"In the forests of Laos and Vietnam, few animals heavier than 80 grams can now be found". (from Stokstad E: The empty forest. Science (2014) 345(6195):396-399.)
Limits to growth, planetary boundaries, and planetary health
For submission to Current Opinion in Environmental Sustainability by Oct 1, 2016 (update December 28, 2017: it was published, though slightly different to this version)
Colin D Butler1,2
This paper presents an overview of the “Limits to Growth” debate, from Malthus to Planetary Boundaries and the Planetary Health Commission. It argues that a combination of vested interests, inequalities, and cognitive impediments disguise the critical proximity to limits. Cognitive factors include an increasingly urbanized population with declining exposure to nature, incompletely substituted by the rise of simulated and filmed reality.
Following prominence in the 1960s and early 1970s, fears of Limits to Growth diminished as the oil price declined and as the Green Revolution greatly expanded agricultural productivity. While public health catastrophes have occurred which can be conceptualised as arising from the exceeding of local boundaries, including that of tolerance (e.g. the 1994 Rwandan genocide), these have mostly been considered temporary aberrations, of limited significance.
Another example is the devastating Syrian civil war. However, rather than an outlier, this conflict can be analysed as an example of interacting eco-social causes, related to aspects of limits to growth, including from climate change and aquifer depletion. To view the “root causes” of the Syrian tragedy as overwhelmingly or even exclusively social leaves civilization vulnerable to many additional disasters, including in the Sahel, elsewhere in the Middle East, and perhaps, within decades, globally.
An aspect of the Limits to Growth debate that was briefly prominent was “peak oil”. Fear of this has fallen with the oil price. But this does not mean that Limits to Growth are fanciful or will apply only in the far future, even if (which seems unlikely) the oil price remains low. The proximity of dangerous climate change is the starkest example of an imminent environmental limit; other examples include declining reserves of phosphorus and rare elements. Crucially, human responses have the capacity to accelerate or delay the consequences of these limits. Greater understanding of these issues is vital for enduring global population health.
Keywords: Anthropocene, civilization collapse, climate change, conflict, environmental determinism, human carrying capacity
On world refugee day, 2016, the United Nations High Commission for Refugees announced that at the close of 2015 there were over 65 million displaced people on the planet (the majority of whom afire children), an increase of over 50% from the end of 2011 . This increase is neither random nor coincidental, but a foreseeable consequence of planetary scaled socio-ecological (or “eco-social”) factors. Unfolding for decades, these forces continue to evolve in broadly predictable ways. The growing number of refugees (11.7 million in 2015 from Syria alone, now 1 million from South Sudan) shows the failure of the current world political system and the wishful bias of many policy makers and academics. The global progress that was, until recently, widely predicted  may be unravelling .
There are a few prominent exceptions, most notably Paul and Anne Ehrlich [4,5], but most commentators still remain optimistic. The most recent median projection for the size of the global human population in 2100 is of over 11 billion people, approximately 3.5 billion more than today. Average life expectancy at birth in 2100 is forecast to have risen 13 years above its recent (2010-2015) level of 70 years . The Sustainable Development Goals are similarly confident . Instead, humanity needs to appraise its stocks and prospects, environmentally and socially. The threats to civilisation may be higher than most experts and governments acknowledge .
Emergence, environmental determinism, or “risk multiplication”?
Instead of viewing the catastrophe in Syria  as either an aberration or random, it can be conceptualized as a “canary case” of emerging “regional overload” . An increasing number of authors [10-14] have argued that climate change aggravated the Syrian drought, in turn worsening aquifer depletion, also contributed to by ongoing population growth . All of these analysts are very clear that these environmental stressors do not act alone to cause conflict, but interact with an established, fluid milieu whose elements include inter-group rivalry, resentment, unfair governance, inequality and outside interference.
Yet most political scientists reject the claim of a significant contribution from anthropogenic climate change to existing and future conflict . Attempts to link ecological and social factors with conflict have even been denigrated as “environmental determinism” , a philosophy whose origins have been traced to Baron de Montesquieu in 1748 . In this perspective, social and historical phenomena are allegedly “controlled” by environmental factors, with little if any appreciation of the wider social and political context within which conflict may emerge. However, evidence of the existence of simplistic cases of environmental determinism in the recent peer reviewed literature is easier to allege than to locate.
