• Tracy Harfouche

What are the planetary boundaries and why are they important?

Throughout history, Earth has not been the same as we know it today. For the last thousands of years, the planet moved from the ice ages to enter a new era of stable climate and environmental conditions that helped humanity grow and develop. This interval in Earth’s history is called the Holocene. However, the progress that humanity knew hundreds of years ago came at the expense of the planet and made us start moving away from the Holocene conditions.


In 2009, an international team of researchers from the Stockholm Resilience Centre identified a set of nine planetary boundaries to define the environmental limits within which our actual quality of life could be retained. This concept provided a science-based analysis and quantitative measure of the risks of destabilising our Earth system.


To calculate and assess the impact of human actions on the environment, the planetary boundaries are defined in terms of control and response variables, with the first being the experimental element that is held constant during the study, while the latter is the result of the experiment whose variation is explained by other factors. As a result, scientists provided thresholds that humans should not cross to prevent dramatic consequences and irreversible environmental changes.


Unfortunately, 6 out of 9 of these planetary boundaries have been crossed until today.


Now let us briefly update you on the status of each planetary boundary:


The most updated version of the planetary boundaries’ status

Source: stockholmresilience.org


1. Introduction of novel entities into the biosphere

Novel entities (sometimes referred to as chemical pollutants) are known to be entities introduced by humans to the environment that can have turbulent effects on the Earth system. We are talking about plastics, pesticides, industrial chemicals, antibiotics, and others.


For years, this boundary was not quantified, and researchers couldn’t assess the impact of these pollutants on the planet given the huge amount of chemicals in circulation. In January of this year, a group of scientists made the evaluation and concluded that this boundary has been crossed.


“There has been a 50-fold increase in the production of chemicals since 1950. This is projected to triple again by 2050,” said one of the scientists from the Stockholm Resilience Centre. The study reveals that the total mass of plastics on the planet is now over twice the mass of all living mammals, while the production of plastic is expected to further increase in the future.


2. Stratospheric ozone depletion

The release of chemical compounds from industry and other human activities causes a diminished ozone layer. Because of that, increasing amounts of the sun’s damaging ultraviolet (UV) radiation will reach ground level, damaging human health as well as terrestrial and marine biological systems.


A thinning ozone layer, also known as the ozone hole, is considered from the moment the ozone concentration drops below 220 Dobson Units (DU) - where the average amount of ozone in the atmosphere is 300 DU, which is 3 mm thick. For instance, ozone depletion has been occurring over Antarctica annually during Spring since the 1980s.


In 1987, the Montreal Protocol was adopted to phase out the use of ozone-depleting substances and rebuild the ozone layer. Several international agreements with similar purposes were adopted later. Fortunately, in 2018, the United Nations confirmed that the ozone layer is recovering, which helped to remain within this boundary.


Source: Sciencefacts.net


3. Atmospheric aerosol loading

The atmospheric aerosol loading refers to the microscopic particles in the atmosphere that affect climate and living organisms. It was integrated within the planetary boundaries given its influence on the climate system as well as on human health.


Aerosols are tiny liquid droplets or particles that are suspended in the atmosphere. They can be natural like mist and dust, or anthropogenic like smoke and air pollutants. They can also affect cloud formation and patterns of atmospheric circulation, such as the monsoon systems. They change how much solar radiation is reflected or absorbed in the atmosphere. Sadly, pollution and land-use change have modified aerosol loadings.


To evaluate this boundary, researchers have used the south Asian monsoon as a case study and the aerosol optical depth (AOD) as the control variable. The limit was set at 0.25 AOD, with a zone of uncertainty between 0.25 and 0.50 AOD and the result came out over the south Asian region at 0.3 AOD. However, it was not possible to set a limit on the global scale, so we can say that this boundary has not been quantified yet.



4. Ocean acidification

As emissions keep on increasing, the ocean is now also absorbing large amounts of CO2, causing a progressive drop in the pH of ocean water. The absorption of CO2 by oceans is a natural phenomenon for ecosystems to stay balanced. However, due to an excess of CO2, this balance is now disturbed, causing ocean acidification.


It is still ambiguous to identify how organisms are affected by ocean acidification. However, scientists have determined that some species like corals, shellfish, and plankton can’t adapt to the new pH levels, which can cause radical changes to marine ecosystems and to the capacity of oceans to mitigate climate change. The threshold of ocean acidification shouldn’t fall below 80% of the pre-industrial aragonite saturation rate (a measure of carbonate ion concentration). According to the last time this rate was assessed, we are still within the limit at a rate of 84%.


Source: Sustainability.yale.edu


5. Biogeochemical flows (phosphorus and nitrogen cycles)

Biogeochemical flows refer to Nitrogen (N) and phosphorus (P) cycles, which are essential nutrients to grow plants. Unfortunately, human activity and industrialisation have altered the cycles of these two elements. Nitrogen is converted into new reactive forms that pollute waterways and coastal areas while phosphorus mobilised by humans enters aquatic systems and causes algae blooms.


