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Tipping Points: Can Humanity Break The Planet?

Dire warnings that our localized environmental impacts could trigger global-scale "tipping points" and permanently break the planet have no scientific basis, authors of a new paper argue. Not everyone agrees.
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FILE - This December 1968 file photo provided by NASA shows Earth as seen from the Apollo 8 spacecraft. The images provided by the NASA mission were the first to how the planet in its entirety. NASA, the agency that epitomized the "Right Stuff," looks lost in space and doesn't have a clear sense of where it is going, an independent panel of science and engineering experts said in a stinging report Wednesday. (AP Photo/NASA, File)
FILE - This December 1968 file photo provided by NASA shows Earth as seen from the Apollo 8 spacecraft. The images provided by the NASA mission were the first to how the planet in its entirety. NASA, the agency that epitomized the "Right Stuff," looks lost in space and doesn't have a clear sense of where it is going, an independent panel of science and engineering experts said in a stinging report Wednesday. (AP Photo/NASA, File)

If you're the sort of person who woke up Friday morning worrying not just about the potential for sudden economic chaos following the sequester, but also the potential for human population growth and industrial activity to spur sudden ecosystem collapse on a planetary scale, take heart (and perhaps a Xanax). Some reassuring words are percolating on both fronts -- though as it concerns the planet's health in particular, the accuracy of those reassurances is in question.

On the first point: the sequester's impacts on the wider economy, while almost certainly painful in the long-run, will likely be uneven and gradual. This being an environmental column, I'll leave a fuller dispensation of these ideas to my far more qualified colleagues in the Business section, and you'll also find meditations on the topic here, and here and here.

As for Planet Earth, a paper published Thursday in the journal Trends in Ecology and Evolution suggests that while human society does a very thorough job of modifying and, often enough, permanently and abruptly changing the dynamics of local and regional ecosystems, the collective impact of all this on a planetary scale is too often overstated.

Dire warnings that our localized impacts could trigger global-scale "tipping points," after which the spinning cogs and gears that underpin our entire terrestrial biosphere are thrown abruptly and permanently out of whack, have no scientific basis, the authors argue. Global-scale changes, such that they are, come about smoothly and slowly, they say.

"This is good news because it says that we might avoid the doom-and-gloom scenario of abrupt, irreversible change," Professor Barry Brook, lead author of the paper and director of Climate Science at the University of Adelaide in Australia, said in a statement accompanying the study's release. "A focus on planetary tipping points may both distract from the vast ecological transformations that have already occurred, and lead to unjustified fatalism about the catastrophic effects of tipping points."

"An emphasis on a point of no return is not particularly helpful for bringing about the conservation action we need," Brook added. "We must continue to seek to reduce our impacts on the global ecology without undue attention on trying to avoid arbitrary thresholds."

This, of course, flies directly in the face of a growing body of research over the last several years -- much of it suggesting that there are very real planetary boundaries beyond which the entire terra machina starts to break down. This was the core of an extensive exploration published in the journal Nature in 2009.

In an email message, James E. Hansen, who heads the NASA Goddard Institute for Space Studies and is an adjunct professor at Columbia University's Earth Institute, said that tipping points may unfold more smoothly than people generally understand, but that they represent points of no return nonetheless. He also suggested that dismissing the notion of global tipping points out of hand was a mistake. "Tipping points are real, albeit misunderstood by some people," he said.

Last June, in another paper published in Nature, a team of "biologists, ecologists, complex-systems theoreticians, geologists and paleontologists, from the United States, Canada, South America and Europe," according the University of California, Berkeley, which spearheaded the study, argued that "population growth, widespread destruction of natural ecosystems, and climate change may be driving Earth toward an irreversible change in the biosphere, a planet-wide tipping point that would have destructive consequences absent adequate preparation and mitigation."

The authors of Thursday's study suggest this is nonsense. To prove their point, the team of Australian, American and British scientists looked at the impacts of four fundamental ecosystem influencers: Climate change; land-use changes (turning forest to agricultural land, for example, or native grasslands to pasture); the fragmentation of various habitats; and overall reductions in the richness and diversity of species.

There is little doubt that humans have a hand in all of these, and there is also little doubt they contribute to fundamental and quite often permanent changes in the way local and regional ecosystems work. As a very simple example, think of the fast-growing and aggressive plant kudzu -- artificially introduced to the U.S. by way of Japan in the late 19th century and now, well, everywhere.

Amid a fertile stand of trees and scrub and their dependent wildlife, kudzu can easily take over, strangling the local native vegetation, stripping resident critters of their accustomed food sources, and, at some juncture, causing the interdependent system that had grown up in that spot to collapse, with little practical ability to bounce back. Sure, a new system is in place, but the "regime" has been changed.

