‘Planetary Boundaries’ a flawed mechanism to safeguard Earth’s biodiversity, scientists warn

The notion that human impacts will be fine, so long as we keep them within “planetary boundaries,” is seductive but deeply flawed scientifically. Worse, though well-intentioned, it encourages harmful policies, three of the world’s leading ecologists argue in a peer-reviewed commentary published this month in Trends in Ecology & Evolution.

“A critical question is how should we manage human actions that harm the natural world,” said Stuart L. Pimm, Doris Duke Professor of Conservation at Duke University’s Nicholas School of the Environment. “Do we really want to operate under the assumption – as the notion of a planetary boundary for biodiversity purports – that humans can go about business as usual so long as the impacts of our actions remain within some arbitrary ‘safe operating space’?”

The concept of planetary boundaries is based on the idea that there are at least nine global processes that regulate the resilience and stability of Earth, and that human actions since the Industrial Revolution have become the main driver of change in each of them. “That’s true!” said Pimm.

Some have argued that when the impacts of human activities exceed a system’s boundary, or tipping point, there will be a precipitous and irreversible environmental change that could undermine Earth’s functioning and, ultimately, human survival. “That idea is certainly not true — at least with the global scope and ubiquity its originators propose,” Pimm argues. “It may be well-intentioned as an argument for limiting human impacts, but it’s alarmist and unhelpful to those who manage Earth’s natural resources.”

“The problem is that the notion of planetary boundaries for biodiversity adds no insight into our understanding of the threats to biodiversity and ecosystem functioning, and has no evidence to support them. It is too vague for use by those who manage biodiversity, and can promote harmful policies,” said lead author Jose M. Montoya, from the French National Centre for Scientific Research, at the Theoretical and Experimental Ecology Station in Moulis. “Take the boundary definition. The original idea was to use extinction rates. Certainly, there would be local consequences of species loss, but why a precipitous collapse of ecosystems,” Montoya asked.

Neither theory nor empirical data support any threshold of biodiversity below which ecosystem function is compromised, Montoya said. “Confronted with these fatal flaws to the original idea, there has been a proliferation of new indices. They add no useful insight. Even were we able to estimate the necessary numbers, the definition of the threshold is entirely arbitrary,”  he said.

Perhaps, though the planetary boundary framework might add no insights into what we know about global human impacts, then its practical utility to environmental managers justify it, the scientists said in a news release. “Fatally, the boundaries framework lacks clear definitions, or it has too many conflicting ones, does not specify units, and fails to define terms operationally, so prohibiting application by those who set policy or manage natural resources,” said Ian Donohue, from Trinity College, Dublin, co-author of the study.

National Geographic Voices interviews Stuart Pimm for more insights:

DB: You effectively say that the planetary boundaries notion is bad science and worse policy, that species extinction rates aren’t going to create tipping points and there is a huge moral hazard in claiming boundaries. Please explain that.

Stuart L. Pimm

SP: It’s such an appealing idea. So long as we keep human environmental impact’s within “planetary boundaries” we can have business-as-usual without jeopardising the ability of Earth’s ecosystems to recover. There are, goes the argument, “tipping points” beyond which we must not trespass for fear of rapid transitions to a world much less favourable to human existence than at present. Alas, all this is deeply flawed.

Undoubtedly, the idea was meant as a well-intentioned warning that we must limit human actions. Indeed, we must, for they cause harm to our natural world. As a consequence, we make our own lives — and those of generations to come — much poorer.

Alas, there is a powerful moral hazard in using tipping points. They create pernicious policies. It appeals to those interests that are indeed harming the planet and which wish to do so. After all, if the planet hasn’t collapsed yet, it must be OK to carry on!

If we suggest a catastrophe has happened and the consequences are not evident, then how will managers and policy makers trust the science we do? When bad science informs policies, its future credibility is compromised.

DB: You are not the first scientists to query the concept of planetary boundaries. Why have you decided to speak out now?

SP: As others have discussed an increasing number of technical issues with tipping points at the global scale, the idea’s originators have simply kept on stating the original ideas without considering the critiques and the consequences. We wanted to show that there’re huge risks in doing this.

DB: What new insights and technologies have become available — or may be emerging  — that will help us grasp a truly effective way to manage our civilization in a way that is ultimately in a long-term symbiotic relationship with the rest of Earth’s biodiversity?

