Rockstrom and others (Rockstrom et al., 2009, p. 472) proposed the use of planetary boundaries as a metric for measuring and, more importantly, mitigating human-made damage to the planet. They presented a novel approach (for the year 2009) to defining preconditions for human development, emphasizing the significance of respecting biophysical thresholds. The authors argue that three out of nine planetary boundaries have already been exceeded.

It is essential to acknowledge that before the Anthropocene, environmental changes occurred naturally, although human impact on the environment has always existed. In modern times, human actions, particularly the use of fossil fuels and industrialized agriculture, are the primary drivers of global environmental change. The proposed approach by Rockstrom et al. (2009), utilizing boundaries, aims to define "the safe operating space for humanity with respect to the Earth system and is associated with the planet's biophysical subsystems or processes" (p. 472). Processes requiring defined planetary boundaries include climate change, biodiversity loss, and others, often based on critical values such as carbon dioxide concentration (p. 472).
In 2015, the same group of researchers (Steffen et al., 2015) further developed the concept of Planetary Boundaries. Although maintaining the core idea quite strictly, the updated framework places emphasis on climate change and biodiversity loss, now termed biosphere integrity, as the central processes of the entire Earth system. These processes, interlinked with others, have the most significant impact on the Earth system, leading to irreversible changes. If crossing other boundaries would unavoidably leave serious consequences, climate change and biosphere integrity are like pillars, which sustain all the life on Earth and are linked to irreversible changes.

In Rockstrom et al. (2009, p. 475), it is mentioned that the research has tentatively quantified seven (out of nine) boundaries, but gaps in information still persist, therefore other aspects are mostly “scientific guesses”. New insights, as indicated by Steffen and colleagues (2015, p. 736), have closed some of these gaps, but the complexity of the Earth system makes it challenging to present "the full picture." They further stress that additional data is needed. For example, “At present, only one regional boundary (south Asian monsoon) can be established for atmospheric aerosol loading.” (p. 736). Thus, additional data is deemed necessary, such as establishing regional boundaries for atmospheric aerosol loading. Exceeded boundaries include climate change, biodiversity loss, and the nitrogen cycle, with evidence based on observed changes in global temperature, species extinction rates, and nitrogen levels in the environment. Evidence for these exceedances may involve observed changes in global temperature, species extinction rates, and nitrogen levels in the environment. For example, a measurement of climate change would be parts per million (ppm) of carbon dioxide (safe limit – 350, current – around 400). Recent discoveries, the research by Persson and colleagues (2022), even further stress boundary exceeding, specifically for pollutants.

Surprisingly, Rockstrom et al. (2009) and Steffen et al. (2015) predominantly measure impact from a human well-being perspective, focusing solely on human safety and a safe environment for them (appears that - mostly). Rockstrom and others (2009, p. 472) (Steffen et al., 2015, p. 7, put it under novel entities) despite having a boundary for chemical pollution, they exclude other types of pollution like noise, light, or thermal pollution. Notably, neither study mentions a Planetary boundary for human population (i.e., overpopulation), possibly reflecting an anthropocentric focus. The absence of such boundaries could exacerbate the overall human-created impact on the environment, even with improvements in other sustainability measures, given the interconnectedness of Earth's systems. For example, we can keep usage of unsustainable resources low, but how will we adapt this change to the still growing human population and their needs? Are we ready for even bigger population with the resources available without exceeding boundaries?

Examining the proposed Planetary Boundaries, both in the original and updated versions, reveals advantages and disadvantages from a pedagogical perspective. On one hand, boundaries offer a simple way to convey that human impact cannot be limitless, requiring implementation of specific restrictions. They set clear limits and elucidate potential consequences. On the other hand, the Planetary Boundaries framework may appear overly simplistic, potentially making complex issues seem deceptively simple and manageable, overlooking feedback loops. Moreover, it might convey that unsustainable resource use and practices are acceptable until the limits are reached. A notable drawback is the reductionist nature of the framework, lacking clear connections between boundaries and dimensions, thereby risking oversimplification.

Considering the aforementioned, incorporating the Planetary Boundaries as a framework in an educational curriculum requires clear explanations to avoid oversimplification. Quoting Steffen and others (2015): "The PB framework does not dictate how societies should develop. These are political decisions that must include consideration of the human dimensions, including equity, not incorporated in the PB framework" (p. 736). Students need to understand that the boundaries measure the direction and sustainability of human impact but are not a comprehensive tool for policy changes or an explanation of Earth processes. Precision in these observations is challenging, and the boundaries should be viewed as indicators of impact rather than absolute guidelines.

List of references:
Persson, L., Carney Almroth, B., M., Collins, C., D., Cornell, S., De Wit, C., A., Diamond, M., L., Fantke, P., Hassellöv, M., MacLeod, M., Ryberg, M., W., Søgaard Jørgensen, P., Villarrubia-Gómez, P., Wang, Z., Zwicky Hauschild, M. (2022). Outside the Safe Operating Space of the Planetary Boundary for Novel Entities. Environmental Science & Technology, 56 (3), 1510-1521. DOI: 10.1021/acs.est.1c04158

Rockström, J., Steffen, W., Noone, K., Persson, Å., Chapin III, F. S., Lambin, E. F., Lenton, T. M., Scheffer, M., Folke, C., Schellnhuber, H. J., Nykvist, B., de Wit, C. A., Hughes, T., van der Leeuw, S., Rodhe, H., Sörlin, S., Snyder, P. K., Costanza, R., Svedin, U., Falkenmark, M., Karlberg, L., Corell, R. W., Fabry, V. J., Hansen, J., Walker, B., Liverman, D., Richardson, K., Crutzen, P., Foley, J. A. (2009). A safe operating space for humanity. Nature 461, 472–475. Available at https://doi-org.ezproxy.ub.gu.se/10.1038/461472a

Steffen, W., Richardson, K., Rockström, J., Cornell, S. E., Fetzer, I., Bennett, E. M., Biggs, R., Carpenter, S. R., de Vries, W., de Wit, C. A., Folke, C., Gerten, D., Heinke, J., Mace, G. M., Persson, L. M., Ramanathan, V., Reyers, B., Sörlin, S. (2015). Planetary boundaries: Guiding human development on a changing planet. Science 347, 1259855. DOI: 10.1126/science.1259855