Credit: DonkeyHotey, from a NASA image, CC BY 2.0

Much of today’s discourse about environmental problems revolves around the need to reduce greenhouse gas (GHG) emissions. But that’s not nearly enough, according to Johan Rockström, director of the Stockholm Resilience Centre at Stockholm University.

The Earth is facing environmental tipping points along what Rockström calls planetary boundaries, which revolve around not just climate change, but also stratospheric ozone, biodiversity, chemicals dispersion, ocean acidification, freshwater consumption, land system change, nitrogen and phosphorus discharge and atmospheric aerosol emissions. These boundaries represent load-bearing limits on human activity.

In New Perspectives Quarterly (“Planetary Boundaries,” Winter 2010), Rockström wrote:

In order to avoid catastrophic tipping points, we need to effectively manage key Earth system processes, and we need to do it now … Whether or not humanity will be able to stabilize climate within safe levels depends upon our ability to reduce emissions and constructively manage a number of critical natural systems on the planet … Unfortunately, in this drama there are no second chances. Nature does not do bailouts.

Rockström and a group of scientists introduced the term “planetary boundaries” in 2009, in an article in Ecology and Society (“Planetary Boundaries: Exploring the Safe Operating Space for Humanity,” Vol. 14, No. 2). Since then, the concept has been embraced by the United Nations, Oxfam, the WWF and other groups. Some observers expect the planetary boundaries model to play an important role at the UN Conference on Sustainable Development (also known as the Rio+20 meeting), June 20-22.

Not all are thrilled with the planetary boundaries model, however. Critics make the point that while some of Rockström’s boundaries are real thresholds with real limits, others are not true limits with definite consequences. Trying to establish global restrictions based on these purported boundaries might actually inhibit the necessary give-and-take process of policy-making and might impose unnecessary and harmful restrictions on human development.

Planetary Boundaries: Maintaining
Holocene Climatic Conditions

Credit: Steve Swayne, CC BY-SA 2.0

Rockström’s planetary boundaries hypothesis is based on the idea that humanity has been able to flourish during the stable conditions on Earth of the last 10,000 years, a period known as the Holocene epoch. Human society needs to make sure those stable biophysical conditions don’t get disrupted.

The Ecology and Society paper outlined a series of systems and processes and attempted to quantify the appropriate boundaries of human development and maintain a “safe operating space for humanity.” As complex adaptive systems, the scientists believed, Earth systems have “tipping points.” Exceeding those tipping points could cause an exponential change in the Earth’s environment and endanger human welfare.

For example, if Earth’s climate warms too much, say by 2 degrees Celsius, the danger is that the climate could flip into a new state and result in a runaway greenhouse effect and catastrophe.

The paper’s authors attempted to quantify the boundaries for avoiding “unacceptable environmental change.” Three of the the boundaries, climate change, biodiversity loss and global nitrogen, have already been crossed. Freshwater use, ocean acidification and global phosphorous are close. Boundaries for aerosol loading and chemical pollution remain undefined, and land use change is seen as something that ought to have limits but has no natural boundary or tipping point.

Space Shuttle Endeavor straddles the stratosphere. Credit: NASA

Rockström acknowledged that the authors’ proposed boundaries “are rough first estimates, surrounded by large uncertainties and knowledge gaps,” and stressed that “filling these gaps will require major advancements in Earth system and resilience science.” That said, they did propose specific limits for seven of the planetary boundaries:

• Climate change. Limit CO2 concentration in the atmosphere to less than 350 parts per million or a maximum increase of one watt per square meter in radiative forcing.
• Ocean acidification. Hold seawater saturation with calcium carbonate to 80 percent or higher compared with pre-industrial levels.
• Stratospheric ozone. Maintain less than 5 percent reduction of ozone from the pre-industrial level of 290 Dobson units.
• Biogeochemical nitrogen cycle. Limit agricultural and industrial nitrogen fixation to 35 teragrams per year.
• Phosphorous cycle. Limit annual inflow of phosphorous to the ocean to 10 times its natural background weathering.
• Global freshwater use. Hold consumption to less that 4,000 cubic kilometers per year of runoff.
• Land use change. Maintain less than 15 percent of ice-free land under cultivation (currently 12 percent).
• Biodiversity loss. Hold annual rate of extinction to less than 10 species per million.

Is Planetary Boundaries
An Arbitrary Exercise?

Simon L. Lewis, a researcher of global change science at the University College London and the University of Leeds, wrote in Nature that the planetary boundaries concept is useful, but if it is misapplied, it could “shift political focus to the wrong areas.”

