In my last post on the environmental footprints of meat and other foods, I discussed the major environmental impacts of the most common animal- and plant-based foods that we eat for protein. This post will examine the environmental issues in more detail – the major threats to life on Earth known as Planetary Boundaries. I know, who wants to hear more about environmental issues? But this will be objective and ultimately optimistic – besides, aren’t you curious about what made it onto the list? It’s like The Oscars for the planet!

The term planetary boundaries comes from an international group of scientists who have defined nine major threats to life on planet Earth and metrics for each of them. To describe them, I’ll focus on their 2023 paper, Earth beyond six of nine planetary boundaries.

The Epochs Tour: From the Holocene to the Anthropocene

The authors of the paper describe how global environmental conditions have been quite stable since the end of the last ice age, around 12,000 years ago – which marked the beginning of our Holocene epoch – all the way up to the industrial revolution. For example, Earth’s mean surface temperature varied by only around 0.5°C, and biomes have been quite stable during that period. We are all pretty familiar by now with efforts to keep the global mean surface temperature from rising more than 1.5°C, or 2.0°C tops. So, no prizes for guessing that (spoiler alert!) climate change is one of the nine planetary boundaries (of course it is).

The planetary boundaries framework draws upon Earth system science. It identifies nine processes that are critical for maintaining the stability and resilience of Earth system as a whole. All are presently heavily perturbed by human activities

Human activities have now brought Earth outside of the Holocene’s window of environmental variability, giving rise to the proposed Anthropocene epoch.

The authors point out that respecting the planetary boundaries would allow “life-support system to remain similar to those experienced over the past ~10,000 years rather than changing into a state without analog in human history.”

Entering a state never encountered before might sound like an adventure, but unfortunately it won’t be a pleasant one for most (except maybe for cockroaches and rats and very rich people such as Elon Musk). Not that I’ve anything against cockroaches or rats…

What are the planetary boundaries?

The main figure from the 2023 Planetary Boundaries paper is the best way to describe them and show which have been transgressed. As you can see below, there are nine main divisions and four of them have been split into two subcategories.

So the three status categories for each boundary are safe operating space, zone of increasing risk, and high risk zone. To make them a little less confusing, I’m going to rename the last two as highway to the danger zone, and the danger zone. You’re welcome!

Let’s run through the planetary boundaries, starting at the top and going clockwise:

1. Climate change

Status: Highway to the danger zone

You’re familiar with this one, so I won’t say too much about it here. But as a quick reminder, here’s a chart from NASA showing how the amount of CO₂ in our atmosphere stayed within certain limits for around a million years, never exceeding 300 ppm (0.03%) until around the year 1911. Its rise over the last century has been alarming (but also predictable) and now exceeds 420 ppm.

If you’d like to learn more about climate change, I recommend starting with the most recent reports from the Intergovernmental Panel on Climate Change (IPCC) – Part 1, Part 2, and Part 3. I’ll return to climate change as we go on.

2. Novel entities

Status: Danger zone

This is the only planetary boundary that’s not so clearly defined, but that is also the point – we don’t know what the biggest threats are. The scientists broadly define the threat under the umbrella of synthetic chemicals and substances (e.g., microplastics, endocrine disruptors, and organic pollutants) that are released without adequate safety testing. They also cite past examples such as the insecticide DDT and the chlorofluorocarbons (CFCs) that damaged the ozone layer. One set of synthetic chemicals that I believe should be highly restricted are the bestselling insecticides known as neonics – they pose a significant global risk by killing pollinators and other species. (See, for example, this risk analysis of Bayer’s imidacloprid.)  

The next planetary boundary (ozone depletion) serves as a good example of how novel entities can cause unexpected harm.

3. Stratospheric ozone depletion

Status: Safe operating space

This threat stands out as one that we have navigated fairly successfully, thanks to global efforts such as the 1989 Montreal Protocol to phase out ozone-depleting chemicals (mainly chlorofluorocarbons, or CFCs). It’s also a good example of how we can put the planet in peril for thoughtless stuff that’s not important – remember all that hairspray everyone was using in the eighties? Or, to put it another way, stuff that was produced in thoughtless ways, when there are better ways to package hair product and deodorant.

Have some things improved?

This brings up a question: Were the greed-is-good 1980’s a low point for humanity, when it comes to consumer behavior? I find it helpful to look at Hans Rosling’s work – his book, Factfulness, and his entertaining talks. As Dr. Rosling pointed out, many things such as sanitation and education in the Global South have been generally improving over time. I do think that consumer awareness is improving but that there are blips and reversals along the way – as Newton found, every action has an equal but opposite reaction. Yes, there are trends right now towards self-centered madness (a bit like the 80’s) that threaten to take Planet Earth further beyond these boundaries. But the pendulum will swing again and maybe we will find balance and happiness in simplicity.

