Why does the Earth have boundaries?

Many anthropogenic drivers, from CO₂ emissions over land appropriation to freshwater pollution, are driving the Earth system ever faster towards tipping points.^1,2 Crossing tipping points has potentially devastating consequences³ for our society. Examples of such tipping elements in the Earth system are the Amazon rainforest or the polar ice sheets.

The concept of planetary boundaries^4-6 was developed to make tipping risks more tangible. It comprises nine essential Earth systems: climate, biodiversity, freshwater, land use, biogeochemical cycles, ozone, ocean acidification, aerosols, and novel entities. If the impacts on all of these categories remain below the defined thresholds, the Earth system remains in the stable state that we know with certainty to be preferable and supportive for human societies. In contrast, transgressing these boundaries leads to increased risks of the Earth system transitioning to a different state that is no longer supportive for human civilization.⁷

How can tipping risks be reduced?

Through a fast defossilization of the energy system,^8,9 replacing coal, oil and gas with renewable energy,¹⁰ transforming agriculture,¹¹ and establishing a sustainable circular economy.¹² Since the production of resources and technologies for the transformation also causes significant environmental impacts at planetary boundaries,¹³ all measures that reduce the need for resources help to minimize tipping risks. For example, if we align our energy demand with the availability of solar and wind—the paradigm of the sunflower society¹⁴—much less energy storage capacity would be required, which in turn would save significant amounts of materials, energy, time, and money.

The circular economy follows the same logic: rethink, reuse, reshape, renovate, adapt, recycle what already exists. Just as nature functions in almost perfectly closed cycles, circular economy aims to reduce resource consumption and the associated environmental impacts as much as possible.^15-17

And finally: cleaning up!

Atmospheric CO₂ concentration is already well above the save limit of 350ppm, requiring us to clean-up a part of the emissions we have released into the atmosphere since the industrial revolution.^18-21

Cleaning up past pollution and repairing its damage is also necessary for other severely deteriorated Earth systems, such as restoring habitats²² or ridding the oceans from plastic pollution.²³

References

1. Lenton, T. M. et al. The Global Tipping Points Report 2023. (University of Exeter, Exeter, UK, 2023).
2. Wunderling, N. et al. Global warming overshoots increase risks of climate tipping cascades in a network model. Nature Climate Change 13, 75-82 (2022). https://doi.org:10.1038/s41558-022-01545-9 
3. Kemp, L. et al. Climate Endgame: Exploring catastrophic climate change scenarios. Proc Natl Acad Sci U S A 119, e2108146119 (2022). https://doi.org:10.1073/pnas.2108146119 
4. Rockström, J. et al. Planetary Boundaries: Exploring the Safe Operating Space for Humanity. Ecology and Society 14, 1-33 (2009).
5. Steffen, W. et al. Sustainability. Planetary boundaries: guiding human development on a changing planet. Science 347, 1259855 (2015). https://doi.org:10.1126/science.1259855 
6. Richardson, K. et al. Earth beyond six of nine planetary boundaries. Sci Adv 9, eadh2458 (2023). https://doi.org:10.1126/sciadv.adh2458
7. Steffen, W. et al. Trajectories of the Earth System in the Anthropocene. Proc Natl Acad Sci U S A 115, 8252-8259 (2018). https://doi.org:10.1073/pnas.1810141115 
8. Desing, H. & Widmer, R. Reducing climate risks with fast and complete energy transitions: applying the precautionary principle to the Paris agreement. Environmental Research Letters 16, 121002 (2021). https://doi.org:10.1088/1748-9326/ac36f9 
9. United Nations Environment Programme. Emission Gap Report 2022: The Closing Window - Climate crisis calls for rapid transformation of societies. (UNEP, Nairobi, 2022).
10. Desing, H., Widmer, R., Beloin-Saint-Pierre, D., Hischier, R. & Wäger, P. Powering a Sustainable and Circular Economy—An Engineering Approach to Estimating Renewable Energy Potentials within Earth System Boundaries. Energies 12, 1-18 (2019). https://doi.org:10.3390/en12244723 
11. Gerten, D. et al. Feeding ten billion people is possible within four terrestrial planetary boundaries. Nature Sustainability (2020). https://doi.org:10.1038/s41893-019-0465-1 
12. Desing, H. et al. A circular economy within the planetary boundaries: Towards a resource-based, systemic approach. Resources, Conservation and Recycling 155 (2020). https://doi.org:10.1016/j.resconrec.2019.104673 
13. UNEP. Global Resources Outlook 2024: Bend the Trend – Pathways to a liveable planet as resource use spikes. (International Resource Panel, Nairobi, 2024).
14. Desing, H. & Widmer, R. How Much Energy Storage can We Afford? On the Need for a Sunflower Society, Aligning Demand with Renewable Supply. Biophysical Economics and Sustainability 7, 3 (2022). https://doi.org:10.1007/s41247-022-00097-y 
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16. Haupt, M. & Hellweg, S. Measuring the environmental sustainability of a circular economy. Environmental and Sustainability Indicators 1-2 (2019). https://doi.org:10.1016/j.indic.2019.100005 
17. Hummen, T. & Desing, H. When to replace products with which (circular) strategy? An optimization approach and lifespan indicator. Resources, Conservation and Recycling 174 (2021). https://doi.org:10.1016/j.resconrec.2021.105704 
18. Desing, H., Gerber, A., Hischier, R., Wäger, P. & Widmer, R. The 3‐Machines Energy Transition Model: Exploring the Energy Frontiers for Restoring a Habitable Climate. Earth's Future 10, 1-15 (2022). https://doi.org:10.1029/2022ef002875 
19. Desing, H. Below zero. Environmental Science: Advances, 612-619 (2022). https://doi.org:10.1039/d2va00168c 
20. Churkina, G. et al. Buildings as a global carbon sink. Nature Sustainability (2020). https://doi.org:10.1038/s41893-019-0462-4 
21. Lura, P. et al. Mining the Atmosphere: A Concrete Solution to Global Warming. Resources, Conservation and Recycling (submitted). https://doi.org:10.2139/ssrn.4769672 
22. IPBES. The IPBES assessment report on land degradation and restoration., (Secretariat of the Intergovernmental Science-Policy Platform on Biodiversity and Ecosystem Services, 2018).
23. Richon, C., Kvale, K., Lebreton, L. & Egger, M. Legacy oceanic plastic pollution must be addressed to mitigate possible long-term ecological impacts. Microplastics and Nanoplastics 3 (2023). https://doi.org:10.1186/s43591-023-00074-2