It is such a seductive idea at a time when environmental worries seem to be multiplying rapidly. So long as we keep the impacts of human activity within set limits we can carry on as we are without jeopardising the ability of Earth’s ecosystems to recover.
Breaching these “planetary boundaries”, goes the argument, takes us to tipping points – rapid and irreversible transitions to a world much less favourable to human existence. This school of thought combines the whiff of some serious mathematics – – with folksy wisdom that says “we’re safe, so long as we don’t cross the line”.
Alas, this is deeply flawed for several reasons. With more and more predictions of environmental doom and use of the boundaries idea to guide us, my colleagues and I felt the need to raise the alarm (Trends in Ecology and Evolution, ). First, there is no evidence that the natural systems in question work in this way and, indeed, there are compelling arguments that they cannot.
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The original idea of planetary boundaries involved looking at nine global, environmental processes affected by human actions, such as fresh water consumption, and the safe limits for them. One of those – the rate of species extinction – was argued to have broken the boundary value of 10 extinctions per million species per year and so was into tipping point territory.
Extinction rates , and when Al Gore talks about them being a thousand times faster than the natural, background rate of loss in his film An Inconvenient Truth, he is quoting work by me and my colleagues. There is no question that human actions are massively depleting the planet’s biodiversity. But does this mean planetary collapse is imminent?
An extinction rate is something that changes over time and is often far from global in its impact. So, in the minute when the heart of Martha, the last passenger pigeon, stopped, the extinction rate spiked. OK, so perhaps we must measure the rate over a decade, not a year, to set a better metric.
Species elimination
When Europeans reached many oceanic islands, it didn’t take them long to eliminate species, such as the dodo on Mauritius. The global, decadal extinction rates would have been very high, perhaps beyond a global boundary rate. But why should events in Mauritius affect ecosystems in, say, the remote Amazon?
Perhaps it isn’t the extinction rate, then, but the total loss of species in a given place that should be the measure. By now, the idea of a safe space based on extinction rates has lost all original meaning and what constitutes a boundary looks arbitrary and far from clear. In any case, we know a lot about what happens when species are lost from local areas. Certainly, there are local consequences, but they aren’t catastrophic in a wider sense.
Second, the boundary notion isn’t testable or applicable to the needs of those who manage nature. For instance, how do they measure a tipping point? And, given the idea’s problems, what do they measure? Tipping points add no useful insights.
Third, though surely well-intentioned, there is a powerful moral hazard in invoking boundaries and tipping points. They can lead to the creation of pernicious policies. Their appeal is powerful to those interests that are harming the planet and which wish to continue doing so. After all, if the planet hasn’t collapsed yet, we haven’t reached the acceptable limit, therefore there is scope to carry on.
What can we do? Undoubtedly, human actions harm biodiversity across the planet. The UN’s has defined rigorous targets to address these concerns, such as protecting 17 per cent of the land surface and 10 per cent of the oceans.
But some desirable targets beloved of environmental scientists are far less tangible – “sustainability”, “health”, “harmony” and others. These all speak to the urgent need to better understand how human impacts change ecosystems.
Boundaries, which lack credibility and don’t extend our understanding of complex systems, won’t address that need.
We have no choice but to work to understand those complex systems and turn that knowledge into practical solutions.
