Planetary boundaries

Yet another unhelpful human construct?

In recognition of how human activities threaten irreversible environmental change, as observed in and enacted through planetary systems, Rockstrӧm et al propose a framework of boundaries and associated limits for nine key global subsystems that circumscribe a “safe operating space” for humanity. The theory is that so long as we remain within the limits of certain key thresholds, the biosphere is resilient enough that humanity will continue to enjoy the stability in temperature, freshwater, and biogeochemical flows that has experienced the previous 10,000 years of Earth’s history. It is this stability, referred to as the Holocene, that has enabled the singular development of human civilization. It seems ironic then that it is human activities post-Industrial Revolution that are poised to disturb planetary systems to the extent that all life is threatened.

Of the nine key global subsystems presented as planetary boundaries by Rockstrӧm et al, it is suggested that human activities have exceeded critical thresholds for three: climate change, biodiversity loss, and the nitrogen cycle. This suggestion is supported by research, modelling, and the following (undeniable) observations: extreme climactic events, a rate of extinction comparable to the last global mass extinction events, and large-scale anoxic events. For all three of these boundaries, only proxy variables were available:

  • Atmosphere CO2 concentration and change in radiative forcing instead of long-term weather statistics.
  • Rate of extinction instead of a measure of biodiversity (loss).
  • Amount of N2 removed from the atmosphere for human use instead of a more complete picture of how human activities have affected the distribution and speciation of nitrogen

Compounding the unhelpfulness of the metrics available is how the planetary boundaries framework misrepresents planetary functioning. Both planetary systems described by the boundaries and the human activities that have disturbed those planetary systems are part of the same complex and dynamic system. Instead of considering metrics that represent the complex and dynamic system, the planetary boundary framework presents discrete benchmarking on a category-by-category basis. This benchmarking gives the mistaken impression that planetary subsystems can be disaggregated and that human activities have affected different subsystems differently. In actuality, the same set of human activities have been a participant component of the biosphere, and what we’ve observed is self-regulation of the system as manifested by different subsystems, rather than self-regulation within the subsystem itself.

An alternative framework is presented, and then bypassed, by the authors in the introduction. The root cause of humanity’s negative impact on Earth is identified: “a rapidly growing reliance on fossil fuels and industrialized forms of agriculture.” From this clear and concise evaluation of the foundational problem, the planetary boundary framework is then elaborated to visualize how this problem impacts different global subsystems. Does this framework then disaggregate measurement of one problem into nine discrete sectors, and to what effect? Is the planetary boundary framework effective, and if yes, why?


Rockstrӧm et al (2009). A safe operating space for humanity, Nature 461, 472-475.