Planetary Boundaries

Scientists have pinpointed nine ‘Planetary Boundaries’ that mark the limits for our life support system. Within these limits, there is a safe operating space for life as we know it today. Crossing them threatens planetary health and therefore our own health. Knowing what they are helps us to address the challenges, develop new policies and plan for the future.

We have crossed four boundaries already, with some fast approaching their thresholds:

1. Climate change: Burning fossil fuels and cutting down forests has increased carbon dioxide levels in the atmosphere, warming the planet, melting the ice, raising the sea and changing the weather.
   Boundary: Atmospheric CO₂ levels no higher than 350 parts per million (ppm)
   Pre-industrial level: 280 ppm
   Current level: 414 ppm
   Diagnosis: Boundary exceeded
2. Biodiversity loss: A reduction in the number of plant and animal species and health of ecosystems.
   Boundary: Annual species extinction rate no more than 10 per million per year
   Current level: At least 100 per million per year
   Diagnosis: Boundary far exceeded
3. Ozone depletion: Chemicals used in refrigeration systems and deodorant sprays released pollutants that created a hole in the atmospheric ozone layer that filters out dangerous UV light.
   Boundary: Average stratospheric ozone > 276 Dobson units
   Current level: 283 Dobson units
   Diagnosis: Safe, and improving
4. Ocean acidification: More carbon dioxide in the atmosphere means that more is absorbed by the oceans, creating carbonic acid. This lowers the amount of calcium carbonate in the oceans (calcite and aragonite) needed by marine life to make shells and coral.
   Boundary: >80% of pre-industrial aragonite saturation in ocean water
   Pre-industrial level: 3.44:1
   Current level: 84% (2.90:1)
   Diagnosis: Safe for now, but some oceans will cross the threshold by mid-century
5. Freshwater use: A quarter of the world’s river systems no longer reach the ocean for at least part of the year resulting in droughts, damaged habitats and poor fisheries. A human populations rise, water demand rises and our impact on rivers, lakes and dams rises.
   Boundary: No more than 4000 km³ of fresh water consumed per year
   Current level: 2600 km³ per year
   Diagnosis: Boundary will be approached by mid-century
6. Land-system change: Forests, grasslands and other habitats have been converted to agricultural land to produce food and fuel, impacting ecosystems and their interactions.
   Global Boundary: 75% of pre-industrial forest cover
   Regional Boundary: Tropical – 85% / Temperate – 50% / Boreal – 85%
   Current Global average: 62%
   Diagnosis: Boundary exceeded
7. Biogeochemical flows (nutrient cycles): Phosphate and nitrogen cycles (which provide essential nutrients for life) have been disrupted due to their use in fertilisers. More of each is entering soils and then running into freshwater and oceans leading to algal blooms and suffocation/stagnation of environments.
   Phosphorus Boundary: 11 Tg P/yr ^-1
   Current level: 22 Tg P/yr ^-1
   Nitrogen Boundary: 62 Tg N/yr^-1
   Current level: 150 Tg N/yr^-1
   Diagnosis: Both boundaries far exceeded
8. Atmospheric aerosols: air pollution affects; the amount of solar radiation we receive, the formation of clouds (rain and snow) and human health.
   Boundary: Not yet identified
9. New materials and pollution: synthetic materials, heavy metals and radioactivity created from human activities are accumulating in the food chain, affecting fertility and the health of many species, including our own.
   Boundary: Not yet identified

^{This Planetary Boundaries Framework image is a taken from Deep Time Cards (Card: “Stabilised or Hothouse Earth?”). Copyright Deep Time Walk and Stockholm Resilience Centre.}