Planetary Boundaries: Have We Crossed the Line?

      In one of my recent lectures a concept was discussed; that of Planetary Boundaries, and what use they can be. The study by Rockström et al., 2009b, entitled 'Planetary Boundaries: Exploring the Safe Operating Space for Humanity', in a sense summarises humanity's current impact on aspects of the Earth. Despite now being a few years old, and despite it's relevance to my interests and this blog, I had never seen this topic being discussed in this way. I thought it might, however, help readers to visualise impacts and figures that are mentioned in this blog.

       The concept is based on the idea that human actions have become the major factor of environmental change, and that once human activity causes certain environmental categories or processes to cross particular thresholds, the Planetary Boundaries, we risk possible catastrophic planetary change being triggered. This means the more lines we cause the planet to cross, and the further they do, the more likely we will so damage the Earth that humanity can no longer operate. The paper advises we define and respect these parameters to remain in "a safe operating space for humanity."

        Rockström et al., 2009a&b, go on to discuss the 9 specific environmental processes they deem of greatest importance, which each have a determined value set at a safe distance from a dangerous level, or an intrinsic threshold (such as temperature and ice-albedo feedback with preserving sea ice). A follow-up paper (which is much easier to read!), titled 'How Defining Planetary Boundaries Can Transform Our Approach to Growth', by Steffen, Rockström and Costanza, 2011, more obviously define these boundaries and their usage as in the table below.

The 9 processes and each of their boundaries defined, as in Rockström et al., 2009a, and Steffen, Rockström and Costanza, 2011, with the table obtained from the latter.

       The problem is, as both papers note, we have already surpassed 3 of the 9 category boundaries - namely those of the Nitrogen Cycle, Climate Change (based on carbon dioxide concentrations and radiative forcing change), and most significantly Rates of Biodiversity Loss (by the huge increase, and its relevance to this blog!). While the other two crossed boundaries are clearly important, biodiversity loss by increased extinction rate is an estimated more than 10X higher than the safe limit, and 100-1000X (+) higher than the pre-industrial value (similar to a 'background extinction rate')! By the findings of these papers humans are clearly having a devastating effect on biodiversity loss, and therefore ecosystem functionality (I will discuss implications of loss in later posts). This is visibly shocking when represented by a diagram:

The 9 Earth processes, with the cones representing the Earth's current position, and the globe  the boundaries for each. Clearly we are in the 'danger-zone' with all 3 red/orange processes, but biodiversity loss is hugely above safe levels. Diagram from Rockström et al., 2009.

       The purpose of this type of quantification on protecting the planet is towards a new approach in understanding, measuring and tackling global sustainability, before the Earth is irreversibly damaged. The concept gives a necessary framework to a complicated, significant and wide topic that is increasingly in need of organised action to combat the effects of environmental change.

       However, there are important issues associated with the Planetary Boundaries concept, and thus the papers themselves, including:

• As Steffen, Rockström and Costanza, 2011, discuss, there would need to be changes to governance and the creation of an authoritative institution to ensure the boundaries are respected. 
• In this same vein, it would be hard to enforce the strict controls that would be needed, particularly in disadvantaged countries.
• The definitions of the actual boundaries are at present markedly arbitrary, and are still uncertain, therefore require a great deal more work to be definitive. For example, extinction rate for biodiversity loss is extremely difficult to calculate (as discussed in a previous post); it must be done through assumptions and extrapolation, and therefore cannot be entirely relied upon. 
• Not all processes could even be assigned a boundary - it was not known how to calculate even an uncertain boundary for Chemical Pollution or Atmospheric Aerosol Loading.
• The papers point out that the authors are not sure 9 boundaries are sufficient to define planetary sustainability; this year Steve Running, and Kate Raworth (Oxfam) both suggested other boundaries should be included [4].

       The fact that this concept is being debated and discussed is nevertheless an important step towards understanding the complexities of Earth-system science, the impact humans have on the planet, and the possible consequences this can have on other species, and our own.

If you want to read more, but less confusing, detail about the Planetary Boundaries, you could head over to the page on Wikipedia, which also contains a list of additional commentary and other papers on the subject.

References:
1. Rockström, J. et al., 2009a. A Safe Operating Space for Humanity. Nature, 461, 472-475.
2. Rockström, J. et al., 2009b. Planetary Boundaries: Exploring the Safe Operating Space for Humanity. Ecology and Society, 14: 2.
3. Steffen, W., Rockström, J. and Costanza, R. 2011. How Defining Planetary Boundaries Can Transform Our Approach To Growth. Solutions Journal, 2: 3.
4. Wikipedia, 2012. Planetary Boundaries. <http://en.wikipedia.org/wiki/Planetary_boundaries> First accessed 28/10/2012. [WWW].