Planetary Boundaries: Re-visited

      A couple of weeks ago I posted on the Planetary Boundaries concept, devised by Röckstrom et al., 2009, which attempted to define limits of nine environmental categories of such importance that crossing them risks such catastrophic, irreversible change to the planet so that Humans can no longer survive. The reason for focusing on this study was that we have already dramatically crossed the biodiversity (extinction rate) threshold, however there has been a great deal of recent debate over the concept.
  
     Numerous other papers have been published this year exploring or supporting Röckstrom et al., 2009; for example Barnosky et al.,2012; 'Approaching a state shift in Earth's biosphere', in Nature. This reiterates the points made by Röckstrom et al., 2009; that critical transitions caused by threshold crossings are likely, it is human forcing mechanisms that cause this (human population growth, resource consumption, habitat degradation, climate change etc.), and that past events (particularly slow recovery after extinction events) show how serious this can be. The paper also concentrates on the way these thresholds are tracked, and the evidence for climate trends along with this concept.

Potential drivers of critical transitions across planetary boundaries: a=fragmenting landscapes, b=indirect changes, c=accumulation of change to the Earth's surface, showing 40% are now agricultural areas, d=accumulation from pollutants, e=release of greenhouse gases changing ocean/atmospheric chemistry, f=changing seasonal temperatures, g=changes to reservoirs of biodiversity by species introduction and climate change, h=global trend to warming and ice melting. From Barnosky et al., 2012 (fig.1).

'Earth May Reach Tipping Point'; Barnosky, A.D., 2012. UC Berkley.

   
       However, several other recent papers hotly dispute the concept - such as a report by Shellenberger et al. (Breakthrough Institute), 2012, which states the idea "has serious scientific flaws and is a misleading guide to global environmental management", and is "a poor basis for policy and for understanding local and global environmental challenges." Key findings in their assessment of the planetary boundaries hypothesis are:

• That six of the nine planetary boundaries do not have specific global thresholds in themselves - i.e. land-use change, biodiversity loss, nitrogen levels, freshwater use, aerosol loading and chemical pollution have no actual global tipping points beyond which these processes function in entirely different ways than they do now or have historically. This makes the setting of these boundaries particularly arbitrary - crossing the thresholds may have no affect; they don't help us understand possible results.
• Aside from the effects on global climate, the above six boundaries operate on local and regional scales, not globally - changes to these and what they can cause in some areas are independent of their processes in other regions (e.g. land-use change).
• There is little evidence to support the idea that transgressing these six boundaries would have a net negative effect on human welfare - net benefits and costs vary with locality, economic position etc.
• Lewis' column in Nature commenting on planetary boundaries (2012) also believes the idea isn't defined enough to be of use - he states that there should be a distinction between thresholds, as some are true lines that we can cross, whereas other categories have fixed limits (like Phosphorous-use) that we cannot cross. This might change the way we act on the process; preventing its impact on the environment, but harming our own systems like food production by not noticing all the angles. However, Galaz, 2012 does dispute Lewis' contentions.
• There have been several papers and letters exploring problems with specific planetary boundaries, which are too detailed to go into here. The individual thresholds can be researched to read more on the justifications, or lack of evidence, for them; for example Allen's commentary from 2009 in Nature Reports on the Carbon Dioxide limits.

      It could be said that regardless of this the concept is important in directing thinking and action in sustainability; I do believe this to be true, as it does provide a useful framework for further research. However, as the Shellenberger et al., 2012, report notes, using an idea fraught with issues as a basis for policy can lead to more miss-led action and confusion, such as:

• Specifying regional processes as global may negatively affect local-level policies, due to the trade-off between positive and negative impacts on welfare.
• Most of the six non-threshold boundaries integrate with climate change; assigning them all as different boundaries is likely necessary, but confuses the causes and effects of one of the largest global processes.
• Ecological degradation so far has shown little correlation with specifically human material welfare.
• The limits and crossing of them do not necessarily need 'fixing' as the concept implies, but more balancing with human welfare needs - there will be various courses of action and trade-offs that cannot here be explored.
• Lewis, 2012, believes all government bodies focusing on all the nine planetary boundaries could spread political will too thinly. He states that those affected by regional problems should instead work to solve these, and global combined efforts should focus on those clear global changes of climate change, biodiversity loss and ocean acidification.

     An article from July 2012 in The Economist provides a useful summary of the current aspects of this debate, and whether the concept of planetary boundaries is still useful. It uses a strange but apt metaphor to explain the thoughts of those supporting its application:
        "PULL a spring, let it go, and it will snap back into shape. Pull it further and yet further and it will go on springing back until, quite suddenly, it won't. What was once a spring has become a useless piece of curly wire. And that, in a nutshell, is what many scientists worry may happen to the Earth if its systems are overstretched like those of an abused spring."

The idea has clearly taken root, despite some objections, as it has even been used in many political conferences on sustainability. I do see the merit in the criticisms above; clearly if a system such as this is to be used for policy-making and action on such an idea as possible catastrophic environmental change there should be more defined, less abitrary, limits put in place. As human action tends to be a balancing act, great care should also be taken when using this to advise. However I do see this basis could be of importance once developed, and is worth the further debate.