Planet Earth

Advancing the Planetary Boundaries Hypothesis

Collide-a-ScapeBy Keith KloorJun 13, 2012 4:54 PM

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For decades, environmentalists and many earth scientists have been warning that humans are exceeding the earth's carrying capacity, that our numbers (7 billion and counting) and the way we farm, fish, and live is overwhelming the ecosystems we depend on. In 2009, Johan Rockström and two dozen colleagues proposed

a new approach to global sustainability in which we define planetary boundaries within which we expect that humanity can operate safely. Transgressing one or more planetary boundaries may be deleterious or even catastrophic due to the risk of crossing thresholds that will trigger non-linear, abrupt environmental change within continental- to planetary-scale systems.

When the planetary boundaries concept was published in Nature, it was immediately recognized as controversial. "The new paper has already drawn strong reactions from other scientists, some glowing, some harsh," wrote Carl Zimmer in Yale Environment 360. An accompanying editorial in Nature described the paper as "a creditable attempt to quantify the limitations of our existence on Earth," but also noted:

For the most part, the exact values chosen as boundaries by Rockström and his colleagues are arbitrary. So too, in some cases, are the indicators of [environmental] change...Furthermore, boundaries don't always apply globally, even for processes that regulate the entire planet. Local circumstances can ultimately determine how soon water shortages or biodiversity loss reach a critical threshold.

Nature made sure to include commentaries from scientists not involved with the paper, whose expertise enabled them to address specific aspects of the planetary boundaries proposal. The respondents had their own quibbles, but overall they found the framework useful. Since 2009, the major themes laid out in the planetary boundaries proposal have been the subject of high-profile symposiums and institutional reports on the state of the earth. See, for example, the recent Planet under Pressure conference, which declared that "the continued functioning of the Earth system..is at risk." In April, the UK's Royal Society released it's much discussed report that said humanity would continue "to drift into a downward spiral of economic and environmental ills," unless global population and consumption rates were curtailed. In case you weren't getting the picture, last week Nature published another big paper on global ecological trends that warned of a "planetary-scale tipping point," due to, as the University of California press release said, "population growth, widespread destruction of natural ecosystems, and climate change." Those of you not yet in a fetal position, whimpering "please, no more," might want to sing along to this classic. Or, if you're a glass half full kind of person, you may want to check out some fresh new critiques of the planetary boundaries concept. There is a slew of them that, taken together, offer a counter-narrative to the one that I just chronicled. Let's start with Erle Ellis, a geographer at the University of Maryland, and his essay in the fall issue of the Breakthrough Journal:

The "planetary boundaries" hypothesis asserts that biophysical limits are the ultimate constraints on the human enterprise. Yet the evidence shows clearly that the human enterprise has continued to expand beyond natural limits for millennia. Indeed, the history of human civilization might be characterized as a history of transgressing natural limits and thriving. While the Holocene's relatively stable conditions certainly helped support the rise and expansion of agricultural systems, we should not assume that agriculture can only thrive under those particular conditions. Indeed, agriculture already thrives across climatic extremes whose variance goes far beyond anything likely to result from human-caused climate change.

Ellis is also a contributing author of an essay in the June issue of Bioscience which aims to stake out a middle ground between two poles: The Limits to Growth mentality (which clearly underlies much of the gloomy aforementioned assessments) and the don't worry, human ingenuity will come to the rescue mindset. The former attitude can't feasibly address the needs of the developing world and the latter attitude ignores the legitimate and mounting ecological stresses on the planet. Ellis and his fellow Bioscience authors write:

We assert that an emphasis on global biophysical limits at the expense of a focus on realistic solutions is insufficient, as are assumptions that technologies can always solve environmental problems.

Instead, they suggest that for scientists to be truly relevant,

a vision of planetary opportunities needs to become a focal point for global change research, with sophisticated exploration of the synergies and tradeoffs between human and biophysical systems that will ultimately determine the success of our species and our planet's ecological heritage.

This notion of tradeoffs is at the heart of a new report just released by the Breakthrough Institute (TBI), which argues that the planetary boundaries framework "has serious scientific flaws and is a misleading guide to global environmental management." Their conclusion is based on an "extensive literature review" of the science underlying the 2009 Nature paper. It's worth pointing out that neither TBI's report or the Nature paper were peer reviewed. A judgement of TBI's assessment is beyond the scope of this post. I'd have to invest many, many hours cross-checking studies and following up with researchers. I'm hoping that some of my colleagues staffed at news outlets will take the time to drill down into TBI's claims. What I can say is that I've read their report, reread the Nature paper it is critical of, as well as other related publications. I've also reached out to Jon Foley, a University of Minnesota earth scientist, who was a contributing author of the 2009 Nature paper. Foley, on Twitter, and in an email exchange, has been dismissive of the TBI report. He says it is "poorly thought out, and doesn't say anything especially useful or new." He also asserts that the TBI report "mischaracterized the original PB [planetary boundary] study, and ignored what many other people (including us) had said before." Here, Foley is referring to previous critiques made of the planetary boundary framework in that collection of Nature commentaries I mentioned earlier, as well as the hedging and qualifications made in the original Nature paper, which did candidly admit: "The knowledge gaps [in assessing biophysical limits] are disturbing." (Just as an aside, Foley and his Nature co-authors have been similarly accused of not paying sufficient tribute.) At this point, the average reader can get lost in the weeds, trying to sort through the various claims and counter-claims. But what I have noted about Foley's rebuttal is that, while sweeping, it doesn't specifically address the case that TBI has mounted against the scientific foundation for the planetary boundaries, or some of the flawed assumptions that TBI asserts the concept is is based on. Based on my reading of the report and exchanges I had with its lead author (and TBI Research Associate), Linus Blomqvist, I'm seeing issues raised that are worthy of debate. Here is Blomqvist, in an email to me, explaining what he sees as the bigger picture:

Environmental management tools and concepts must be adapted to the practical reality of the environmental problems it addresses. By trying to fit too many environmental variables in the same framework of boundaries and tipping points, PB [planetary boundaries] lost connection to actual on-the-ground challenges. For example, a single boundary cannot capture the fact that in some regions, increased nitrogen use, freshwater use, and perhaps even land-use change could benefit people, whereas in other regions the opposite is true. So for nitrogen the real challenge is to apply an adequate level to each field: enough to provide high yields, but not excessive in a way that causes negative side-effects. Both positive and negative impacts of environmental change on human welfare must be recognized. The truth is that increased nitrogen use, freshwater use, land-use change, and other human impacts on the environment have historically brought huge benefits for human material welfare. Policies that ignore these positive benefits and only see environmental change as negative are misleading. Linkages between environmental change and human welfare in policy frameworks like planetary boundaries are all too often just implicit assumptions that are based on aesthetic preferences for non-human nature rather than any empirical ground. This, I would say, is the most pressing weakness in most of environmental science today - it really is time to build a transparent, scientifically sound, and empirically grounded body of knowledge on the linkages between environmental change and human material welfare, in which aesthetic and material aspects are distinguished as clearly as possible.

Foley, being a self-described pragmatist, would be an ideal person to engage these points. In doing so, he could help design a revamped planetary boundaries framework, one that reconciles value judgements and real world tradeoffs with science.

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