The nine planetary boundaries

It is time we familiarise ourselves with the planet’s ecological ceiling in a year that has seen forest fires, heatwaves, flooding, and record-breaking land and sea surface temperatures

Photo by NASA on Unsplash

To stay healthy, we know there are certain things that are off limits. We know we shouldn’t eat beyond a certain amount, or there would be consequences. It could be stomach discomfort, heartburn or weight gain and other compounding issues in the long-term. Beyond food related limits, there are other conditions we should follow (but not limited to) such as exercising three times a week, sleep between 5–7 hours a day, and so on. We pay attention to these conditions to maintain our health.

Similarly with the Earth, it has boundaries, also known as ecological ceiling that must be adhered to to keep the biosphere healthy.

More specifically, our planet has nine planetary boundaries. Developed in 2009 by a group of scientists led by environmental scientist Johan Rockström and Will Steffen, the planetary boundaries are briefly explained below. You may be familiar with some of them while some may be something we tend to overlook in our busy day-to-day lives.

Climate change — When greenhouse gases such as carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O) are released into the air, they enter the atmosphere and amplify the Earth’s natural greenhouse gas effect, trapping more heat within the atmosphere. This results in global warming, whose effects include rising temperatures, more frequent extreme weathers, and sea level rise.

1. Ocean acidification — Around one quarter of the carbon dioxide emitted by human activity is eventually dissolved into the oceans, where it forms carbonic acid and decreases the pH of the surface water. This acidity reduces the availability of carbonic ions that are an essential building block used by many marine species for shell and skeleton formation. This missing ingredient makes it hard for organisms such as corals, shellfish and plankton to grow and survive, thus endangering the ocean ecosystem and its food chain.
2. Novel entities (chemical pollution) — When toxic compounds, such as synthetic organic pollutants and heavy metals, are released into the biosphere they can persist for a very long time, with effects may be irreversible. And when they accumulate in the tissue of living creatures, including birds and mammals, they reduce fertility and cause genetic damage, endangering ecosystems on land and in the oceans.
3. Biogeochemical flows (nitrogen and phosphorus loading) — Reactive nitrogen and phosphorus are widely used in agricultural fertilisers but only a small proportion of what is applied is actually taken up by crops. Most of the excess runs off into rivers, lakes and oceans, where it causes algae blooms that turn the water green. These blooms can be toxic and they kill off other aquatic life by starving it of oxygen.
4. Freshwater use — Water is essential for life and is widely used by agriculture, industry and households. Excessive withdrawals of water, however, can impair or even dry up lakes, rivers and aquifers, damaging ecosystems and altering the hydrological cycle and climate.
5. Land-system change — Converting land for human use, such as turning forests and wetlands into cities, farmland and highways, depletes Earth’s carbon sinks, destroys rich wildlife habitats, and undermines the land’s role in continually cycling water, nitrogen and phosphorus.
6. Biosphere integrity (biodiversity loss) — A decline in the number and variety of living species damages the integrity of ecosystems and accelerates species extinction. In doing so it increases the risk of abrupt and irreversible changes to ecosystems, reducing their resilience and undermining their capacity to provide food, fuel and fibre, and to sustain life.
7. Atmospheric aerosol loading (air pollution) — Micro-particles, or aerosols, emitted into the air, such as smoke, dust and pollutant gases, can damage living organisms. Furthermore, they interact with water vapour into the air and so affect cloud formation. When emitted in large volumes, these aerosols can significantly alter regional rainfall patterns, including shifting the timing and location of monsoon rains in tropical regions.
8. Stratospheric ozone depletion — Earth’s stratospheric ozone layer filters our ultraviolet radiation from the sun. Some human-made chemical substances, such as chlorofluorocarbons (CFCs) will, if released, enter the stratosphere and deplete the ozone later, exposing Earth and its inhabitants to the sun’s harmful UV rays.

The above summarisation of the nine planetary boundaries is taken from Appendix section of Doughnut Economics (2017).

Planetary boundaries transgressed (as of 2015)

As you may have guessed, humans have breached a few planetary boundaries already. Based on research in 2015, we have transgressed four out of the nine planetary boundaries (see Figure 1 below). The bold dotted line indicates the limits which should not be exceeded in order for humans to remain in a safe and just space.

