Planetary Boundaries: can there be limits to human growth?

A group of Earth system scientists in 2009 proposed a new framework of “planetary boundaries” that attempted to comprehensively consider every aspect of humanity’s transformation of the environment, from climate change to biodiversity loss. They wanted to establish an easily understandable guide to what was left of an optimum “safe operating space for humanity”. Beyond these boundaries, the researchers said, there is a risk of “irreversible and abrupt environmental change” that would make the planet significantly less habitable for humans.

The researchers, led by Johan Rockström of the Stockholm Resilience Centre and Will Steffen of the Australian National University, and including former NASA climate scientist James Hansen and Paul Crutzen, the atmospheric chemist and originator of the term ‘Anthropocene’, identified nine such boundaries. These also included ocean acidification, ozone depletion, the nitrogen and phosphorus cycle (the ‘biogeochemical boundary’), freshwater use, land use, atmospheric aerosols, and the ‘toxics’ boundary – meaning persistent organic pollutants, heavy metals, plastics and radionuclides. Due to the complexity of the Earth system, precise thresholds or tipping points are fiendishly difficult to determine, so Rockström and his colleagues instead speak of ranges, the bottom end of which is a particular boundary. And currently, two and a half of the boundaries – climate change, biodiversity loss, and the nitrogen cycle (but not the phosphorus cycle) – appear to have been crossed.

The concept in other words tells us how much more destruction of vital ecosystem services can we put up with before we begin to threaten the survival of our species. It is a map of the Anthropocene – a new geological epoch where humans are the main agent of change on the planet.

This new, rigorous framework has proven exceptionally popular, and has been endorsed by a range of international organisations such as the European Commission and the UN Environment Programme. The UK science journal Nature published a special edition of the publication featuring the report. From economist Jeffrey Sachs to noted architecture critic and artisanal cheese producer Prince Charles, it has been embraced by a panoply of global thought leaders and most green NGOs. A 2011 best-selling book by British environmental writer Mark Lynas, The God Species, riffed on and popularised the concept. No international environmental conference, whether focussing on government representatives, business leaders or activist groups, will fail to feature mention of the concept.

But this is not to say that everyone stands in agreement on its meaning, utility or how it is used. And there are many who question whether it is a worthwhile document at all. Fundamentally the debate centres on whether these boundaries represent rigid, permanent upper limits to human societal growth, or whether the lines are dynamic and the concept more a rule of thumb rather than immutably restrictive.

Scientists are cautious to define upper limits for environmental degradation

Even when it was launched, a number of researchers asked by Nature to comment on the concept said that while overall it was “worthwhile and useful”, they were also cautious about how to choose upper limits on environmental degradation and whether researchers know enough to choose the right parameters. To take the toxics threshold for example, few scientists are unconcerned about the effects of the wide variety of pollutants on biological organisms, yet at the same time, it seems difficult to quantify a boundary for this. The same can be said of atmospheric aerosols.

Tipping points are rarely predictable, and some worry that the idea allows us, like an undergraduate with a month before a paper is due, to say “Oh, well, we’ve got lots of time before things go pear-shaped! We don’t need to worry just yet.”

The concept has also generated unease over the implied prospect of global governance. As lead planetary boundary authors Steffen and Rockström state explicitly: “Ultimately, there will need to be an institution (or institutions) operating, with authority, above the level of individual countries to ensure that the planetary boundaries are respected. In effect, such an institution, acting on behalf of humanity as a whole.” They highlight one proposed institution as “global referee”:  an Earth Atmospheric Trust, “which would treat the atmosphere as a global common property asset managed as a trust for the benefit of current and future generations.” But how would the governors of such a trust be picked? Elected by the people of the Earth, or appointed by technocrats?

Others have a similarly fundamental worry that the concept smells a bit of Malthusianism – a rough grouping of ideas that argue that there’s only so much room on the planet, for a limited amount of people, and a limited amount of stuff. The ideology is named for Reverend Thomas Malthus, the 18th century economist who warned of an imminent crisis of overpopulation, famine and war if poor people continued to procreate.  He opposed laws providing relief for the poor, as this only encouraged them to breed, hastening the looming catastrophe, and instead argued that “unwholesome occupations”, vice, poverty and disease should be left to work naturally as a check on population growth.

