Context: A new study co-authored by a climate scientist Johan Rockstrom said that Earth is exceeding its safe operating space for humanity in six of nine key measurements of its health, and two of the remaining three are headed in the wrong direction.
The Study on Planetary Boundaries
The study evaluates the health of the Earth using nine key measurements or boundaries that are critical for the well-being of humanity and the planet.
- It proposes a new approach to global sustainability by defining planetary boundaries within which humanity can operate safely.
- Transgressing one or more planetary boundaries may be deleterious or even catastrophic due to the risk of crossing thresholds that will trigger non-linear, abrupt environmental change within continental- to planetary-scale systems.
Nine Planetary Boundaries
The study identified nine planetary boundaries and, drawing upon current scientific understanding, it proposes quantifications for seven of them.
| Earth System Process | Limit | Implication of Crossing the limit |
| Climate Change | CO2 concentration in the atmosphere <350 ppm and/or a maximum change of +1 W m-2 in radiative forcing | Loss of polar ice sheets. Regional climate disruptions. Loss of glacial freshwater supplies.Weakening of carbon sinks. |
| Ocean Acidification | Mean surface seawater saturation state with respect to aragonite ≥ 80% of pre-industrial levels | Conversion of coral reefs to algal-dominated systems. Regional elimination of some aragonite- and high- magnesium calcite-forming marine biota.Slow variable affecting marine carbon sink. |
| Stratospheric Ozone Depletion | <5% reduction in O3 concentration from pre-industrial level of 290 Dobson Units | Severe and irreversible UV- B radiation affects human health and ecosystems. |
| Biogeo-Chemical Flows: interference with P and N cycles | Limit industrial and agricultural fixation of N2 to 35 Tg N yr-1 Annual P inflow to oceans not to exceed 10 times the natural background weathering of P | P: avoid a major oceanic anoxic event (including regional), with impacts on marine ecosystems. N: slow variable affecting overall resilience of ecosystems via acidification of terrestrial ecosystems and eutrophication of coastal and freshwater systems. |
| Global Freshwater Use | <4000 km3 yr-1 of consumptive use of runoff resources | Could affect regional climate patterns (e.g., monsoon behavior).Primarily slow variable affecting moisture feedback, biomass production, carbon uptake by terrestrial systems and reducing biodiversity |
| Land System Change | <15% of the ice-free land surface under cropland | Trigger of irreversible and widespread conversion of biomes to undesired states.Primarily acts as a slow variable affecting carbon storage and resilience via changes in biodiversity and landscape heterogeneity |
| Rate of Biodiversity Loss | Annual rate of <10 extinctions per million species | Slow variable affecting ecosystem functioning at continental and ocean basin scales.Impact on many other boundaries—C storage, freshwater, N and P cycles, land systems.Massive loss of biodiversity unacceptable for ethical reasons. |
| Chemical Pollution | To be determined | Thresholds leading to unacceptable impacts on human health and ecosystem functioning possible but largely unknown.May act as a slow variable undermining resilience and increase risk of crossing other thresholds |
| Atmospheric Aerosol Loading | To be determined | Disruption of monsoon systems. Human-health effects. Interacts with climate change and freshwater boundaries. |
Properties of Proposed Planetary Boundaries
- Planetary boundaries are interdependent, because transgressing one may both shift the position of other boundaries or cause them to be transgressed.
- The social impacts of transgressing boundaries will be a function of the social–ecological resilience of the affected societies.
- The proposed concept of “planetary boundaries” aimed at minimizing negative externalities, toward the estimation of the safe space for human development.
- Planetary boundaries define, as it were, the boundaries of the “planetary playing field” for humanity if we want to be sure of avoiding major human-induced environmental change on a global scale.
New Findings on the Planetary Boundaries
- Unsafe in Six Areas: According to the study, Earth is exceeding its “safe operating space for humanity” in six out of these nine measurements.
- These areas include climate, biodiversity, land use, freshwater resources, nutrient pollution, and the presence of “novel” chemicals (human-made compounds like microplastics and nuclear waste).
- Safe in Three Areas (for now): Only three of the nine measurements are currently within the boundaries considered safe.
- These areas are the acidity of the oceans, the health of the air, and the state of the ozone layer.
- Negative Trends:
- The study also indicates that even in the areas considered “safe,” namely the oceans and air quality, there are negative trends.
- Ocean and air pollution are on the rise, which is a cause for concern.
- Updating the Boundaries:
- The study is an update from 2015 and introduced a new factor – water quality – to the list of unsafe measurements.
- This change was based on worsening river run-off and improved measurements and understanding of the issue.
- Global Significance:
- The researchers emphasize that these nine factors are critical determinants of the planet’s fate.
- Their findings underscore the urgent need for global action to address environmental and ecological challenges.
- Expert Consensus: The boundaries used in the study are described as “scientifically well established” and have been supported by various outside studies and research.
