Definition
Planetary boundary
A planetary boundary is a threshold beyond which human activities risk causing catastrophic environmental change.
- The planetary boundaries model, developed by Johan Rockström and colleagues, defines nine critical Earth system processes that regulate the planet’s stability.
- Each boundary represents a safe operating limit within which humanity can continue to thrive without causing irreversible environmental change.
- Crossing these boundaries increases the risk of tipping points that can destabilize global systems.
- One of these nine boundaries is biosphere integrity, which focuses on the health, diversity, and functioning of ecosystems and species that sustain life on Earth.
As of 2023, six of the nine boundaries have been transgressed, including biosphere integrity, signaling that humanity is operating outside the Earth’s safe limits.
Understanding Biosphere Integrity
- Biosphere integrity reflects how intact and functional Earth’s biological systems are.
- It encompasses both:
- Genetic diversity: variation within and between species that enables adaptation.
- Functional diversity: the roles species play (e.g., pollination, decomposition, nutrient cycling).
Interrelationship Between Ecosystems and Species Diversity
- Ecosystem health and species diversity are mutually dependent:
- Diverse species ensure resilience, enabling ecosystems to recover from disturbances.
- Stable ecosystems provide habitats and resources that sustain species populations.
- When biodiversity declines, ecosystems lose resilience, leading to ecosystem collapse and further biodiversity loss in a positive feedback loop.
When biodiversity declines, ecosystems lose stability and resilience, making them more vulnerable to disturbances like climate change, pollution, and habitat destruction.
Human Activities and Loss of Biosphere Integrity
- Habitat destruction and fragmentation (deforestation, urbanization).
- Pollution (air, water, and soil contamination).
- Climate change altering temperature, rainfall, and habitats.
- Invasive species displacing native biodiversity.
- Overexploitation of resources (overfishing, hunting, mining).
Overfishing has led to population crashes in species like cod and tuna, disrupting entire marine food webs.
Evidence for Crossing the Biosphere Integrity Boundary
Extinction Rates
- The background extinction rate (natural rate) is 0.1–1 E/MSY (extinction per million species-years).
- The current human-induced rate is estimated at 100–1000 E/MSY, meaning extinctions are occurring 100 to 1000 times faster than natural rates.
- This level indicates the biosphere integrity boundary has been transgressed.
- The unit E/MSY expresses the number of species that go extinct per million species per year.
- Crossing 10 E/MSY signifies leaving the safe operating space.
- Since 1500, the IUCN Red List has documented over 900 extinctions.
- These include 86% animals and 14% plants, mainly due to human-induced pressures.
- Extinctions are concentrated in Pacific islands, the Americas, and tropical Africa.
Biodiversity Intactness Index (BII)
- BII measures the average abundance of native species compared to an undisturbed ecosystem.
- A BII ≥ 90% = within safe boundary (ecosystem resilient).
- A BII between 30–90% = reduced resilience and ecosystem degradation.
- A BII ≤ 30% = ecosystem collapse risk.
- Global BII averages below 90%
- Large parts of South America, Sub-Saharan Africa, and Southeast Asia have BIIs below 60%, indicating that biosphere integrity has fallen below safe thresholds globally.
Why Reversal is Urgent
- The biosphere supports all life and underpins every other planetary boundary (e.g., climate regulation, nutrient cycling, freshwater stability).
