The potential role of the planetary boundary for biosphere integrity
The planetary boundary framework was originally developed to identify the key global processes that are essential for regulating the functioning of the Earth System and create what are effectively safe ‘buffer zones’ that might prevent humanity from crossing dangerous biophysical thresholds or tipping points. In its current version, the framework describes nine such boundaries, ranging from climate change to atmospheric aerosol loading and including freshwater use, land-use change, stratospheric ozone depletion, introduction of novel entities to the environment, ocean acidification, biogeochemical flows and, crucially, biosphere integrity. The fact that the boundaries represent the limits of what the authors call the ‘safe operating space’ for human development on a changing planet has attracted immediate interest from political scientists working on Earth System governance, and some legal scholars have progressively started to consider the concept as potentially useful for international environmental law as well.
Ever since the first elaboration of the nine planetary boundaries, the very possibility of identifying a global boundary for biosphere integrity resulting from changes in regional and local biodiversity has appeared as one of the most contentious aspects of the framework. As a result of intensive discussions to which various research communities contributed, the description contained in the original planetary boundaries paper was in fact updated in 2015,in order to capture the two key roles of the biosphere in the Earth System, and namely: (a) the importance of genetic diversity in maintaining and building its resilience (i.e. through the use of global extinction rates); and (b) the contribution of organisms’ functional traits to Earth System functioning (i.e. through the so-called Biodiversity Intactness Index). In doing so, the planetary boundary framework was also expanded to recognize the importance of sub-global boundaries that must align with the global boundary definition for biosphere integrity, owing to the fact that the ideal unit of analysis for changes in elements of biodiversity is usually situated at the level of biomes and ecosystems.
From this perspective, and subject to further scientific advancements and new data becoming available, a planetary boundary for biosphere integrity could potentially represent a very useful tool for international biodiversity law. On the one hand, because the national allocation of the planetary ‘safe operating space’ would recognize and make explicit the above-mentioned link between a global boundary and the regional, national and sub-national operating scales at which biodiversity loss occurs. On the other, and as a consequence, because the incorporation in international biodiversity law of a global boundary that might be quantifiable through critical values for one or more control variables could in theory enable changes to biosphere integrity to be used as an indicator of State responsibility, providing a powerful empirical benchmark against which to assess the respect of legal obligations relating to biodiversity (or, at the very least, a set of more precise, science-based objectives and targets that it would be more difficult for States to ignore).
The nine planetary boundaries and the status of their control variables. Source: Steffen et al. (2015)
For the purpose of the present analysis, it is less important what the control variables should be, and it should indeed be noted that identifying suitable ones for biosphere integrity remains a daunting and still hotly debated task. What is crucial is that the concept of a measurable planetary boundary for biosphere integrity clearly suggests that the related biophysical limits, once incorporated in international law, could play an important role in mitigating the procedural and/or non-enforceable nature of most international obligations relating to biodiversity within national jurisdiction (for example, the requirement to develop national strategies, plans or programmes for the conservation and sustainable use of biodiversity set in Article 6(a) of the CBD, or the obligations for in-situ conservation listed in Article 8).