Figure 1: The state of planetary boundaries as of 2015. Credit: J. Lokrantz/Azote based on Steffen et al. 2015

Note for Figure 1: E/MSY = extinctions per million species-years; BII = Biodiversity Intactness Index. At the time this data was published, E/MSY and BII are interim control variables until more appropriate variables are developed.

Further details of the value and trends of each planetary boundary are captured in Table 1. The third column shows the limit for each planetary boundary and the fourth column shows the current value as of 2015. As we can see from the table, we have already exceeded the limits for carbon dioxide emissions, phosphorus and nitrogen runoff from agriculture, the number of extinct species, and the area of deforestation.

Table 1: Value and trends of planetary boundaries in 2015 based on Steffen et al. (2015)

As if the 2015 results were not disturbing enough, new research have shown that six out of nine planetary boundaries have been transgressed. This despite the pledges by countries and businesses to reduce greenhouse gas emissions based on the Paris Agreement, and the adoption of other international agreements to halt deforestation and protect the planet’s biodiversity.

Planetary boundaries transgressed (as of 2022)

Novel entities

“Novel entities” was previously known as “chemical pollution”. when the concept of planetary boundaries was first introduced. Novel entities are defined as “new substances, new forms of existing substances and modified life forms”, including “chemicals and other new types of engineered materials or organisms not previously known to the Earth system as well as naturally occurring elements (for example, heavy metals) mobilised by anthropogenic activities”. Basically, new types of chemicals created by humans. The introduction of novel entities to the environment is of global concern due to its ability to spread with potential negative impacts on organisms and the planet’s natural systems and processes.

The production of novel entities is rapidly increasing; the chemical industry is the second-largest manufacturing industry globally. Global production has increased 50-fold since 1950, and is projected to triple again by 2050 compared to 2010. There are an estimated 350,000 chemicals (or mixtures of chemicals) on the global market. Nearly 70,000 have been registered in the past decade; with many chemicals (nearly 30,000) registered in emerging economies, where chemical production has increased rapidly, but the management and disposal capacity of chemicals are often limited.

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A study published in January 2022 found that increases in the production and release of novel entities are not consistent with keeping humanity within the safe operating zone. Due to the complex and diverse mechanisms that can capture the safe operating scope for novel entities, the authors of the studies used a set of control variables based on their feasibility, relevance and comprehensiveness. They are:

• the trend in production volume of chemicals;
• the trend in the production volume of plastics;
• the share of chemicals with safety data or regulatory assessments;
• the trend in emission quantities of hazardous chemicals;
• the trend in release quantities of plastics into the environment;
• the toxicity of chemical pollution; and
• the disturbance to the biosphere integrity of plastic pollution.

The fact that plastic make up three of these control variables shows how severe plastic pollution has become.

Figure 2 showcases the trend in the production volume of chemicals (the first bullet point above). High growth rates over the last couple decades can be observed for a number of novel entities which were selected based on publicly available production or production capacity data. Plastics is only second to the total chemical industry production.

Figure 2: Current rising global trends of chemical industry production, expressed as the relative growth in some novel entities between 2000 and 2017 (for when comparable data are available): 1. Global production capacity for the chemical industry as a whole, plastics production and pesticide active ingredients (for which earliest data are from 2008); 2. Per capita production capacity in weight for key monomers and solvents: benzene, butadiene, ethylene, propylene, toluene, and xylene, 3: Global consumption of antibiotics. Data from the Global Chemicals Outlook II, Geyer et al. 2017, and Søgaard Jørgensen et al 2020.

Despite major efforts in recent decades, the rapid growth in diversity, production volumes and releases outstrips the global and national authorities’ ability to assess, let alone manage novel entities.

Freshwater use

Water, particularly the rivers and ocean, have the limited ability to reduce the effects of chemical pollutants but humanity’s use of this essential life ingredient is putting another planetary boundary under pressure — freshwater use.

Before I go any further, let me explain the difference between “blue water” and “green water”. Within the water cycle, different colours of water can be identified, the two most important are blue and green. Blue water is the fresh water in streams, rivers, aquifers and surface water storage that sustains all freshwater aquatic biodiversity. Green water, on the other hand, is the soil moisture, flowing as evaporation and transpiration through plants, powering rain-fed food production and all living species in nature.

