Chemicals and Planetary Boundaries

Background

The Planetary Boundary Concept

The world is facing the triple planetary crises of climate change, loss of biodiversity and rising chemical pollution (UNEP 2021). Environmental scientists and members of civil society have been raising these concerns for decades with varying degrees of response. One concept that has “stuck” is that of Planetary Boundaries (PBs) which was first introduced by Rockström et al. in 2009 (the paper is cited over 10,000 times). PBs express a ‘safe’ limit beyond which the Earth’s biophysical systems could shift to a radically different state, away from the stable Holocene conditions that have enabled the development of, and have sustained human societies. The message from the PB analysis is that human societies need to transition from our current harmful practices so that we can stay within the PBs or the “safe operating space” to avert profound changes to the Earth’s biophysical systems, and hence the conditions that support contemporary human societies. For some PBs, notably climate change, the concept is tied to that of tipping points which are thresholds or points at which a system could irreversibly shift to a different state (Lenton et al. 2023).

As noted above, the concept has captured the imagination of the public, politicians and policy makers, perhaps because it conveys the urgency of the planetary crisis in a form that is conceptually simple and comprehensible. The concept has also gained much attention from a wide range of scientists who have taken up the challenge of defining the boundaries and safe operating spaces, along with the consequences of not doing so (e.g., Steffen et al. 2015, Richardson et al. 2023, Planetary Boundaries Science 2025 inter alia).

The different boundaries

Rockstrom et al. (2009) defined 10 boundaries of which three were crossed (climate change, rate of biodiversity loss, nitrogen cycle) and two could not yet be determined (atmospheric aerosol loading and chemical pollution). Next, Steffen et al. (2015) assessed seven boundaries of which four were crossed (adding land system change). By 2023, Richardson et al. (2023) concluded that six of nine boundaries have been crossed (adding pollution or novel entities, and freshwater change). Recently, the PB concept has been expanded to consider ‘safe’ and “just” Earth system boundaries (ESBs). “Safe” ESBs are roughly equivalent to PBs for their focus on the Earth’s biophysical systems through an aggregation of regional conditions. “Just’ ESBs express limits for avoiding significant harm to current and future generations, notably human populations (Rockstrom et al. 2021, Gupta et al. 2023). Gupta et al. (2024), in their comprehensive analysis, concluded that seven of the eight ESB have been transgressed with the eighth, air pollution, being transgressed at many local levels globally.

The boundary for novel entities

It has been challenging to determine one or more PBs or ESBs for chemical pollution, which was re-defined as ‘novel entities’ by Steffen et al. (2015) to include other novel forms such modified life-forms. Much of this challenge comes from the enormous diversity of the novel entities’ domain. For example, Wang et al. (2020) estimated that 350,000 chemicals have been registered for use globally of which 50,000 are considered confidential and 70,000 have ambiguous descriptions and thus are outside of easy assessment. Various attempts have been made to define or at least comment on this boundary (e.g., Persson et al. 2013, MacLeod et al. 2014, Diamond et al. 2015). Recently Persson et al. (2022) took up the challenge, concluding that the PB for novel entities has been crossed because the annual production and releases of chemical pollutants far outpaces the global capacity of assessment, let alone control.

Scientific efforts to “take the temperature” of the Earth’s biophysical systems continue by assessing their state with respect to PBs, with human justice now included in the assessment (e.g., Planetary Boundaries Science 2025). In terms of impact, the concept continues to reach the public, policy-makers and scientists; some national to international bodies are using the concept to advance environmentally protective policies. Let’s all hope that all these efforts will pull us back from transgressing PBs, for the sake of us and future generations.

Recorded Lecture

Miriam Diamond, who is an environmental chemist and Professor at the University of Toronto, described the earth system boundary framework and how chemicals are contributing to the transgression of the earth system boundary for novel entities.

Key Reading

Rockström, J. et al. 2009. A safe operating space for humanity. Nature 461, 472-475. https://doi.org/10.1038/461472a
Rockström, J. et al. 2023. Safe and just Earth system boundaries. Nature 619: 102-111. https://doi.org/10.1038/s41586-023-06083-8
Gupta J. et al. 2024. A just world on a safe planet: a Lancet Planetary Health-Earth Commission report on Earth-system boundaries, translations, and transformation. Lancet Planetary Health 8: E813-E873. https://doi.org/10.1016/S2542-5196(24)00042-1
Diamond M. et al. 2015. 2015. Exploring the planetary boundary for chemical pollution. Environment International 78:8-15. https://doi.org/10.1016/j.envint.2015.02.001
Persson L. et al. 2022. Outside the safe operating space of the planetary boundary for novel entities. Environ Sci Technol 56: 1510-1521. https://doi.org/10.1021/acs.est.1c04158