It’s certainly encouraging that we have succeeded in halting destruction of the ozone layer. Of the nine planetary threats, ozone depletion is one of three that are currently in the safe zone (although the ozone layer is still weak at Southern high latitudes).

The story of CFCs and their successors illustrate how novel entities can become planetary threats. It took quite some time to prove that CFCs were a threat to the ozone layer, by which time they were considered essential as refrigerants. HFCs (hydrofluorocarbons) were adopted as the main alternative to CFCs, despite skepticism at the time about replacing one class of synthetic chemicals (not found in nature) with another. HFCs, although safe for ozone, turned out to be bad news for climate change, being extremely potent greenhouse gases.

Well, thankfully, researchers (some at Greenpeace, actually) found safer, commonly occurring chemicals that can replace HFCs as refrigerants. It’s only recently that we have the option to buy fridges and freezers containing these green refrigerants. Why didn’t we have that option earlier? Mainly because companies can get away with the use of risky synthetics for decades, knowing that it can take that long for publicly-funded scientists to demonstrate that they are unsafe.

4. Atmospheric aerosol loading

Status: Safe operating space

Atmospheric aerosol loading basically translates to air pollution that reduces the amount of sunlight reaching the earth. A good amount of the dust particles in the air come from natural sources (desert dust, soot from wildfire), but that’s not to say that they are independent to human activity. The drying out of the Sahara and other deserts and the increase in wildfires are largely due to climactic changes such as altered rainfall patterns. 

This is another planetary boundary that’s currently in the safe zone on a global level. But tell that to people who live in areas that experience chronic air pollution . Air pollution is the second leading cause of death, after high blood pressure, being responsible for roughly 8 million of the 62 million deaths that occur on Earth, each year. There are also large impacts on land and marine ecosystems.

Everything is interconnected!

One thing to note here: many of the planetary boundaries are interconnected in some way. For example, changes in land use such as the burning of peatlands for palm oil plantations or rainforest for beef production significantly exacerbate both climate change and atmospheric aerosols (air pollution). In turn, climate change can dry out land and increase desertification, causing the release of more dust into the air.

Therefore, many of the solutions also overlap – such as avoiding the destruction of forest and peatlands or reducing fossil fuel use. The introduction of clean cooking solutions in the Global South is a top solution for mitigating both climate change and air pollution as it reduces the release of black carbon into the atmosphere.

5. Ocean Acidification

Status: Safe operating space (but approaching the highway to the danger zone)

This is the third of the boundaries that’s still in the safe zone, but not by much.

Anthropogenic ocean acidification currently lies at the margin of the safe operating space, and the trend is worsening as anthropogenic CO₂ emission continues to rise. – From the 2023 paper, Earth beyond six of nine planetary boundaries.

The increase in atmospheric CO₂ levels that drives climate change also results in an increase in dissolved oceanic CO₂. This increase in dissolved CO₂ causes a reduction in ocean water pH (acidification) that interferes with many aspects of ocean life.

Marine calcifying organisms, such as mollusks and corals, are especially vulnerable because they rely on calcium carbonate to build shells and skeletons. – Wikipedia.

So a reduction in greenhouse gas (GHG) emissions will help reverse both climate change and ocean acidification. One of the best consumer actions for mitigating both problems in a way that directly targets acidification and ocean health is to consume more seaweed.

6. Biogeochemical flows (phosphate and nitrogen pollution)

Status: Danger zone

The major chemical elements in life forms such as humans and plants are carbon, hydrogen, oxygen, nitrogen and phosphorus (CHONP). Most of the carbon originates from photosynthesis (fixed by plants, some of which are eaten by humans and other animals) and most of the H and O atoms come from water, which leaves the N and P. As farming expanded and intensified to match human population growth, the use of fertilizer to supplement the soil with N and P has increased.

This planetary boundary is defined as the imbalances in the nitrogen and phosphate cycles, with excess ending up in oceans. It originates from mainly from heavy fertilizer use, fish farms, and animal waste run off into rivers. This causes water pollution (eutrophication) that robs the ocean of oxygen, killing fish and other lifeforms. A well-known example is the dead zone in the Gulf of Mexico, which results from nitrogen and phosphate carried down rivers from American Midwest farms. The amount of eutrophication caused by food production varies considerably by food type, as discussed in the last post on the environmental footprints of protein-rich foods. Here’s a quick reminder of that:

Nitrogen and phosphate pollution is deep into the danger zone, so here are a few actions that can help mitigate it:

• Avoid the foods with a very high eutrophication footprint, shown in the chart above: beef and farmed fish.
• Minimize consumption of foods with a moderately high footprint: lamb, cheese, and pork.
• Consume mainly plants such as legumes (which fix their own nitrogen from the air), grains, fruit, and veggies.  
• Choosing organic food helps too – see this post on nitrogen use for organic versus conventional bread.

