planetary boundaries

The nine boundaries | Day 181

How do we know when we have irreparably screwed up our planet?

According to a team of environmental scientists from the Stockholm Resilience Centre and Australian National University, there is a framework for that.

In collaboration with 26 leading academics, in 2009 the team introduced the Planetary Boundaries framework which identifies critical thresholds or limits in nine planet-scale life support systems essential for the survival of humans as a species.

Transgress them, and the results are likely to be catastrophic.

In a paper in Ecology and Society, the authors pointed out that recognising planetary boundaries can help shape discussion on the way forward. At the time of publication, three of the nine boundaries had already been overstepped.

In mid-January this year an international team delivered an update on this framework with a paper published in Science. As of this year, we can add another transgression to our legacy. I think we need to work harder on that discussion.

The nine planetary boundaries

So what are these boundaries, and which ones have we overstepped already?

  1. Ozone depletion. As demonstrated by the Antarctic ozone hole, once the ozone layer is depleted, damage to humans and biological systems on the planet is dire.

    This boundary is measured by the stratospheric ozone concentration.
    Have we crossed it? Not yet.

  2. Change in biosphere integrity (biodiversity loss). In the past 50 years humans have changed their environment more rapidly than ever before due to increasing demands for food, water, and natural resources. This leads to profound ecosystem changes.

    This boundary is measured by the number of extinct species per million per year.
    Have we crossed it? Yes.

  3. Introduction of novel entities (pollution). Toxic and long-lived substances, such as micro-plastics, nanomaterials, heavy metals, synthetics and radioactive materials are a key driver of human-induced planetary environmental change. Their effects on the Earth system are moribund, however it is not yet clear how this boundary could be quantified.

    Have we crossed it? We don’t know.

  4.  Climate change. It seems that we are way past recovering this one, and are pushing several thresholds already. For example, according to the researchers, we have reached a point at which the loss of summer polar sea-ice is almost certainly irreversible.

    This boundary is measured by atmospheric carbon dioxide concentration.
    Have we crossed it? Yes.

  5. Ocean acidification. Roughly a quarter of the carbon dioxide that we emit eventually dissolves into the world’s oceans, forming carbonic acid and significantly changing the chemistry of ocean water. This has knock-on effects on marine species, the loss of which would eventually change the dynamics of ocean systems with ramifications on a global scale.

    This boundary is measured by the global mean saturation state of aragonite in surface seawater.
    Have we crossed it? Not yet.

  6. Freshwater consumption. We build dams, alter the course of rivers and exert numerous other changes on water systems, causing irreversible changes in how freshwater is distributed across the globe.

    This boundary is measured by global human consumption of water per year.
    Have we crossed it?  Not yet.

  7. Land use. Converting wast tracts of diverse vegetation types into agricultural land has impacts on several planetary boundaries, such as water flow, biodiversity loss, and others. The land and the climate are intertwined, and chopping down forests inevitable causes disruptions.

    This boundary is measured by the percentage of our planet’s land surface that’s been converted to cropland.
    Have we crossed it? Not yet.

  8. Biogeochemical flows (phosphorus and nitrogen cycles). Both of these elements are essential for plant growth, so human use of fertilizers is causing an overabundance of nitrogen in the atmosphere, and of phosphorus in the water, subsequently polluting the various systems the elements end up in.

    This boundary is measured by anthropogenic nitrogen removed from the atmosphere and anthropogenic phosphorus going into the oceans, in millions of tonnes per year.
    Have we crossed it? Yes.

  9. Atmospheric aerosol loading. Inorganic or organic particles suspended in our planet’s atmosphere have a direct impact on the climate and can shift weather patterns. However, their behaviour is so complex that many causal links are yet to be determined, and for now there is no quantification for this boundary.

    Have we crossed it? We don’t know.

So, what does all this mean?

According to co-author Johan Rockström, it’s time we make some decisions on a global scale.

“It is obvious that different societies over time have contributed very differently to the current state of the earth. The world has a tremendous opportunity this year to address global risks, and do it more equitably. In September, nations will agree the UN’s Sustainable Development Goals. With the right ambition, this could create the conditions for long-term human prosperity within planetary boundaries.”

Head to the planetary boundaries website to explore this topic in more depth and learn about the various interactions between the boundaries, as well as their individual importance.


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