

Scientists propose guardrails for how far mankind can push the planet tomorrow, while others examine how far collapsed civilizations pushed it yesterday.

At the turn of the century, atmospheric chemist Paul Crutzen introduced a new phrase for the current age: Anthropocene. It was a nod to the "Holocene," the geologic term for the existing time period that began about 12 millennia ago; it substituted the prefix "anthropo-" to reflect humankind's impact on the planet.

Like all scientific terms, Anthropocene is ostensibly a neutral coinage to reflect the scale of change that human activity has had on the geologic landscape. But in reality, it's anything but a compliment.

Now Crutzen, a professor at Germany's Max Planck Institute for Chemistry, has joined an all-star lineup of scientists from various disciplines to point out what they believe are the "planetary boundaries" of abuse that ol' Mother Earth can take.

Robert Constanza, an ecological economist and director of the University of Vermont's Gund Institute for Ecological Economics, was among those all-stars present last summer in Sweden to kick off discussion on the boundaries. "You get a group of scientists and other stakeholders together for a week or two, and they focus on synthesis rather than simply generating more data — which is what scientists tend to do," he explained with a chuckle, "and you put that data together, and you make some real information or knowledge out of it."

Their synthesis was condensed into a four-page paper, "A safe operating space for humanity," which appeared in last week's edition of the influential journal Nature. Accompanying it are seven commentaries from luminaries such as William H. Schlesinger and Cristian Samper.

Hard Number for Hard Truths
It's not comforting reading, and once you get past the "eroded resiliency" and "undesired traits" of science-speak, you realize it wasn't meant to be.

"Now, largely because of a rapidly growing reliance on fossil fuels and industrialized forms of agriculture, human activities have reached a level that could damage the systems that keep Earth in the desirable Holocene state," the paper warns right off the bat. "The result could be irreversible and, in some cases, abrupt environmental change, leading to a state less conducive to human development."

The 29 co-authors, led by Johan Rockstrom of the Stockholm Resilience Center, subdivided the world's human-caused woes into nine areas reflecting planetary processes under assault, ranging from old favorites like climate change and the thinning ozone layer to shortfalls in fresh water and acidifying oceans.

For each process they hammered out an actual measurable boundary — a "safe distance from dangerous thresholds" — for a key process or state that essentially defined the problem. Examples are the percentage of global land cover converted to cropland or the amount of nitrogen removed from the atmosphere for human use. Boundaries for two of the nine — "atmospheric aerosol loading" (i.e. junk in the air) and chemical pollution — have yet to be determined.

"The underlying paradigm was this idea of tipping points or thresholds," Constanza explained. "We know that complex systems have those kinds of dynamics; our goal was to say that each of these nine probably has a tipping point. We don't know exactly where it is, but we're better off not getting too close to it, so that's where the guardrails were set.

"Once we did that, we sort of said we've already gone outside the guardrails; the question is, how long can we stay outside the guardrails without causing real problems?"

The scientists' data crunching determined that mankind has jumped the guardrails in three areas. First Worlders have been reading about two of them, climate change and loss of biodiversity, over breakfast for decades. The third is the nitrogen cycle, which when out of whack, among other things, pollutes water and generates additional greenhouse gases.

On climate change, the authors noted that the scientific community is converging on the "2-degree guardrail" approach, which would contain global warming to no more than 2 centigrade degrees above where the mean temperature was in the pre-industrial days. To achieve that ambitious goal, the authors created one of their hardest boundaries, suggesting that the carbon dioxide in the air not exceed 350 parts per million (it's currently 387, they report) and that the gap between energy radiation reaching the Earth and that leaving through the upper atmosphere (known as "radiative forcing") not exceed one watt per square meter. That figure is currently 1.5 watts, and before the Industrial Revolution it was roughly at equilibrium.

On biodiversity, the authors propose a loss rate of 10 species each year per million species on Earth — a rate at least one-tenth of the current carnage but still an estimated 10 to 100 times the preindustrial rate. Despite this accelerated destruction, finding a boundary here proved elusive.

"From an Earth-system perspective," the paper reads, "setting a boundary for biodiversity is difficult. Although it is now accepted that a rich mix of species underpins the resilience of ecosystems, little is known quantitatively about how much and what kinds of biodiversity can be lost before this resilience is eroded."

