TL;DR

The planetary boundaries are nine areas that represent a “safe operating space” for humanity. We have crossed six of them. This page offers a basic breakdown of each boundary to help those not trained in earth science understand what they mean.

• TL;DR
• What are the planetary boundaries?
• Boundaries we have passed
• Climate change
• Radiative forcing
• CO2 concentration
• Biosphere integrity
• Genetic diversity
• Planetary function
• Land system change
• Freshwater change
• Blue water
• Green water
• Biogeochemical flows
• Phosphorous (P)
• Nitrogen (N)
• Novel entities
• Boundaries at immediate risk
• Ocean acidification (WIP)
• Boundaries in the safe zone
• Atmospheric aerosol loading
• Stratospheric ozone depletion
• Resources

What are the planetary boundaries?

The physical status of the Earth since the last ice age has allowed human beings to flourish. Because the average global temperature was relatively stable for those 10,000 years, we were able to begin to settle down and grow our food rather than moving from place to place to hunt and gather it. It was this ability to settle that encouraged the growth of knowledge, ideas, and technology. However, once we figured out how to extract and burn fossil fuels and industrialize agriculture, humans became a major driving force of change on our planet.

In 2009, a group of 29 scientists came together to propose that nine key areas ensure a safe operating space on Earth—the planetary boundaries. The idea behind the boundaries was to look at the safe and stable Earth systems that had existed for the last 10,000 years but were now being thrown out of equilibrium by human activities.

The scientists from that 2009 paper argued that humanity was risking irreversible and catastrophic changes if we continued down our current path and that we had already crossed the boundary for three of those systems. Today, all nine of the boundaries have been quantified and analyzed, and we have now passed six of them.

• 2009: Planetary Boundaries: Exploring the Safe Operating Space for Humanity
• 2015: Planetary boundaries: Guiding human development on a changing planet
• 2023: Earth beyond six of nine planetary boundaries

Boundaries we have passed

Climate change

Radiative forcing

• Boundary: +1 watts per square meter (W/m2)
• Where we are: +2.91 W/m2

CO2 concentration

• Boundary: 350 parts per million carbon dioxide (ppm CO2)
• Where we are: 418 ppm CO2 (as of Sep 15, 2023)

Biosphere integrity

The biosphere is the area above and below the Earth’s surface that can sustain life. The biosphere doesn’t just refer to the living organisms, but also the material that feeds into sustaining that life.

Genetic diversity

• Boundary: <10 extinctions/million species-years
• Where we are: >100 extinctions/million species-years

Planetary function

• Boundary: 10% human appropriation of net primary productivity (HANPP)
• Where we are: 30% HANPP

Land system change

Source: CarbonBrief

Freshwater change

We can’t afford to waste fresh water. Of all the water on Earth, less than 3% is fresh, and most of that (about 2.5%) isn’t accessible to us—it’s locked up in ice, too polluted, or too far underground to extract affordably.

The previous planetary boundaries assessments only looked at water consumption as a measure of total freshwater change. Splitting this boundary into two components was done to give a better representation of the true extent and impacts on the water cycle, and to allow more consistent comparisons over time.

Blue water

Blue water = surface and groundwater.

• Boundary: 10.2% disturbance of blue water flow
• Where we are: 18.2% disturbance of blue water flow

Green water

Green water = water that is available to plants.

• Boundary: 11.1% human-induced disturbance of water available to plants
• Where we are: 15.8% human-induced disturbance of water available to plants

Biogeochemical flows

Phosphorous (P)

• Boundary:
• Global: 11 teragrams* (Tg) P flowing into the ocean/year
• Regional: 6.2 Tg P applied to soils/year
• Where we are:
• Global: 22.6 Tg P flowing into the ocean/year
• Regional: 17.5 P applied to soils/year

P was originally set as a global boundary, but the regional component was added because freshwater systems are so sensitive to too much of this nutrient, and this effect is very regional.

Nitrogen (N)

• Boundary: 62 Tg N applied to soil/year
• Where we are: 190 Tg N applied to soil//year

*A teragram is one trillion grams. One teragram = one million tonnes.

Novel entities

• Boundary: 0% of untested synthetic material
• Where we are: unknown, but definitely higher than 0%

Boundaries at immediate risk

Ocean acidification (WIP)

• Boundary: 3.44 the average global surface ocean saturation state with respect to aragonite (Ωarag)
• Where we are: 2.8 Ωarag

Boundaries in the safe zone

Atmospheric aerosol loading

• Boundary: 0.1 mean annual interhemispheric difference
• Where we are: 0.076 mean annual interhemispheric difference

Stratospheric ozone depletion

• Boundary: 276 Dobson units (DU)
• Where we are: 284.6 DU

We published this Notion because the planetary boundaries influence our approach to investing, and we want other people to understand what they mean for our lives and our planet. Investing in climate means so much more than just tons of CO2. All of these boundaries are interconnected, and we can’t address one without the others.

Resources

• Planetary boundaries (Stockholm Resilience Center)
• Radiative Forcing (MIT Climate Portal)
• Global water cycle shifts far beyond pre-industrial conditions – planetary boundary for freshwater change transgressed [pre-print] (Porkka et al., 2023)
• Earth beyond six of nine planetary boundaries (Richardson et al., 2023)
• Sensitivity of tropical monsoon precipitation to the latitude of stratospheric aerosol injections (Krishnamohan & Bala, 2022)
• Outside the Safe Operating Space of the Planetary Boundary for Novel Entities (Persson et al., 2022)
• A planetary boundary for green water (Wang-Erlandsson et al., 2022)
• [VIDEO] Evidence for human generated increases in atmospheric carbon dioxide (Crash Chemistry Academy, Jul 2022)
• Safe planetary boundary for pollutants, including plastics, exceeded, say researchers (SEI, Jan 2022)
• Climate Response to Latitudinal and Altitudinal Distribution of Stratospheric Sulfate Aerosols (Zhao et al., 2021)
• Rebuilding the ozone layer: how the world came together for the ultimate repair job (UNEP, Sep 2021)
• Changes to Carbon Isotopes in Atmospheric CO2 Over the Industrial Era and Into the Future (Graven et al., 2020)
• Tracking fossil fuel emissions with carbon-14 (NOAA Research, Jun 2020)
• Planting non-native trees accelerates the release of carbon back into the atmosphere (The Conversation, Jun 2020)
• Climate Change Indicators: Climate Forcing (EPA, Nov 2020)
• Restoring natural forests is the best way to remove atmospheric carbon (Lewis et al., 2019)
• Accelerated modern human–induced species losses: Entering the sixth mass extinction (Ceballos et al., 2015)
• The effectiveness of coral reefs for coastal hazard risk reduction and adaptation (Ferrario et al., 2014)
• Management of nitrogen fertilizer to reduce N2O emissions from field crops (Michigan State University, Nov 2014)
• Reconsideration of the planetary boundary for phosphorus (Carpenter & Bennett, 2011)
• A safe operating space for humanity (Rockström et al., 2009)

Thank you to Meighan Boyd, PhD and Joseph Timkovsky, PhD for reviewing this text prior to publishing.

Last updated: Sep 2023