Although the 2009 study's authors also noted no thresholds exist for some of their planetary boundaries they proposed limits on land-use change, freshwater, nutrients and biodiversity based on two criteria. First, they help determine the resilience of ecosystems on land and at sea, which in turn impact whether larger boundaries, such as climate change, are transgressed. Second, they are associated with tipping points at the local scale. After all, when a large enough number of local ecosystems transform, a global shift occurs, notes Johan Rockström, one of the authors of the planetary boundaries concept and a natural resource management professor at Stockholm University.
"It would be good to define planetary boundaries at multiple scales—local, regional and global," adds ecologist Jonathan Foley, director of the Institute on the Environment at the University of Minnesota and a co-author of the planetary boundaries concept. But "if there are major changes in the global environment, beyond what we have experienced in the Holocene, then this could represent a serious disruption to our civilization."
Many of the criticisms offered by the Breakthrough Institute were raised in the original paper that presented the planetary boundaries concept, published in Nature on September 24, 2009. (Scientific American is part of Nature Publishing Group.) Blomqvist concedes that point, yet he says: "Given the sometimes naive reception of the [planetary boundaries] concept, we thought it was worthwhile pointing out."
Other scientists have criticized the planetary boundaries as too generous (for example, allowing too much human appropriation of freshwater flows) or employing the wrong metric (atmospheric concentrations of CO2 rather than cumulative emissions of greenhouse gases).
At the same time any effort to identify a safe operating space for humanity must grapple with the fact that humans, on the whole, have never been better off—whether the metric be population, wealth or some other measure. Any ecological degradation has not led to a collapse in human welfare.
The point of the planetary boundaries, according to its authors, is to enable an enduring human prosperity that doesn't destroy the planet's natural resources in the process—ultimately undercutting that good fortune. After all, the present wealth and attendant short-term boost in population, consumption and technological growth may be largely founded on longer-term deterioration of the planet, including declining fish populations, acidifying oceans, degrading soils, remnant forests, polluting watersheds and a transforming climate. "Future generations will pay the price for this," Foley argues, unless human activity is redirected. "I'm still hopeful that we can do this, but it will represent a massive shift from our current way of running the world."
Blomqvist agrees: "We must not destroy the ability of future generations to enjoy a healthy, good life by depleting resources for short-term gain." In addition, he says, "humans everywhere want food as well as beautiful landscapes and a rich biological heritage."
The difference in approach comes down to how best to manage the Anthropocene: through planetary boundaries suggested by the environmental systems that allowed the epoch to come about or through local or regional efforts aimed at weighing the complex trade-offs among human resource use, ecological needs and a global push to combat climate change. "Arbitrary boundaries are not helpful and, if anything, can be dangerously misleading on local and regional levels," Blomqvist maintains. And "critical transitions" or "tipping points" as suggested by the planetary boundaries concept may not exist for many of the cases because those shifts, if they exist, have already happened. "Earth has already been fundamentally and thoroughly transformed by humans," Blomqvist notes. "Saying that land-use change has a tipping point in this respect is like saying that there's a tipping point for methane-farting cows."