The authors of Thursday's study, however, suggest that the local impacts of any stressor -- be it kudzu, or even rising temperatures due to human-driven global warming -- are vastly different in disparate parts of the globe. This heterogeneity of responses suggests that, on the whole, the planetary system would remain pretty stable -- or at the very least, global-scale changes will tend to be very gradual, rather than abrupt and catastrophic.

Reached as he was boarding a plane Friday morning, Anthony Barnosky, a professor of integrative biology at Berkeley and the lead author last summer's tipping-point study, suggested politely that the new analysis, which he had reviewed, was missing a fundamental point.

"Bottom line, they seem to not be taking into account that humans now connect all the ecosystems they are regarding as unconnected," said Barnosky, who argued that while local and regional ecosystems have always had, and still maintain, some variation in how they respond to similar environmental stressors, humans have come along and linked those ecosystems in novel ways.

Erle C. Ellis, an associate professor in the Department of Geography and Environmental Systems at the University of Maryland, Baltimore County, and a co-author of Thursday's study, acknowledged those new connections. But in an email message he suggested that the impacts remain varied from place to place:

Humans do move matter, energy and species across the planet, interconnecting ecosystems and populations like never before, and this does affect the biosphere. However, even when we move highly successful dominant species around -- like corn (maize) or kudzu (and other domesticates and other exotics), we find no evidence that this causes the entire biosphere to shift into a new state. Our effects on the biosphere are different everywhere (kudzu is not happy in the tundra, corn can't reproduce itself; we cut down trees in one region, they are regrowing in another, different areas respond differently to global climate change, acid rain, etc.) -- there is simply no evidence that these new global connectivities are causing a coherent or synergistic global response like a global tipping point.

Even global climate change does not have uniform effects on the terrestrial biosphere, Ellis said, and ecosystems respond differently to the same changes in climate. He pointed to "wetlands and deserts responding to increased rainfall, [or] tundra and forest responding to increased temperatures."

"There is no solid evidence that the entire biosphere is subject to a coherent tipping point interaction with the climate system," Ellis said.

Not everyone buys this. Michael E. Mann, the climatologist and director of the Earth System Science Center at Pennsylvania State University, called the new paper "thoroughly unconvincing and implausible."

"We are not talking about random uncorrelated changes around the globe," Mann said, pointing by way of example to human-induced climate change. "We are talking about dramatic, coherent changes in climate around the world, in the form of unprecedented rates of warming, increased continental drought, extreme flooding and wildfires. Moreover, these are not simply additive, but interactive, with a whole array of other stresses on ecosystems around the world due to urbanization and habitat destruction, deforestation and environmental pollution."

The totality of these stressors, Mann argued, is greater than the sum of its parts.

"It's part of why scientists are predicting a collapse of coral reef ecosystems around the world in a matter of decades -- the combined result of ocean acidification, global warming, coastal pollution, and other factors," he said. "I suppose the authors would deny that this represents a global environmental tipping point."

His skepticism was echoed by Paul R. Ehrlich, a professor of population studies in the department of Biological Sciences at Stanford University and president of the school's Center for Conservation Biology. Ehrlich, perhaps best known for sounding the alarm on the consequences of human population growth in the 1960s, said that while many of the finer points of the recent tipping-point paper were well-taken, the assertion that humans aren't likely to cause bedrock changes in the planetary system may be shortsighted.

"The ecosystems of different continents are intimately interconnected by climate, fugitive dust, toxins, and human activities and health -- think epidemics, resource wars (possibly turning nuclear) and so forth, and thresholds are typical of all of them," Ehrlich said. "I think one of the major failures of our communication with the public has been not to emphasize that in Earth's history, transitions have often been quite rapid."

If all this seems a bit academic, well, it is. But as both sides suggest, the debate bears significant implications for everyone, as the ledger of human impacts on the environment -- whether it's razing forests or killing off species or pumping planet-warming gases into the atmosphere -- continues to grow. Should there be a global tipping point out there, some line after which the whole planet breaks and loses the ability to sustain life as we know it, we'd surely not want to meet it.

"No one, of course, thinks it's a binary thing -- that you're fine one day and screwed the next," said environmental activist and climate action provacateur Bill McKibben. "But the evidence suggests that if big things happen, they can trigger other big things: The temperature warms enough and then you get a lot of methane and carbon released from the far north, for instance."

"One always hopes," McKibben said, "that the optimists will be proven right."

This post has been updated to add comment from James E. Hansen and additional comment from Erle C. Ellis.

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