Denial of an environmental contribution to conflict appears also to discount systemic, emergent theories of causation, where many factors coalesce, but where few are necessary or sufficient [18,19]. Additionally, “political” factors, identified by some as of greater importance than environmental determinants  are themselves often inextricably blended with ecological elements, such as long-standing grievances due to displacement from favoured, resource rich locations.
An alternative way to conceptualize the influence of environmental change upon phenomena such as conflict, migration and famine is to consider factors such as drought as “risk multipliers” (or dice-loaders), rather than “event deciders”. Using this conceptualization, many phenomena are “eco-social” rather than purely social or ecological, a causal model that also implies that the solutions to many dilemmas (including conflicts) are neither exclusively social nor environmental.
The high rate of human population growth in Syria (although declining, the total fertility rate before the war was still far above replacement)  played a role, not only by accelerating local resource depletion, including of groundwater, but by reducing the “demographic dividend”, a benefit which helps to promote economic and human development . One harmful consequence of the high fertility rate in Syria was high youth unemployment, reported as 48% in 2011, at the onset of the war, a fivefold increase from 2000 . In turn, large numbers of young, underemployed, unfulfilled men (sometimes called “youth bulges”) have been linked to violence .
Malthus, Limits to Growth and limits to transparency and compassion
The intellectual underpinnings of the emerging global eco-social crisis include Thomas Robert Malthus, The Limits to Growth, Planetary Boundaries and the Planetary Health Commission. Malthus (1766-1834) is mainly remembered for his prediction that human population growth (unless slowed by means such as delayed marriage) would growth in food supply growth, leading to reductions in living standards and (eventually) human population size. But the most fundamental contribution of Malthus was the idea that individuals and species, including humans, compete for scarce resources. Undoubtedly ancient, this insight was so well popularised by Malthus and his supporters that the key developers of the theory of evolution, Darwin and Wallace, each acknowledged their debt to him .
Soon after Malthus’s death the Irish famine was interpreted as supporting his central thesis . Critics of Malthus instead pointed to the primacy of social, political and economic factors, particularly inadequate relief from England. However, these elements can also be accommodated into a broad interpretation of Malthus’s central idea (see Figure 1), including a limited willingness to provide relief. The Irish famine emerged from multiple factors, two of which were high population growth and high population numbers . In turn, these influenced other causal elements of the famine, such as reliance by the poor on an affordable but ultimately highly vulnerable potato monoculture.
During the Irish famine (1848-1852), population roughly halved, due to deaths from famine and diseases with large-scale migration. The proximal cause was the potato blight, but this was exacerbated by minimal famine relief. During the famine, grain continued to be exported from Ireland. This lack of relief by Britain or any other power does not negate Malthus’s central concept.
The term “limits to growth” became popular following publication of the book of that name in 1972 . Using a systems approach, it presented a computerized model of the interconnected  global eco-social system. This work concluded that environmental decline, combined with accelerating population growth and resource scarcity, had the capacity, without reform, to precipitate civilization collapse by 2100, rather than by 2000 as many of its critics erroneously claimed .
Initially regarded with esteem, including by US President Carter  the influence of the Limits to Growth waned, due to the rise of neoliberalism and the success of the Green Revolution . This backlash was also associated with the “cornucopian” doctrines of social scientists such as Julian Simon, who argued for laissez faire population growth, claiming that additional people were the “ultimate resource”, and thus to be welcomed anywhere and any time [25-27].
An important aspect of limits to growth theory is the decline in energy return on energy investment (EROEI) . Although wind and solar power are increasingly important, these technologies still have a low EROEI. The decline in easily recoverable oil helped stimulate the oilsands boom and fracking, but the ingenuity each exhibits has not solved fundamental problems such as leaking greenhouse gases, especially methane, associated with fracking .
The fall in the price of oil since its two crests in 2008 and 2010 has led some commentators to argue that “peak oil” concerns have been overstated. However, few experts argue that the current comparatively low oil price will persist for more than a few more years. But even if abundant fossil fuel reserves are discovered, their exploitation is limited by the imperative to slow carbon dioxide (CO2) accumulation . The maximum tolerable level of greenhouse gases in the ocean and atmosphere, quickly approaching , constitutes another limit to growth. Other environmental limits include of crop yields , phosphate reserves (essential for agriculture) , rare earths, helium, and some metals . Ecosystem change is also limited , as are innovations such as Moore’s Law .
