1.2.7 Planetary boundaries

Helpful prior knowledge and learning objectives:

Helpful prior learning:



Learning objectives:

You might think that we have only recently started to understand the risks of climate change and other ecological damage. But more than 50 years ago, a group of scientists from MIT used computer models to research how population and economic growth were affecting Earth’s resources. They published their research in 1972 in a best-selling book called The Limits to Growth. 

The scientists concluded that if economic growth continued, even with slowing population growth and improved technologies, we could face a collapse of our economic and social systems within 100 years (from 1970) due to damage to Earth’s ecosystems. The scientists recommended significant changes to the economy to limit growth and protect Earth’s life-support systems.

Unfortunately many economists, business leaders and politicians dismissed the research. The scientists' conclusions and recommendations went against economic theories that assume that endless economic growth is possible and necessary. After huge initial interest in the Limits to Growth report, it was pushed aside as countries continued to blindly use energy and matter to grow their economies.

Recent research shows that many of the predictions of The Limits to Growth were correct, and new computer models are now being used to determine what we can still do to avoid the catastrophes predicted in the report. The models used in the MIT research and current research are enormously valuable, but only if we pay attention to what they tell us.

Cover of the original Limits to Growth report

Figure 1. Warnings about ecological crises from more than 50 years ago

(Credit: Amazon/Wikipedia)

What are planetary boundaries?

Since the 1970s, scientists have continued research to understand how much damage human economic activity is doing to Earth’s systems. Scientists have identified nine interconnected Earth systems that are critical to maintaining stable conditions for life on Earth.


With the help of new computer models, scientists have identified probable limits to human disturbance of each of Earth’s systems. If we cross these limits, some planetary systems may reach a tipping point (Section S.x) where conditions change very rapidly with widespread risks for life on Earth.


The planetary boundaries model illustrates these nine Earth systems and their limits (Figure 2). The “safe operating space” for human economic activity is the green area within the dotted line. Research shows that we have crossed the safe operating space in six of nine Earth systems, with ocean acidification rapidly approaching the boundary.

Planetary boundaries model

Figure 2. Planetary boundaries model

(Credit: Stockholm Resilience Centre CC BY-NC-ND 3.0)

Climate change

This boundary measures levels of global warming.

Current global warming is +1.2-1.5°C from the pre-industrial period.  The

main driver is greenhouse gas emissions from burning fossil fuels for energy.

Novel entities

(Chemical pollution)

Industries release hundreds of thousands of chemicals into the environment. Many chemicals are untested for ecosystem impacts, but can remain in ecosystems for very long periods causing irreversible damage to the way they function.

Stratospheric ozone depletion

Stratospheric ozone filters out harmful ultraviolet (UV) radiation from the sun. Man-made chemical emissions in the atmosphere have damaged the ozone layer. The Montreal Protocol, a global agreement, limited these damaging emissions, keeping us inside the planetary boundary.

Atmospheric aerosol loading

(air pollution)

Humans emit microparticles or aerosols, like soot from burning waste, into the atmosphere through industrial production and transportation. These particles are often toxic to plants and animals and affect cloud formation and rainfall patterns that disrupt ecosystems.

Ocean acidification

Carbon dioxide (CO2) dissolves in ocean water, forming carbonic acid that damages the exoskeletons of some animals and threatens corals and the habitats they provide for fish and other marine organisms.

Biogeochemical flows

(phosphorus and nitrogen)

Agriculture uses fertilisers with phosphorus and nitrogen that run off into rivers, lakes and oceans. They support excessive toxic algae growth that blocks light to other organisms, and depletes oxygen from water bodies when they die and decay.

Freshwater change

Excessive use of surface water (blue water) and groundwater (green water) for agriculture, industry and households depletes water stocks and flows, interfering with the water cycle which supports the transfer and transformation of energy and matter in ecosystems.

Land-use change

Humans convert land, such as forest and wetlands, for human uses such as agriculture, material extraction, and the built environment. Land conversion depletes soil carbon, destroys ecosystem habitats and harms the land’s ability to cycle water, nitrogen and phosphorus.

Biosphere integrity 

(biodiversity)

Biodiversity is critical for ecosystem function and resilience. We have lost about 69% of Earth’s species since 1970 due to land use, pollution, and climate change.

You may have noticed that the same human economic activities - farming, overconsumption and the related industrial production, urbanisation - are causing us to cross multiple planetary boundaries. This is because of the wide ecological impacts of human transfers and transformations of energy and matter to meet our needs and wants. The multiple planetary boundary crossings also occur because these Earth systems are deeply connected to one another. For example, climate change amplifies biodiversity loss as habitats change. Land use amplifies climate change due to loss of forests and soils that sequester and store carbon.