Humanity’s use of green water has apparently transgressed the freshwater use planetary boundary, according to a study published in April 2022. In this paper, the authors calls for renaming the “freshwater use” planetary boundary to “freshwater change” and that it comprises green water and blue water components. The study indicates the transgression of the green water component has taken place as indicated by the percentage of ice-free land area on which root-zone soil moisture deviates from Holocene-like conditions, together with the evidence of widespread deterioration in Earth system functioning.

Geologists measure time in eons, eras, periods, epochs and ages. The Holocene Epoch started about 11,700 years ago at the end of an ice age. Scientists are of the opinion that it was a time when Earth’s climate was relatively more stable and able to support contemporary human societies.

Scientists say we have now entered the Anthropocene Epoch due to humans’ lasting imprint on the planet ranging from the scattering of nitrogen from fertilisers, ash from coal, and plutonium isotopes from nuclear weapons. The name “Anthropocene” is derived from the Greek terms for “human” and “new”. This new epoch is believed to have started sometime between 1950 and 1954.

Within the planetary boundaries framework, boundary positions and transgressions of control variables are quantitatively assessed in relation to a baseline period, preferably the Holocene. In freshwater use planetary boundary, the green water planetary boundary is represented by the percentage of ice-free land area on which root-zone soil moisture deviates from the mid-Holocene (500 years~6,000 years ago) variability for any month of the year.

Soil moisture retention and availability are impacted by human activities and can be defined as surface soil moisture, total soil moisture column and root-zone soil moisture. The root-zone is defined as the depth of soil at which the plant roots exploit water, with different types of vegetation exhibiting different rooting depth. The water stored in the root-zone layer is one of the most important water resources, as it supplies natural vegetation and crops with the vital water needed. Mechanistically, root-zone soil moisture is most directly linked to transpiration, biomass production and soil moisture drought and therefore, the best candidate for freshwater use planetary boundary control variable.

In the chart below (Figure 3), scientists used the following control variable: the percentage of ice-free land area on which root-zone soil moisture anomalies go beyond the local bounds of baseline variability in any month of the year. The use of upper and lower bounds accounts for both wet and dry departures from the mid-Holocene baseline. These local bounds are defined as the 5th and 95th percentiles of root-zone soil moisture for a given month for all years within the baseline period.

Figure 3: Percentage of land area with monthly root-zone soil moisture deviations beyond local lower (dry departure) and upper (wet departure) bounds. Source: Wang-Erlandsson, L., Tobian, A., van der Ent, R.J. et al (2022).

Since around 18% of land area currently lies outside local bounds, the green water planetary boundary is taken to be considerably transgressed. This assessment is further motivated by the overall increasing trend of human influence on green water and the fact that green water modifications are likely to progress further before any trend reversals can be observed due to inertia in the Earth’s system.

So, we have breached six out of nine planetary boundaries (see Figure 4), albeit two of them partially (freshwater use and biosphere integrity). It could be that humans may well have transgressed more than that, but have yet to quantify it. Of course, current research comes with their uncertainties but we should always err to be on the safe side. With temperatures this summer being termed as the dawn of global boiling, the amount of carbon dioxide absorbed by the ocean will undoubtedly increase, potentially leading to higher rates of ocean acidification. If we haven’t already breached this planetary boundary, it is probably nearing it.

Time for farsighted policymaking

There is no use looking back to the good old days of the Holocene now that we are in the Anthropocene. What we can do is to ensure policies regulating just about every aspect of our lives are crafted with the end goal of bringing humanity back to within the planet’s safe operating zone. Policies related to everything from the economy to agriculture, forest, wetlands and ocean management, chemical and plastic production, development, and many more will need to be amended. If we are not in any position to make those decisions, we will need to make it known through our voices and our choices.

For instance, economist Kate Raworth came up with the concept of doughnut economics in 2012 (I love doughnuts, by the way). What’s interesting about doughnut economics is that it rethinks the way the economy works by incorporating the nine planetary boundaries. It lays out the foundation of how the economy can work while ensuring that everyone is within the Earth’s safe operating zone. I plan to write about the doughnut economics in another article but you can read about it here first.

Photo by Shayna Douglas on Unsplash.

I brought up doughnut economics as an example of how we, not matter our profession, or where we are, can think of ways we can incorporate the planetary boundaries in our lives. Yes, the onus is on policymakers and businesses to take the lead but at the same time, we can figure out what we can do.