There are also limits to manageable complexity [3,37], as well as to co-operation, compassion and aid. People are rarely transparent, especially in milieux in which others are perceived as deceptive. Relatedly, distrust of recipients limits generosity and assistance, and also means, in many cases, that human population size over extended periods is lower than possible were inter-group co-operation much higher (see figure 2).
Populations can be conceptualised as inhabiting a “safe operating space” (SOS) some of which is used (the blue circles) by an area proportional to population, affluence and technology, and an unoccupied area, a “reserve” safe operating space (SOS). In scenario A, there is very little reserve SOS, but little significant conflict, nor migration or premature death. In scenario B, there is a greater reserve of SOS, but total population*affluence is not maximised, due to distrust and conflict, such as in Syria or South Sudan. The 2007-10 drought in Syria reduced the area of the box, reducing the reserve SOS and increasing the risk of conflict.
Humans evolved to co-operate in small groups, themselves in competition with similarly co-operating groups . Although honesty within one’s close group may be rewarded, openness and trust of rival group members, especially if competing , is unlikely, and could even be hard-wired. Can humanity broaden its conception of self-interest to the entire species? If so, can humans preserve sufficient ecosystem services to guarantee safety?
Planetary Boundaries and Planetary Health
The term “planetary boundaries” defines a “safe operating space” for humanity [40,41]. Like the Anthropocene and the Earth system, these terms recognise and reflect the global scale of human biosphere alteration . Planetary boundaries are not located at postulated critical biophysical thresholds, but up-stream, providing a safety margin of uncertain size.
The initial formulation of planetary boundaries included nine Earth system processes, each modified by human action. The processes which have led to the proximity to planetary boundaries have helped humanity to reach its current level of dominance, but these processes have now “overshot”. The passing of most planetary boundaries will not necessarily reveal new health risks, but if sufficient boundaries are exceeded profound effects to the Earth system will be triggered, with profound adverse flow-on effects to health and other aspects of human well-being .
In 2014 the Planetary Health Commission (supported by the Rockefeller Foundation and The Lancet) was established to explore the significance of these ideas to health . The Commission sought also to investigate how global health has improved despite an eroding environmental foundations, deciding “the explanation is straightforward and sobering: we have been mortgaging the health of future generations to realise economic and development gains in the present”.
Cognitive Factors and Inequality as Barriers to Sustainability
Millennia ago, the reliance of all humans on the environment is likely to have been apparent from an early age, even though numerous past populations did great ecological harm, at least locally, as people transformed their surroundings for perceived human benefit [44,45]. It is plausible that this sense of human-nature connection began to decline as agriculture was increasingly adopted, accompanied by the rise of urbanization and industrialization. Today, more than half of the world’s almost 7.5 billion people are urbanized. For affluent and influential populations, food is available in abundance, yet an increasing number of such people have scarcely any personal experience of growing food. Many such populations are also likely to be personally insulated from the stress, harm and risk of high ambient temperatures and humidity, each likely to worsen significantly in many areas due to global warming [46,47]. The rise of simulated and filmed nature may also be contributing to an erosion of popular understanding of civilisation’s risk, disguising the extent of harm that has already accrued, and contributing to the extent of cognitive dissonance .
The phrase “the 1%” reflects the rise of inequality in the US and many other countries . Excessive unfairness reduces resilience and increases the risk of collapse [3,50]. The most affluent people on Earth not only have the greatest privilege but the most political influence . Many decision makers are likely to be disproportionately protected from other direct adverse effects of global environmental change, including extreme events such as flooding, but may be more vulnerable to highly indirect “tertiary” (systemically arising) effects of adverse eco-social change including conflict, mass migration and even terrorism [52,53].
A distinguished and growing number of scientists, futurists and policy makers, including the governor of the Bank of England, have warned that current dominant practices will place civilization at risk, via pathways that include nuclear war . A breakdown in global public health, leading to increased epidemics, on a background of deteriorating eco-social phenomena that damage health determinants is also a plausible scenario . Today, humans prey on nature. Although Pinker and others argue that violence by humans against humans has declined , the violence of our species against nature is rising. This cannot continue. These challenges, created by our species, may still be soluble, but this will require far more honesty, courage, understanding, human resources and high level attention than has recently been made available. It also requires greater openness and sharing.
Acknowledgements: Many thanks to Dr Kerryn Higgs for her helpful comments.
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