Johan Rockström, one of the original creators of the planetary boundary model, briefly explains the model in the short video below. He then focuses on climate change to explain the multiple, interconnected tipping points we face in Earth’s climate system.

Activity 1.2.7

Concept: Systems

Skills: Thinking skills (critical thinking)

Time: 30 minutes

Type: Individual or pairs, then group


Connecting planetary boundaries

All Earth systems are interconnected, so the good news is that when we tackle one problem, we are likely to have positive impacts on the others.

Planetary boundaries model

Figure 2. Planetary boundaries model

(Credit: Stockholm Resilience Centre CC BY-NC-ND 3.0)

Now, consider Figure 4. This illustration conveys an important message about so-called ‘carbon tunnel-vision’. What is the message of this illustration? 


Discuss in your group, or with the entire class.

Illustration of carbon tunnel vision

Figure 3. Carbon tunnel-vision

(Credit: Deivanayagam and Osborne)

Ideas for longer activities, deeper engagement, and projects are listed in Subtopic 1.5 Taking action

Checking for understanding

Further exploration

Sources

Deivanayagam TA, Osborne RE (2023). Breaking free from tunnel vision for climate change and health. PLOS Glob Public Health 3(3). https://doi.org/10.1371/journal.pgph.0001684.

Earth for All. https://earth4all.life/

Meadows, D. H., & Randers, J. (2013). Limits to growth. Chelsea Green Publishing.

Raworth, K. (2017). Doughnut economics: seven ways to think like a 21st century economist. London: Penguin Random House

Richardson, K. et al. (2023). Earth beyond six of nine planetary boundaries. Science Advances, 9(37). DOI:10.1126/sciadv.adh2458

Shields, K. (Host). (2022). Tipping Point: The True Story of The Limits to Growth. https://tippingpoint-podcast.com/.

Terminology (in order of appearance)

Link to Quizlet interactive flashcards and terminology games for Section 1.2.7 Planetary boundaries


climate change: a change in the temperature and precipitation patterns in an area, in recent times due to human economic activities

economic growth: an increase in the total value of goods and services produced in a period of time

system: a set of interdependent parts that organise to create a functional whole

ecosystem: the interaction of a community of organisms with their physical environment

economy: all the human-made systems that transfer and transform energy and matter to meet human needs and wants

tipping point: a condition where even a small further change can push a system into a different state

planetary boundaries model: a model that illustrates these nine Earth systems and their limits

ocean acidification: a reduction in the pH of the ocean over time, caused primarily by absorption of carbon dioxide

global warming: the rise in the average temperature of Earth's air and oceans (due to human activities)

novel entities: things (mainly chemicals) created and introduced into the environment by human beings that could have disruptive effects on the earth system

stratospheric ozone: a naturally-occurring gas in the atmosphere that filters the sun's ultraviolet (UV) radiation

ultraviolet (UV) radiation: electromagnetic radiation from the sun with wavelengths of 10–400 nanometers

Montreal Protocol: an international agreement that protects the ozone layer by reducing ozone-depleting substances

aerosols: small solid particles or liquid droplets suspended in air

carbon dioxide (CO2): gas produced by burning carbon or organic compounds and through respiration, naturally present in the atmosphere and absorbed by plants in photosynthesis

carbonic acid: an acid formed when carbon dioxide dissolves in water

exoskeleton: a rigid external covering for the body in some animals

habitat: the natural home or environment of an animal, plant, or other organism

fertiliser: a chemical or natural substance added to soil or land to increase its fertility

phosphorus: an important element for living organisms as a component of adenosine triphosphate (ATP) which is the primary energy source for organisms' cells

nitrogen: an element that occurs as a gas which makes up 78 percent of the atmosphere and that forms a part of all living tissues

algae: a diverse group of aquatic organisms that conduct photosynthesis

surface water: water that collects on the surface of the ground, like lakes and rivers; also known as blue water

groundwater: water that collects underground in soil or in rock crevices and pores

stock: an accumulation of something, such as energy, matter, information, or money

flow: movement of something such as energy, matter, information or money between stocks

water cycle: the stocks and flows of all water on Earth

transfer: to move something from one place to another

transform: a change in the state, energy or chemical nature of something

energy: the ability to do work or cause change

matter: anything that takes up space and has mass

wetland: a distinct ecosystem flooded or saturated by water, either permanently or seasonally

extraction: taking something away from somewhere else, especially using effort or force

built environment: human-made structures or conditions in an area

biodiversity: the variety of living organisms on Earth

pollution: the presence of a substance that has harmful effects on the environment

sequester: to remove and store something