In 2009, a team of prominent environmental scientists published a paper in Nature proposing that there were nine biophysical limits on human civilization beyond which there could be "consequences that are detrimental or even catastrophic for large parts of the world." They announced that "three of nine interlinked planetary boundaries have already been overstepped," injecting the issue with urgency. Planetary boundaries quickly became a paradigm célèbre, the subject of flattering coverage in the New York Times and Scientific American, and was embraced by both WWF and Oxfam. By last April, planetary boundaries had been included in the document being negotiated at this week's United Nations environment conference in Rio de Janeiro.
And yet, from the moment it was published, independent environmental scientists were leveling tough criticisms at the paper, publicly and privately. The supposed "biophysical boundaries" were, scientists pointed out, set subjectively. How much nature should we plow under for food and how much should we leave to animals? How much nitrogen fertilizer should we use? How much fresh water should we divert? These are subjective human choices, not ones that can be determined by ecological systems.
Moreover, scientists complained, the planetary boundaries authors were mixing up global issues like climate change with local issues. Climate change has real-world global thresholds, like melting ice sheets, whereas biodiversity and water, land and fertilizer use do not. China surely needs to -- the US gets the same high yields using a fraction as much fertilizer much per hectare. But that doesn't have anything to do with the need of African countries like Rwanda and Malawi for more fertilizer. for local environmental problems makes no sense.
Were the planetary boundaries authors suggesting that the Africans should wait to use more fertilizer until the Chinese had reduced their use? Not exactly. But in calling for cutting global fertilizer levels by 75 percent, the authors were clearly framing fertilizer as a problem of too much (e.g. in places like China), while leaving the problem of too little fertilizer (e.g., Rwanda) out of the framework.
The failure to account for different environments points to the main problem with the planetary boundaries framework: it only measures environmental change as negative -- as progression toward supposed biophysical boundaries -- and never as positive, either for humans (e.g., more food) or environments (e.g., higher yields resulting in less deforestation).
Early this month, the Breakthrough Institute published a report based on a thorough review of the literature that found little scientific support for the planetary boundaries hypothesis. We benefited from an informal review of each section by leading scientific specialists from the relevant fields. Thoughtful stories on the debate were filed by The Economist, Scientific American, and the Wall Street Journal. By late last week, United Nations negotiators had stripped out all references to planetary boundaries from the Rio+20 text.
There are useful implications for environmental change science that can be drawn from where planetary boundaries went wrong. First, any pragmatic framework on environmental change must look at benefits and costs. Some of the hypothesis's authors have said that their motivation was to provide a useful framework for helping global leaders manage environmental change. We applaud and support this motivation. But for any environmental change framework to be useful, it must seek to understand not only the costs of change but also its benefits.
One of the implications of this is that simply measuring variance from Holocene baselines is a highly misleading metric of human sustainability. Since so much variance from the Holocene has been good for humans, future environmental change cannot be assumed, as planetary boundaries does, to be negative for our welfare.
The same is true for environments. Too much fertilizer causes dead zones and other problems, but too little might result in lower yields and thus higher deforestation as humans convert forests into farms. Any framework seeking to understand the Anthropocene must illuminate, not obscure, these trade-offs. This is what the United Nations IPCC scenarios and many other environmental change frameworks attempt to do.
Finally, any framework seeking to describe environmental change must be transparent about its ethical commitments and worldview. Science can't tell us how much of nature should be plowed under, nor whether we should use more fertilizer or deforest more. Suggesting it can is to commit the sin of scientism -- conflating "what is" with "what ought to be."
One of the big initial criticisms of planetary boundaries made by scientists was that the numbers set were arbitrary. But all attempts to name a number will be, in an important sense, arbitrary, in that they will reflect preferred outcomes. For this reason, future metrics of environmental change must make the connection to particular human and environmental outcomes and values explicit.
The task for scientists and analysts must be to make clear the costs and benefits of environmental change. That means presenting not just one number but multiple numbers, and a transparent discussion of what they mean. Only when the trade-offs of environmental change, and the political and ethical implications of proposed limits, are made transparent, can a useful discussion of the ethics and politics of environmental change in the Anthropocene proceed.
-- Michael Shellenberger, Ted Nordhaus, and Linus Blomqvist, June 22, 2012