Excessive nitrogen, the authors figure, is being removed from the atmosphere at about four times the highest rate it should (121 million tons per year, compared to the 35 million tons boundary and the zero of preindustrial days). Setting a useful value on this nitrogen (and phosphorus) cycle perplexed the authors, and they term their published boundary as a "first guess."

Commentators in Nature generally responded that the planetary boundaries concept was valuable, but did ask pointed questions about numbers assigned or the methods applied in their areas of expertise -- the kinds of criticisms the authors expected and welcome.

Schlesinger, president of the Cary Institute of Ecosystem Studies, was more biting, implying that boiling the nuances down to a single value was akin to teaching to the test. "Unfortunately, policymakers face difficult decisions," he wrote, "and management based on thresholds, although attractive in its simplicity, allows pernicious, slow and diffuse degradation to persist nearly indefinitely. ... Setting boundaries is fine, but waiting to act until we approach these limits merely allows us to continue with our bad habits until it's too late to change them."

Learning From Imperial Rome
That a group of 29 have arbitrarily assigned boundaries to human development might in itself seem like hubris, but Costanza ascribes a more modest — but terribly serious — intent. It might be summed up as, "Get off your duff, world."

"We acknowledge that [this is] more of a call to arms, a way of looking at it, rather than the last word," he explained. "There's a lot of work that needs to be done. Look at the amount of work that's been done on the climate questions over the last couple decades. Well, if we did the same amount of work on each of the other nine, we'd probably be in a better position to say whether those guardrails should be placed."

This Stockholm group isn't the first team of researchers to try and establish global integrated models; the urge goes at least as far back as the Club of Rome's The Limits to Growth in the early 1970s.

"The problem is," Costanza asked, "how do we know those models are telling us anything other than making projections into the future? So the only way to test and really calibrate those integrated models, we think, is to go back historically and look at civilizations' interactions that have occurred over a long-enough time period so that we see whether our models capture those complex interactions."

Another collaborative project — and which shares Crutzen, Costanza and paper co-authors ecologist Carl Folke, archaeologist Sander van der Leeuw and oceanographic biologist Katherine Richardson — is the "Integrated History and future Of People on Earth," or IHOPE. (The secretariat for IHOPE is hosted by the Stockholm Resilience Centre, which is directed by Rockstrom and has paper co-author Carl Folke as its science director.)

IHOPE reverse-engineers history, comparing what computer models suggest must have happened with what actually happened.

"It's an attempt to put together an emerging environmental and climate history, put together with human history, to try to build some integrated models that can help us to ... look into the future," said Costanza, speaking during a morning coffee break with an IHOPE working group at the National Center for Ecological Analysis and Synthesis in Santa Barbara, Calif. "... We can use those same kind of models to help us build a more sustainable and desirable future."

Their three main case studies have been the Roman Empire, the Mayan empire and the American Southwest. "We're only now sort of capable of applying some of these ideas from complex systems bearing to these historical problems in the past," he continued, and then took aim at single-variable explanations like, say, lead in their cookware. "It's been largely descriptive or fairly simple causal models that have been used. I think we take a whole different approach: that modern science and computing and simulation tools [bring new information] to bear on these types of problems."

While ecological reasons have been posited for the Maya and the Anasazi collapses, those raised on a steady diet of Gibbons and Grant may balk at this approach being applied to the Romans and their Western-styled imperium. But as Gen. Omar Bradley once said, "Amateurs study strategy, professionals study logistics," and what is ecology but logistics at its most basic?

Costanza adds: "By building a dynamic computer model that we apply to, for example, the Roman Empire, and then if we can test that against what really happened and say, 'Well, this model reproduces what we know happened there,' then we can start playing all sorts of interesting games with it. We can start saying, 'What if the Romans, instead of trying to expand the reach of the empire at a certain point, what if they had decided to consolidate and stay where they were. Would that have led to a very different result?

"What if the climate, something called the 'Roman climate optimum,' ... throughout the Roman Empire was particularly stable and was particularly amenable to growing grains in southern Germany that didn't occur either before or after the empire? So, what influence did that have on the growth and decline of the empire, and what if the climate had been different? What if that period had extended? Would the empire have gone on longer or would it have collapsed anyway?"

If talk like that prompts memories of Jared Diamond's 2005 best-seller Collapse, Costanza for one won't deny it. "We're sort of taking the Jared Diamond idea forward. We're kind of applying science to the task of helping us to learn from the past to help us build a better future."

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