SP: Environmental science can sensibly inform those who manage and set policies for the complexity that is nature. But we need targets that are simple, meaningful, and measurable. Last year, we reviewed 42 large organizations devoted to managing the global environment and their various aspirational targets. In particular, we applauded the Convention on Biological Diversity (CBD) and others when they define rigorous and operational targets. Good examples are 17 percent of land area and 10 percent of the ocean protected (CBD’s target 11), with the areas being “ecologically representative and well-connected”, “avoiding overfishing” (target 6), and preventing “the extinction of known threatened species” (target 12).

These are well-defined targets. Importantly, we can measure progress: look at how much of the oceans is now protected by efforts including National Geographic’s Pristine Seas, for example! Look at how many lions and other big cats have been saved by the National Geographic Big Cats Initiative.

DB: You’ve noted that ecology is rapidly gaining insights into the connections between biodiversity and ecosystem stability — and that humans have no option but to understand ecological complexity and act accordingly. Can you explain that a bit more?

SP: Environmental scientists must seek ways to engage policymakers to frame all their other aspirations similarly, because some are less tangible — “sustainability,” “health,” “harmony,” and others. They all speak to the urgent need to understand how human impacts change ecosystems. They all use terms that we group under the heading of “ecosystem stability.”

The challenge is to combine our increasingly good knowledge of how ecosystems work with these aspirations in ways that we can implement them to effect practical changes to save our global environment. We need to know the consequences of losing particular species, such as wild pollinators for our crops, or the removal of top-predators such as sharks from the oceans or wolves from the land. We need to understand which invasive species will cause most harm to natural ecosystems, for manifestly some are more harmful than others. We must ensure that fisheries and other exploited resources provide reliable yields against a background of year-to-year variability, given the economics that require a minimum annual return on investments. And so on.

Fortunately, mounting evidence demonstrates how biodiversity loss alters the provision of functions and the stability of ecosystems. We can now assess and monitor how losses in biodiversity affect different ecosystems. This, in turn, allows determining the effectiveness of a given environmental policy. The focus must be on appropriate scales and variables we can measure operationally and that tie to pressing practical problems.

CITATION: “Planetary Boundaries for Biodiversity: Implausible Science, Pernicious Policies”, Jose M. Montoya, Ian Donohue, and Stuart L. Pimm, Trends in Ecology and Evolution, online publication: 8-NOV-2017, DOI: 10.1016/j.tree.2017.10.004.

Stuart Pimm served on both the National Geographic Society’s Committee for Research and Exploration and the Society’s Big Cats Initiative. He is a regular contributor to National Geographic Voices.


    Duke University
    November 22, 8:36 am

    Dear Serge Michel — just great to hear from you again! Your comments are exactly on the mark. We agree there can be population thresholds. But importantly, we agree that the changes in fisheries are complex and they need understanding of the specific circumstances. Fisheries management is not well served by facile statements that everything was fine before 1990 and damned thereafter. As your final paragraph, we couldn’t have said it better ourselves.

  2. Serge Michel GARCIA
    Fiumicino, Italy
    November 14, 10:31 am

    We met Professor Pimmm in 1984 in a Dahlem Conferenz on the management of multispecies fisheries and this encounter marked my professional life. I am presently working on collapses and rebuilding of fisheries and one of the questions is: could over-intensive fisheries collapse an entire ecosystem? Well-managed fisheries use precautionary threshold levels in decision-making. The facts are that tipping.points probably exist at population level but their position is rarely known with precision. There are rule of thumbs, and fisheries try usually to stay away from them. In multi-species assemblages, changes are common, due to combinations of fishing and environmental factors, but tipping points become a lot more complicated to demonstrate and to link to clear causal factors, and major collapses of single fisheries have usually been due to a combination of too high fishing and bad environmental conditions. These oscillations, however, are not real collapses and are, to a large extent, part of the natural behaviour of the environment that need to be foreseen and accounted for in the precautionary management designs. Collapses at whole ecosystem level due to fishing have never been observed in large marine ecosystems (but large scale changes yes). The point is that as Prof. Pimms argues, they change, often in a not too abrupt way (they are surreptitious), with progressive changes in resources abundance and composition, , followed by changes in the fisheries using them, but these changes are not collapses as the ecosystem functions continue to be delivered, only differently.

    This does not mean probably that ecosystem collapses can be entirely ruled out, but precautionary rule is to keep these systems within known historical boundaries and a good dose of foresight and precaution are more useful and less risky than relying on unlikely global or regional tipping points.