The limits of the Earth - the planetary boundary model

Hi everyone,

So today we're talking about a model that was introduced in 2009 and has offered a new perspective to thinking about environmental issues.

The planetary boundary model has 9 boundaries, each has a safe zone. Once the safe zone is exceeded, the stable conditions on our planet are considered at risk, and there can be severe and possibly irreversible changes. The nine boundaries are considered separate however, they greatly affect each other.

Novel Entities describes the introduction and accumulation of man-made novel chemical compounds. These include pesticides, nuclear waste and microplastics.

Stratospheric Ozone Depletion refers to the depletion of the ozone layer which was a major problem in the 90s.

Atmospheric Aerosol Loading is air particle pollution.

Ocean Acidification is self-explanatory.

The boundary Biochemical Flows is composed of two separate boundaries; nitrogen and phosphorus. Both of the elements are vital for plant growth. They are therefore removed from the atmosphere/soil and turned into fertilisers which normally just wash away in the rain and pollute nearby waterways.

Freshwater Use is also split into two separate boundaries. The first is green water, which describes all water absorbed in soils, crops, plants and forests. This is sometimes called invisible water. The second is blue water, which describes water in rivers, lakes and streams, often known as visible water.

The process of turning natural habitats such as rainforests and grasslands into agricultural land is known as Land-System Change.

The two boundaries that make up Biosphere Integrity are functional and genetic.

The last boundary is probably the best known; Climate Change. Here there are two boundaries, CO2 levels and radiative forcing.

Planetary boundary model 2022

So now that we've covered the different boundaries, let's look at how much at risk they are of being exceeded. Here comes the sad news, six of the nine boundaries have now been crossed. Here's a brief overview of when which boundary left its safe zone. You can see these same years as a infographic here.

When introduced in 2009, biosphere integrity (at this point only one goal), climate change (also only one goal) and the nitrogen part of biochemical flows were already exceeded. Novel entities and atmospheric aerosol loading were not yet accessed.

In 2015, biosphere integrity was split into two boundries and land-system change and the phosphorus part of biochemical flows also left the safe zone. Novel entities and atmospheric aerosol loading still weren't accessed.

This year, 2023, all 9 boundaries were assessed for the first time. Climate change has been split into its separate boundaries, ocean acidification is worryingly close to leaving the safe zone. Both boundaries of freshwater use and novel entities have left the safe zone.

The only boundary which has got better is stratospheric ozone depletion. If this model had existed in the 1990s then the ozone depletion would have been out of the safe area. But regulations and initiatives have lead this boundary to now be the furthest from leaving its safe zone than all the rest.

One of the best things about this model is that it shows that the environmental crisis is so much more than just climate change. It shows how in every aspects, there is work to do and with the example of ozone depletion also shows that we can make a difference. We hope you enjoyed this post.

Your Green World Blog Team💚

Sources:
https://www.science.org/doi/10.1126/science.1259855
https://www.stockholmresilience.org/research/research-news/2023-09-13-all-planetary-boundaries-mapped-out-for-the-first-time-six-of-nine-crossed.html
https://planetaryinternational.com/2021/07/lets-discuss-the-9-planetary-boundaries/
https://www.stockholmresilience.org/research/planetary-boundaries.html

Image:
Designed by Azote for Stockholm Resilience Centre, CC BY-SA 3.0, via Wikimedia Commons

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