7. Freshwater change

Status: Highway to the danger zone

This planetary boundary on water use is divided into the human disturbance of blue water and green water flow and availability. Blue water is the water stored in lakes, rivers, reservoirs and underground aquifers that serves as our main sources of water for drinking and irrigation. Green water is the water available to plants from precipitation (rain, snow), stored in root and soil systems.

Agriculture uses about 70% of our blue water, so consuming food with a smaller water footprint is one of the most effective actions we can take as consumers. Organic agricultural practices such as the use of cover crops can help preserve soil moisture outside of the main growing season. When the cover crops are legumes, they also help deposit nitrogen to the soil, reducing the need for fertilizer.

Regional transgressions of planetary boundaries

This is a good time to bring up the fact that the transgression of planetary boundaries can be local to specific regions. For example, freshwater use is in the danger zone such as California and Spain, two regions that have also experienced wildfires and droughts recently. Here’s a thought: let’s stop buying bottled water; an industry founded on the exploitation by multinational corporations of aquifers that should be available to locals.

8. Land system change

Status: Highway to the danger zone

(In the danger zone for some regions, e.g., Amazon rainforest)

The land system change planetary boundary refers to the destruction of forests for human use. Oxford University scientists Poore and Nemecek (whose paper I covered in the last post) examined deforestation for agriculture and found that most (67%) of it takes place for meat production. In their last report, the IPCC emphasized the critical impact of deforestation (they use the term land use change) on climate change. As a way of examining our impact as consumers, in my last post, I showed Poore and Nemecek’s data on the land footprint of individual protein-rich foods.

I plan to focus on the topic of land use change in my next post as it’s a big one. Briefly, some products are specific threats to our forests because of where they’re grown – for example, palm oil, chocolate, and coffee. In some cases, the threat to the forest is hidden in the supply chain – this applies especially to crops used as animal feed. The more universal rule is that, since land is a highly limited resource, any product with a large land footprint threatens the forests that are essential to the integrity of our biosphere.

9. Biosphere integrity

Status: Danger zone

Biosphere integrity is measured by a combination of genetic diversity and planetary function, both of which are now in the high risk zone. Here’s a quick description of these terms and how they are measured:  

Genetic diversity is measured by the rate of species extinctions. The current extinction rate is estimated to be somewhere around 100 times faster than normal. The authors say that the boundary was already transgressed by the late 19th century when large-scale changes in land use (deforestation) took place.

Of an estimated 8 million plant and animal species, around 1 million are threatened with extinction, and over 10% of genetic diversity of plants and animals may have been lost over the past 150 years.

Planetary function is measured by human appropriation of the biosphere’s net primary production (HANPP). NANPP is basically a measurement of what percentage of the planet’s biomass is grown for human needs (food and textile crops, etc.). See my post on cellulose for a little more information on net primary production.

Consider that photosynthetic organisms capture an estimated 250 billion tonnes of CO₂ each year and store it as biomass. This is known as net primary production (NPP). – Why is cellulose so important?

As mentioned above, the biosphere integrity boundary is closely linked to land use change (land system change) as more land appropriated for human needs means less available for other species. Several of the planetary boundaries are not only closely connected but are also largely driven by a single lifestyle choice.

Planetary Boundaries: connections and causes

As the authors of the latest planetary boundaries paper point out that they are “systemically linked risks” and therefore warrant even more caution as they can exacerbate each other. Changes in land use have major impacts on both biosphere integrity and climate change. Climate change is also a major direct threat to biosphere integrity, plus the higher CO₂ levels that cause climate change also cause ocean acidification. Changes in freshwater availability are obviously closely interlinked with climate change, too.

But we can see even more connections when we look for single human activities that have contributed significantly to the transgression of several boundaries. Any activity that causes the emission of CO₂ and other GHGs will of course impact climate change and therefore ocean acidification and biosphere integrity. But there’s one single activity that has played a major role in driving us past several boundaries at once: meat production.

Beef production, in particular, has been and continues to be a major driver of imbalances in 6 out of the 9 planetary boundaries. The data is all laid out in the previous post on the environmental impacts of meat and other foods, so I won’t repeat it all here.

I’ll wrap this up with a figure that summarizes the interconnectedness of our environmental challenges and major cause.

Food production (agriculture) is a major factor in almost every global environmental challenge that we face. We need to eat, of course, but some foods have much smaller environmental footprints so the solution is simply a matter of giving preference to those foods. Let’s be glad that there is such a simple solution!