Planetary boundaries: a safe world for humans?


The planetary boundaries represent conditions that enable humans to live safely and comfortably on the planet. So far, humans have thrived and now rule the world. We want to continue to thrive, but it is only possible if natural systems are not pushed beyond the critical tresholds or tipping points. 

Text: © 2020 Kathelijne Bonne 

A safe space is in this context is not about war vs. peace, or poverty vs. prosperity (despite also needing urgent action). It is about chemical conditions that are favorable for a human body to function on Earth, the only place in the universe where human life is possible, as far as we know. This environment has a happy combination of a food pyramid, water, oxygen, bearable temperatures, and generally a resilient natural habitat. 

The concept of planetary boundaries is based on the idea that such conditions can reach limits when faced with environmental changes. The concept was proposed by scientists working in the Stockholm Resilience Center in Sweden. The United Nations now include this concept in the implementation of the Sustainable Development Goals (SDGs). The idea is that planetary boundaries are used as a framework for an improved stewardship of the planet. 

What is a planetary boundary?

The boundary or limit can also be described as a tipping point or threshold: The value at which a very small increment for a variable (e.g. a small increase in CO2) triggers a larger, possibly irreversible catastrophic change in the response variable (e.g. global warming). It is the moment at which the Earth system cannot absorb a change without undergoing profound change. It is literally the straw that breaks the camel's back. 

Stability and resilience

In 2009 the Stockholm scientists defined nine processes that regulate the stability and resilience of the Earth system. They proposed measurable planetary boundaries within which humanity can continue to prosper for generations to come.

The nine processes and the way they are measured are: 

  1. Climate change (in CO2, in parts per million)
  2. Biodiversity loss (number of extinct species per million per year)
  3. Biogeochemical cycles (nitrogen removed from the atmosphere, and phosphorous going to the oceans, in millions of tonnes per year)
  4. Ocean acidification (measured by calcium carbonate saturation state)
  5. Land use (percentage of land surface converted to cropland)
  6. Freshwater (human consumption, in cubic kilometers per year)
  7. Ozone depletion (stratospheric ozone concentration)
  8. Atmospheric aerosols (particulate concentration)
  9. Chemical pollution (Concentration of toxic substances, plastics, endocrine disruptors, heavy metals, and radioactive substances)

Today, we are still within safe operating limits for five of the nine planetary boundaries. The idea is to get back into safe limits for all processes. 

It is well known that Earth systems, including climate, temperature, ocean acidity and atmosphere oxygen levels, oscillate over long timespans. This means they naturally undergo change, an argument often used by skeptics who prefer 'business as usual' over action to be taken for a more sustainable way of life. 

One can argue that life as a whole has shown to be resilient because it has already prospered for 4 billion years. This indeed required a certain overall stability: Past climate changes have apparently occurred within safe limits. On the other hand, we also do know that many species died out, because the naturally changing environment is almost never safe for all species. For example, global ocean acidity has been responsible for the extinction of 90% of all species at a given time in the geological past. And the species alive today are only a fraction of all species that ever lived, do to frequent extinctions. On top of that, most natural climate changes have occurred at much lower speeds, e.g. ten of thousands to millions of years, than the current anthropogenic climate change (since the Industrial Revolution).

Human actions

Human actions have increased the rate at which Earth systems undergo change. CO2 in particular is produced at an unnatural rate. But Earth is an interconnected system, and oceans try to absorb the excess CO2. As a consequence, global water bodies become increasingly acid. This could push the Earth systems out of the safe limits and causing irreversible change to the ecosystems and food pyramids humans rely on.

Luckily for us, some countries and many scientists are scrutinizing the details of the planetary boundaries. We can only keep our fingers crossed that policymakers will listen to them, but they must do so quickly. And for now, as citizens, we can think about what can be done, and implement small actions for a better future. 



The website of the Stockholm Resilience Center

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