The threshold of nitrogen is set between 62 and 82 teragrams per year (Tg N yr). In the last assessment made in 2015, the nitrogen losses were estimated at 150 Tg N yr.


The limit of phosphorus is divided into two:

- P global: P flow from freshwater systems into the ocean set at 11 Tg P yr. The 2015 assessment showed that this threshold was crossed at 22 Tg P yr.

- P regional: P flow from fertilisers to erodible soils set at 6.2 Tg P yr., which was as well exceeded at 14 Tg P yr.


6. Freshwater use

Water overconsumption for agriculture and industrial uses, waste, pollution, and other threats have severely affected the quality and abundance of freshwater around the world.


To assess this boundary, scientists used to evaluate the use of blue water only, which is the water in our surface and groundwater reservoirs. In April 2022, scientists integrated into their assessment, in addition to blue water, the use of green water, which is the water transpired by the plant that comes from rainwater stored in the soil.


Source: Researchgate.net


Scientists consider the consumptive use of blue water from rivers, lakes, reservoirs, and renewable groundwater stores as the global-level control variable to assess this boundary with a threshold value of 4000 km3/year. According to the latest assessment, we are withdrawing 2,600 km3 of blue water per year.


As mentioned, scientists reassessed the freshwater boundary this year and added a new subcategory: green water. “The green water planetary boundary can be represented by the percentage of ice-free land area on which root-zone soil moisture deviates from Holocene variability for any month of the year” scientists explained. The boundary for green water has in fact been crossed.


7. Land-system change (deforestation)

When humans decide to convert natural land into another type of land with different purposes (mainly for agricultural expansion), big modifications are made in the atmospheric carbon dioxide concentrations, which is later translated into changes in water flows, biodiversity, biogeochemical flows of elements, etc...


The limit of this boundary shows that the planet must preserve 75% of forested lands before starting to face irreversible consequences on biodiversity and ecosystems. Unfortunately, the latest quantitative assessment indicates that we crossed this limit by only maintaining 62% of these lands.


Scientists demand a boundary that does not only quantify the number of forests but also their function, quality, and geographical distribution to better evaluate the impact of land change on our planetary system.


To demonstrate the importance of this boundary, know that some forests, such as the Amazon, need to be sufficiently sound in order to maintain themselves. This means that if we pass the threshold, and deforest too much of the Amazon, the weather conditions that enable such a giant forest to exist will be destroyed and the rest of the forest will automatically disappear, no matter what we do.


8. Change in biosphere integrity

The impact of human activities on the functioning of the ecosystem has been seriously accelerating the loss of biodiversity and extinction of species. Scientists have divided this boundary into genetic diversity and functional diversity.


Genetic diversity, as its noun indicates, is the diversity of genes, which includes the different species as well as the differences in genes among the same species. Functional diversity on the other hand represents the role of the different species in the functioning of the ecosystem. For instance, two species can have the same impact on an ecosystem, like two types of pollinators. If one of these pollinators disappears while the second one grows enough to replace it, the functional diversity might be preserved while the genetic diversity will decrease.


It is hard to calculate the rate of extinction because no one has an exact number of species and new ones are discovered all the time. To evaluate genetic diversity, the threshold that should not be surpassed is 10 extinctions per million species-years (E/MSY). Today, experts estimate that we are between 1,000 and 10,000 E/MSY, which means we are losing species between 1,000 and 10,000 times higher than the natural extinction rate.


On the other side, the boundary for functional diversity has not been quantified yet on a global scale, while the biodiversity intactness index (BII) was set at 90%, with a range between 30-90%.



9. Climate change

The Climate Change boundary is by far the most known and talked about. It refers to the concentration of CO2 emissions causing global warming and activating extreme weather conditions and other climatic conditions. Measurements show that the concentration of CO2 in the atmosphere has surpassed 400 parts per million (ppm), which already exceeds the threshold of 350 ppm. This has already caused irreversible changes in our climate such as melting glaciers, increasing sea levels and extreme weather that impacts people's lives worldwide.



To sum up, the consequences of crossing the planetary boundaries might not be immediately visible to our eyes but definitely have a dangerous and irreversible impact on the interdependencies of ecosystems in the long term. Every day of inaction gets us closer to making Earth a less hospitable place.

To recover, we must learn to live in harmony with nature and keep its unpleasant sides under control. In doing so, it is important to look at all sides of the cube and try to remain within the set boundaries or minimise the crossed boundaries. Environmental challenges involve more than just climate change caused by carbon emissions; this is only the tip of the iceberg and there are several other boundaries to consider in order to avoid dramatic consequences.

If you are looking for advice on how to assess and manage the impact of your company’s activities on the environment, reach out to Flore Andersen, head of our Strategic Advisory team.

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