Much later, the Green Revolution led by US biologist Norman Borlaug in the 1940s and 50s transformed agriculture via modern plant-breeding, irrigation infrastructure, synthetic fertilizers and pesticides. Scientists developed hybrid rice and wheat varieties that responded better to plant nutrients and grew with shorter, stiffer stalks to support the heavier heads of grain that produced higher yields. Agricultural productivity exploded in this period, simultaneously expanding the food supply and slashing prices.
Neo-Malthusians in the 1970s such as Paul Ehrlich with his best-seller The Population Bomb warned that acceleration in the world’s population was certain to produce global food shortages that would result in as many as four billion dead over the course of the 1980s. Four years after Ehrlich published his seminal tract, the Club of Rome think-tank, whose membership is composed of former heads of state, senior UN civil servants and business leaders, produced its own report based on then state-of-the-art computer modelling and funded by the Volkswagen Foundation, Limits to Growth, predicting similar civilizational “overshoot and collapse” from humanity breaching the Earth’s carrying capacity.

Many high-profile predictions of imminent collapse for humanity have proven spectacularly wrong

Yet the report and Ehrlich proved to be as spectacularly wrong as Malthus before them. By the end of the 20th century, almost all developed countries had seen a sharp drop in fertility rates as the result of the spread of effective birth control, but also as a result of economic development, education and the lower infant mortality that came with better healthcare. According to the Malthusian predictions, lower infant mortality was supposed to add to the population burden. Instead, as families now could be pretty assured that all their offspring would survive childhood, there was no need to have as many children. And what worries critics of Malthusianism – who historically have come from across the political spectrum: socialists and free-market advocates, feminists and human rights promoters – is that the planetary boundaries report was presented upon publication to the general assembly of the Club of Rome and is widely seen as a 21st century update to Limits to Growth.

A growing number of self-styled ‘eco-modernists’ such as the Breakthrough Institute, a US environmental NGO that, unlike many green groups, supports nuclear energy and genetic modification, disagree whether limits can truly have meaning for our species, given our historic ingenuity in the face of obstacles, or that the concept of carrying capacity can be applied to humanity. This population-biology term describes the speculative maximum, equilibrium number of organisms of a particular species that can be supported indefinitely in a given environment. A hundred-acre wood can support the consumption of a maximum of, say, 12 eeyores. Any more eeyores would require more acres of wood, or each of the eeyores consuming less.

The difference between humans and eeyores – or any other organisms – is that we can change the rate at which we use resources, either through technological advance or through changes to our political economy.

“Ever since early humans discovered fire and the benefits of collaborative systems such as collective hunting and social learning, human systems, not the classic biophysical limits that still constrain other species, have set the wider envelope for human population growth and prosperity,” argues ecologist Erle Ellis, an associate of the Breakthrough Institute. “It was not planetary boundaries, but human system boundaries that constrained human development in the Holocene, the geological epoch that we have just left. We should expect no less in the Anthropocene.”

The eco-modernists argue that the assessment of planetary boundaries is inherently political. Furthermore, they counter against the partisans of limits to growth that it is precisely through economic growth that humanity will be able to develop the new technologies and infrastructure that will enable us to solve the problems highlighted by the planetary boundaries concept like climate change and biodiversity loss. For them, the ‘hypothesis’ of planetary boundaries should rather be seen as a useful heuristic to inform policy-making rather than hard and fast limits, or worse, as ocean chemist Peter Brewer worried in a commentary in Nature on the concept: “just another stick to beat citizens with”. Speaking of the nitrogen cycle in particular, Brewer wrote: “it is likely that a large fraction of people on Earth would not be alive today without the artificial production of fertilizer … food is not optional.”

The debate thus is between those who want to retreat from the Anthropocene, and those who embrace our ascendence to, as Lynas puts it, a God Species.

To learn more, check out the Planetary Boundaries online-course starting mid-November, run by the Stockholm Resilience Centre and UN SDSN.


  1. Bernhard Wehrli

    “A safe operation space for humanity” requires peace. Armed conflicts definitely make this planet less habitable for humans. The concept of Planetary Boundaries focuses on environmental resilience. It deserves more support, but the same is true of any effort to improve social resilience.

Leave a Reply