Some of Rockström’s boundaries, according to Lewis, are not just thresholds or ideal parameters but are actual hard limits. Take phosphorous, for example, a key plant nutrient that “forms on geological time scales” and has absolute limits. Once it’s gone, it’s all gone. Lewis wrote:

To highlight a boundary on phosphate pollution, for example, would drive investment in technology to combat the impact on marine environments but do nothing to stop the running down of rock-phosphate supplies. To emphasize the depletion limit would shift the focus to technology to use and re-use phosphorus to safeguard stocks.

A similar limit applies to plant growth, also known as terrestrial net primary productivity (NPP). Only so much plant growth can take place on Earth; it’s a hard limit. Never-ending increases in cropland aren’t feasible, according to Lewis:

Despite massive agricultural expansion in the past century, global NPP has not dramatically increased. It is a ceiling limit. Thus, the allocation of NPP to benefit biodiversity or food, fiber, fodder and fuel for humans is essentially a zero-sum activity.

 

Credit: anemoneprojectors, CC BY-SA 2.0

Another weakness in the model has to do with scale. The planetary boundaries are formulated according to global threshold numbers. Many problems are regional, though, and should be handled at the regional level rather than at the global level to avoid unnecessarily protracted conflicts and negotiations.

Lewis warned that “a simple transfer of a neat scientific idea into the policy arena could cause as many problems for policy makers as it solves.”

A report from the Breakthrough Institute, by Linus Blomqvist and colleagues (“The Planetary Boundaries Hypothesis: A Review of the Evidence,” June 2012), criticized that “six of the ‘planetary boundaries’ — land-use change, biodiversity loss, nitrogen levels, freshwater use, aerosol loading and chemical pollution — do not have planetary biophysical thresholds in themselves.” For these “boundaries,” according to Blomqvist, “there are no global tipping points beyond which these ecological processes will begin to function in fundamentally different ways than they do at present or have historically. Hence the setting of boundaries for these mechanisms is an arbitrary exercise.”

Also, these non-threshold benchmarks operate primarily on local and regional levels, so really no meaningful global boundaries can be established, the paper argued. Blomqvist said “there is little evidence to support the claim that transgressing any of the six non-threshold boundaries would have a net negative effect on human material welfare.” Such effects can be negative in some respects and positive in others, negative in some geographic areas and positive in others. “Specifying regional and local systems as global may, in many cases, result in misguided policies at the local and regional levels,” he reported.

The report cited the example of synthetic nitrogen fertilizer. In some regions, limits on nitrogen might make sense, decreasing groundwater pollution and dead zones in coastal ocean waters. However, setting global legal limits on nitrogen could have adverse effects in some regions:

At the same time, there are other areas, notably many parts of Africa, where increased use of nitrogen in agriculture would yield very significant benefits for human welfare. Moreover, limiting nitrogen use in Africa would in no way mitigate the impacts of excessive nitrogen use in other regions. As such, the positing of a global boundary is of little use to policy makers in either those regions that underutilize nitrogen fertilizers or those that overutilize them.

Credit: Horia Varlan, CC BY 2.0

Blomqvist also questioned the idea of boundaries for nitrogen, land-use change and freshwater use as they relate to climate change. According to him, such factors do affect GHG levels and thus impact climate change, but that “does not mean that there is any absolute boundary for them.”

The climate of the Holocene period has definitely been conducive to human welfare, he noted, but other than climate, he said there is no proof that Rockström’s other conditions are particularly important. He said, “While there are, of course, very good reasons to prefer the climate of the Holocene, which was relatively warm and stable, there is little evidence that land cover, nitrogen levels, biodiversity or any of the other non-climate systems had in themselves a stability or level that was particularly beneficial for human development.”

The report contended that empirical evidence does not support the “claim that the planetary boundaries represent ‘non-negotiable’ limits upon human activities, development or consumption.” While science is valuable in understanding the constraints on human activity, the report asserted that “there are multiple costs and benefits of human impacts on the environment, and that balancing these is an inherently political question.” Trying to impose strict global limits really inhibits debate and decision-making and narrows the range of available choices for policy makers. Developing policy requires examining costs and benefits, making tradeoffs, according to Blomqvist. He wrote:

A more constructive function of global change science would therefore be … to identify and explicate these trade-offs, in order to usefully inform the public, decision makers and interest groups about possible courses of action and their implications and thereby facilitate deliberative decision-making.

The planetary boundaries hypothesis stresses that the changes that human society are transitioning the Earth from the natural conditions of the Holocene to a new epoch called the Anthropocene, in which planetary systems are increasingly shaped by human activity. Rockström and colleagues believe the planetary boundaries proposition forces policy makers to consider a crucial issue, writing:

The Anthropocene raises a new question: “What are the non-negotiable planetary preconditions that humanity needs to respect in order to avoid the risk of deleterious or even catastrophic environmental change at continental to global scales?”

The Rio+20 conference this month promises to shine the spotlight on that question.

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