Virtually every past civilization has eventually undergone collapse, a loss of socio-political-economic complexity usually accompanied by a dramatic decline in population size [1]. Some, such as those of Egypt and China, have recovered from collapses at various stages; others, such as that of Easter Island or the Classic Maya, were apparently permanent [1,2]. All those previous collapses were local or regional; elsewhere, other societies and civilizations persisted unaffected. Sometimes, as in the Tigris and Euphrates valleys, new civilizations rose in succession. In many, if not most, cases, overexploitation of the environment was one proximate or an ultimate cause [3].
But today, for the first time, humanity's global civilization—the worldwide, increasingly interconnected, highly technological society in which we all are to one degree or another, embedded—is threatened with collapse by an array of environmental problems. Humankind finds itself engaged in what Prince Charles described as ‘an act of suicide on a grand scale’ [4], facing what the UK's Chief Scientific Advisor John Beddington called a ‘perfect storm’ of environmental problems [5]. The most serious of these problems show signs of rapidly escalating severity, especially climate disruption. But other elements could potentially also contribute to a collapse: an accelerating extinction of animal and plant populations and species, which could lead to a loss of ecosystem services essential for human survival; land degradation and land-use change; a pole-to-pole spread of toxic compounds; ocean acidification and eutrophication (dead zones); worsening of some aspects of the epidemiological environment (factors that make human populations susceptible to infectious diseases); depletion of increasingly scarce resources [6,7], including especially groundwater, which is being overexploited in many key agricultural areas [8]; and resource wars [9]. These are not separate problems; rather they interact in two gigantic complex adaptive systems: the biosphere system and the human socio-economic system. The negative manifestations of these interactions are often referred to as ‘the human predicament’ [10], and determining how to prevent it from generating a global collapse is perhaps theforemost challenge confronting humanity.
The human predicament is driven by overpopulation, overconsumption of natural resources and the use of unnecessarily environmentally damaging technologies and socio-economic-political arrangements to service Homo sapiens’ aggregate consumption [11–17]. How far the human population size now is above the planet's long-term carrying capacity is suggested (conservatively) by ecological footprint analysis [18–20]. It shows that to support today's population of seven billion sustainably (i.e. with business as usual, including current technologies and standards of living) would require roughly half an additional planet; to do so, if all citizens of Earth consumed resources at the US level would take four to five more Earths. Adding the projected 2.5 billion more people by 2050 would make the human assault on civilization's life-support systems disproportionately worse, because almost everywhere people face systems with nonlinear responses [11,21–23], in which environmental damage increases at a rate that becomes faster with each additional person. Of course, the claim is often made that humanity will expand Earth's carrying capacity dramatically with technological innovation [24], but it is widely recognized that technologies can both add and subtract from carrying capacity. The plough evidently first expanded it and now appears to be reducing it [3]. Overall, careful analysis of the prospects does not provide much confidence that technology will save us [25] or that gross domestic product can be disengaged from resource use [26].
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2. Do current trends portend a collapse?
What is the likelihood of this set of interconnected predicaments [27] leading to a global collapse in this century? There have been many definitions and much discussion of past ‘collapses’ [1,3,28–31], but a future global collapse does not require a careful definition. It could be triggered by anything from a ‘small’ nuclear war, whose ecological effects could quickly end civilization [32], to a more gradual breakdown because famines, epidemics and resource shortages cause a disintegration of central control within nations, in concert with disruptions of trade and conflicts over increasingly scarce necessities. In either case, regardless of survivors or replacement societies, the world familiar to anyone reading this study and the well-being of the vast majority of people would disappear.
How likely is such a collapse to occur? No civilization can avoid collapse if it fails to feed its population. The world's success so far, and the prospective ability to feed future generations at least as well, has been under relatively intensive discussion for half a century [33–40]. Agriculture made civilization possible, and over the last 80 years or so, an industrial agricultural revolution has created a technology-dependent global food system. That system, humanity's single biggest industry, has generated miracles of food production. But it has also created serious long-run vulnerabilities, especially in its dependence on stable climates, crop monocultures, industrially produced fertilizers and pesticides, petroleum, antibiotic feed supplements and rapid, efficient transportation.
Despite those food production miracles, today at least two billion people are hungry or poorly nourished. The Food and Agriculture Organization estimates that increasing food production by some 70 per cent would be required to feed a 35 per cent bigger and still growing human population adequately by 2050 [41]. What are the prospects that H. sapiens can produce and distribute sufficient food? To do so, it probably will be necessary to accomplish many or all of the following tasks: severely limit climate disruption; restrict expansion of land area for agriculture (to preserve ecosystem services); raise yields where possible; put much more effort into soil conservation [3]; increase efficiency in the use of fertilizers, water and energy; become more vegetarian; grow more food for people (not fuel for vehicles); reduce food wastage; stop degradation of the oceans and better regulate aquaculture; significantly increase investment in sustainable agricultural and aquacultural research; and move increasing equity and feeding everyone to the very top of the policy agenda.
