Walking the Line: How to Identify Safe Limits for Human Impacts on the Planet

PLANETARY BOUNDARIES: Can planetary boundaries help humanity manage its environmental impacts? Image: Courtesy of NASA

Is preserving the general environmental conditions that allowed civilization to flourish?a moderate climate, a rich array of species, rivers that reach the sea?necessary to ensure humanity endures? Or is minimizing alterations to the global environment introduced by human activity?rising levels of CO2 from fossil-fuel burning, widespread extinction, dams that impound water?more important to our success? Choosing the right approach is vital as the scale of human impact on the planet becomes so large that scientists are calling this new epoch in Earth's history the Anthropocene (when human activity alters global climate and ecosystems).

One bid for preservation initiated in 2009 by 29 scientists from around the world focused on the concept of planetary boundaries. They identified 10 environmental limits we might not want to transgress in the Anthropocene: aerosol pollution; biodiversity loss; chemical pollution; climate change; freshwater use; changes in land use (forests to fields, for example); nitrogen and phosphorus cycles; ocean acidity; and the ozone hole. That meme has now spread to the United Nations, and is driving ongoing global talks to address environmental problems, including the much-anticipated Rio+20 summit meeting that begins next week in Rio de Janeiro.

But a new analysis from environmental policy think tank the Breakthrough Institute released June 12 argues that such a focus on environmental restoration is actually counterproductive when it comes to overall human welfare. "The planetary boundaries framework is not a useful guide for policy or environmental management in any concrete sense, as it does not capture the challenges involved in most of the environmental problems it lists," argues geographer Linus Blomqvist, policy associate at the institute's Conservation Program and co-author of the review. "They should be discarded."

Specifically, Blomqvist and his colleagues argue that six of the 10 boundaries?land use, biodiversity, nitrogen cycle, freshwater use, aerosol and chemical pollution?do not have a hard limit at planet-scale physical thresholds that, if transgressed, would tip them into functioning differently. For example, managing a given watershed may make more sense than managing the amount of global freshwater consumption to stay below an arbitrary, sustainable "limit" of 4,000 cubic kilometers per year.

Further, breaking any of these boundaries might not have any negative impact on humanity. Indeed, cutting back on, say, nitrogen fertilizer could significantly set back human welfare given that more than half of the people on the planet are fed by food grown with synthetic fertilizer. A pristine rainforest, after all, provides less direct benefit to humanity than additional food production. Instead, society should focus on environmental trade-offs, the review argues. "The real limitations for sustainability are rather our ability to grow enough food, maintain a healthy climate and so on," Blomqvist says, although the analysis fails to offer its own limits or policy suggestions other than focusing more on climate change.

Reducing the emissions of the greenhouse gases that cause global warming makes the most sense in the context of planetary boundaries, and many of the other thresholds collapse into it, Blomqvist and his colleagues note. That makes climate change the defining boundary of the Anthropocene. "Arguably, the single most important measure to ensure climate stability is reform of our energy and transport systems," Blomqvist says. "There is every reason to regard the Holocene climate as desirable." (The Holocene epoch extends from about 12,000 years ago to the present.)

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