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Scientists note nine planetary boundaries beyond which we can’t push Earth Systems without putting our own societies at risk:
1. climate change,
2. biodiversity loss,
3. ocean acidification,
4. ozone depletion,
5. atmospheric aerosol pollution,
6. freshwater use,
7. biogeochemical flows of nitrogen and phosphorus,
8. system change, and
9. release of novel chemicals.
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All life on Earth, and human civilization, are sustained by vital biogeochemical systems, which are in delicate balance. However, our species — due largely to rapid population growth and explosive consumption — is destabilizing these Earth processes, endangering the stability of the “safe operating space for humanity.”
Scientists note nine planetary boundaries beyond which we can’t push Earth Systems without putting our societies at risk: climate change, biodiversity loss, ocean acidification, ozone depletion, atmospheric aerosol pollution, freshwater use, biogeochemical flows of nitrogen and phosphorus, land-system change, and release of novel chemicals.
Humanity is already existing outside the safe operating space for at least four of the nine boundaries: climate change, biodiversity, land-system change, and biogeochemical flows (nitrogen and phosphorus imbalance). The best way to prevent overshoot, researchers say, is to revamp our energy and food systems.
In 2021, three meetings offer chances to avoid planetary boundary overshoot: the Convention on Biological Diversity meeting in Kunming, China; the U.N. Climate Summit (COP26) in Glasgow, U.K.; and the U.N. Food Systems Summit in Rome. Agreements with measurable, implementable, verifiable, timely and binding targets are vital, say advocates.
Advanced human societies emerged during an unprecedented period of stability on Earth. During the 12,000 years prior to the Industrial Revolution, our planet’s surface temperature varied by less than 1° Celsius (1.8° Fahrenheit) above or below the average for that entire period. As a result, life — both human and wild — thrived.
But over the past two centuries, humanity has dramatically increased greenhouse gas concentrations in the atmosphere, pushing us outside this “safe” climate zone; outside the conditions for which civilization has been designed.
Unfortunately for us, climate change represents just one of nine critical planetary boundaries, which the imprudent actions of our species risk dangerously destabilizing and overshooting.
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However, our species — due largely to rapid population growth and explosive consumption — is destabilizing these Earth processes, endangering the stability of the “safe operating space for humanity.”
Scientists note nine planetary boundaries beyond which we can’t push Earth Systems without putting our own societies at risk:
1. climate change,
2. biodiversity loss,
3. ocean acidification,
4. ozone depletion,
5. atmospheric aerosol pollution,
6. freshwater use,
7. biogeochemical flows of nitrogen and phosphorus,
8. system change, and
9. release of novel chemicals.
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All life on Earth, and human civilization, are sustained by vital biogeochemical systems, which are in delicate balance. However, our species — due largely to rapid population growth and explosive consumption — is destabilizing these Earth processes, endangering the stability of the “safe operating space for humanity.”
Scientists note nine planetary boundaries beyond which we can’t push Earth Systems without putting our societies at risk: climate change, biodiversity loss, ocean acidification, ozone depletion, atmospheric aerosol pollution, freshwater use, biogeochemical flows of nitrogen and phosphorus, land-system change, and release of novel chemicals.
Humanity is already existing outside the safe operating space for at least four of the nine boundaries: climate change, biodiversity, land-system change, and biogeochemical flows (nitrogen and phosphorus imbalance). The best way to prevent overshoot, researchers say, is to revamp our energy and food systems.
The Nine Planetary Boundaries: A closer look
The Planetary Boundaries Framework (last updated in 2015) defines nine key Earth System processes and sets safe boundaries for human activities. They are:
Climate change: Rising concentrations of greenhouse gases in the atmosphere are leading to increasing global temperatures. We passed the safe boundary of 350 parts per million of CO2 in 1988. By 2020, levels were 417ppm.
Novel entities: One of the more elusive planetary boundaries, novel entities refers to harmful chemicals, materials, and other new substances (such as plastics), as well as naturally-occurring substances such as heavy metals and radioactive materials released by human activities. We release tens of thousands of synthetic substances into the environment every day, often with unknown effects. These risks are exemplified by the danger posed by CFCs to the ozone layer, or of DDT to biodiversity.
Stratospheric ozone depletion: The depletion of O3 in the stratosphere as a result of chemical pollutants was first discovered in the 1980s and led to the 1987 Montreal Protocol on Substances that Deplete the Ozone Layer. The ozone layer is now showing signs of recovery.
Atmospheric aerosols: Atmospheric aerosol pollution is a bane to human health and can also influence air and ocean circulation systems that affect the climate. For example, severe aerosol pollution over the Indian subcontinent may cause the monsoon system to abruptly switch to a drier state.
Ocean acidification: Rising atmospheric CO2 levels are increasing the acidity of the world’s oceans, posing a severe risk to marine biodiversity and particularly invertebrates whose shells dissolve in acidic waters.
Biogeochemical flows: We have profoundly altered the planet’s natural nitrogen and phosphorus cycles by applying these vital nutrients in large quantities to agricultural land, leading to runoff into neighboring ecosystems.
Freshwater use: Agriculture, industry and a growing global population are putting ever greater strain on the freshwater cycle, while climate change is altering weather patterns, causing drought in some regions and flooding in others.
Land-system change: Changes in land-use, particularly the conversion of tropical forests to farmland, have a major effect on climate because of the impact on atmospheric carbon dioxide concentrations, on biodiversity, freshwater, and the reflectivity of the Earth’s surface.
Biosphere Integrity: The functional integrity of ecosystems is a core planetary boundary because of the many ecoservices they provide, from pollination to clean air and water. Scientists are concerned about rapid declines in plant and animal populations, the degradation of ecosystems, and the loss of genetic diversity which could disrupt essential biosphere services.
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The nine boundaries humanity must respect to keep the planet habitable
Image and explanations courtesy of J. Lokrantz/Azote based on Steffen et al. (2015) via Stockholm Resilience Centre.