Most of these long-recommended tasks require changes in human behaviour thus far elusive. The problem of food wastage and the need for more and better agricultural research have been discussed for decades. So have ‘technology will save us’ schemes such as building ‘nuclear agro-industrial complexes’ [42], where energy would be so cheap that it could support a new kind of desert agriculture in ‘food factories’, where crops would be grown on desalinated water and precisely machine fertilized. Unhappily, sufficiently cheap energy has never been produced by nuclear power to enable large-scale agriculture to move in that direction. Nor has agriculture moved towards feeding people protein extracted from leaves or bacteria grown on petroleum [43, pp. 95–112]. None of these schemes has even resulted in a coordinated development effort. Meanwhile, growing numbers of newly well-off people have increased demand for meat [44], thereby raising global demand for feedgrains.
Perhaps even more critical, climate disruption may pose insurmountable biophysical barriers to increasing crop yields. Indeed, if humanity is very unlucky with the climate, there may be reductions in yields of major crops [45], although near-term this may be unlikely to affect harvests globally [46]. Nonetheless, rising temperatures already seem to be slowing previous trends of increasing yields of basic grains [45,47], and unless greenhouse gas emissions are dramatically reduced, dangerous anthropogenic climate change [48] could ravage agriculture. Also, in addition to falling yields from many oceanic fish stocks because of widespread overfishing [49], warming and acidification of the oceans threaten the protein supply of some of the most nutritionally vulnerable people [50], especially those who cannot afford to purchase farmed fish.
Unfortunately, the agricultural system has complex connections with all the chief drivers of environmental deterioration. Agriculture itself is a major emitter of greenhouse gases and thus is an important cause of climate disruption as well as being exceptionally vulnerable to its consequences. More than a millennium of change in temperature and precipitation patterns is apparently now entrained [51], with the prospect of increasingly severe storms, droughts, heat waves and floods, all of which seem already evident and all of which threaten agricultural production.
Land is an essential resource for farming, and one facing multiple threats. In addition to the serious and widespread problems of soil degradation, sea-level rise (the most certain consequence of global warming) will take important areas out of production either by inundating them (a 1 m rise would flood 17.5% of Bangladesh [52]), exposing them to more frequent storm surges, or salinizing coastal aquifers essential for irrigation water. Another important problem for the food system is the loss of prime farmland to urbanization, a trend that seems certain to accelerate [53] as population growth steadily erodes the per capita supply of farmland.
The critical importance of substantially boosting the inadequate current action on the demographic problem can be seen in the time required to change the trajectory of population growth humanely and sensibly. We know from such things as the World War II mobilizations that many consumption patterns can be altered dramatically within a year, given appropriate incentives [54]. If food shortages became acute, then a rapid reaction would ensue as hunger became much more widespread. Food prices would rise, and diets would temporarily change (e.g. the number of meals consumed per day or amount of meat consumed) to compensate the shortage. Over the long term, however, expanding the global food supply and distributing it more equitably would be a slow and difficult process. Even though a major famine might well provoke investment in long-needed improvements in food production and distribution, they would take time to plan, test and implement.
Furthermore, agriculture is a leading cause of losses of biodiversity and thus of the critical ecosystem services supplied to agriculture itself (e.g. pollination, pest control, soil fertility, climate stability) and other human enterprises. Farming is also a principal source of global toxification, as has been clear since the days of Carson [55], exposing the human population to myriad subtle poisons. These pose further potential risks to food production.
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3. What needs to be done to avoid a collapse?
The threat from climate disruption to food production alone means that humanity's entire system for mobilizing energy needs to be rapidly transformed. Warming must be held well below a potential 5°C rise in global average temperature, a level that could well bring down civilization [56]. The best estimate today may be that, failing rapid concerted action, the world is already committed to a 2.4°C increase in global average temperature [57]. This is significantly above the 2°C estimated a decade ago by climate scientists to be a ‘safe’ limit, but now considered by some analysts to be too dangerous [58,59], a credible assessment, given the effects seen already before reaching a one degree rise. There is evidence, moreover, that present models underestimate future temperature increase by overestimating the extent that growth of vegetation can serve as a carbon sink [60] and underestimating positive feedbacks [61].
Many complexities plague the estimation of the precise threats of anthropogenic climate disruption, ranging from heat deaths and spread of tropical diseases to sea-level rise, crop failures and violent storms. One key to avoiding a global collapse, and thus an area requiring great effort and caution is avoiding climate-related mass famines. Our agricultural system evolved in a geological period of relatively constant and benign climate and was well attuned to twentieth-century conditions. That alone is cause for substantial concern as the planet's climates rapidly shift to new, less predictable regimes. It is essential to slow that process. That means dramatically transforming much of the existing energy mobilization infrastructure [62] and changing human behaviour to make the energy system much more efficient. This ispossible; indeed, sensible plans for doing it have been put forward [63,64], and some progress has been made. The central challenge, of course, is to phase out more than half of the global use of fossil fuels by 2050 in order to forestall the worst impacts of climate disruption, a challenge the latest International Energy Agency edition of World Energy Outlook makes look more severe [65]. This highlights another dilemma. Fossil fuels are now essential to agriculture for fertilizer and pesticide manufacture, operation of farm machinery, irrigation (often wasteful), livestock husbandry, crop drying, food storage, transportation and distribution. Thus, the phase-out will need to include at least partial substitution of non-fossil fuels in these functions, and do so without greatly increasing food prices. More
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