In nature, any successful species can overshoot a habitat, consuming resources faster than Earth’s ecosystems can replenish them. On Earth today, indicators such as species extinctions, soil loss, and global warming – tell us that humans have reached this state of overshoot on a global scale. In seeking solutions, we may benefit from some historical perspective.
University of British Columbia professor Dr. William Rees and his colleague Mathis Wackernagel originated the “ecological footprint” analysis, now universally used to measure personal, family, or regional ecological impact. Rees estimates that humans now use about fifty percent more resources in a year than Earth can replenish. In 2010, Rees wrote “The Human Nature of Unsustainability” for the Post Carbon Reader, explaining some of the evolutionary reasons that our “reasonably intelligent species” appears unable to recognize its ecological crisis or respond accordingly.”
Rees explains that humans share with all species two behavioural traits critical to evolutionary survival:
1. Expand to occupy all accessible habitats, and
2. Use all available resources.
“These propensities toward overshoot,” says Rees, “are playing out on the global scale today.”
Humans are what biologists call “K-strategists.” The “K” stands for a habitat’s carrying capacity, which large mammals tend to fill with relatively-stable populations, restrained by predators and food supply. For such animals, habitat capacity limits may favour short-term, individual gratification (for food, sex, etc.). These traits have survival value, but only until the species overshoots its habitat capacity. Thereafter, as Rees explains, “behavioural adaptations that helped our distant ancestors survive... become maladaptive.”
Dr. Kathy McMahon, a clinical psychologist, who tracks stories of environmental trauma, understands the ecological crisis, but believes we need to summon our “better angels” to help us survive and prosper. She agrees with Rees about destructive habits, but asks: “Do we not have within us, the very innate altruistic qualities needed to work our way back to that simpler, communally-focused way of life ... that will bring us back to our senses?”
McMahon asks: “ ... How do we find the sane space between Doom and Denial? Is blind optimism itself, a diagnosable mental disorder?” To build a sustainable future, it may help to understand something of our history.
The Dawn of Unsustainability
As long as humans relied on their own physical power to collect food, our ancient ancestors did not overshoot their habitats. Other predators and habitat capacity acted as restraints on growth, even after humans developed tools. Unsustainable human expansion appears in the historical record once humans gained access to “exosomatic energy” or “exoenergy” – energy from outside their own metabolism and nature’s growth cycles. The significant exoenergy sources in human history that led to habitat destruction include controlled fire, animal power, cultivated agriculture, slaves, and fossil fuels.
Comparing human population growth rates will help us understand the progress of human overshoot. Once Homo erectus communities began to control fire in the mid-Pleistocene, about 500,000 years ago, they gained the exoenergy that allowed them to expand beyond the capacity of their habitats. By 200,000 BC, only a few thousand humans lived on Earth (see population sources below), and their annual growth rate remained below one-thousandth of what it is today, around 0.001%, a 70,000-year doubling time, a very slow growth. By 40,000 BC, aided by controlled fire, modern Homo sapiens population had reached about 300,000, the growth rate had tripled to about 0.003%, and the doubling time fell to 20,000 years. Anthropologists find evidence, during this era, of large-scale human-induced animal and plant extinctions. Controlled human fire appears to be the primary cause.
For example, around 47,000 BC, humans arrived in Australia and large animals (mammals, 19 marsupials, 3 large reptiles, and most flightless birds) all vanish. Research conducted by Dr John Magee, Dr Michael Gagana and others shows that emu diets suddenly changed from vast plant varieties to a few shrubs. The explanation: Humans regularly set fire to the landscape to flush out prey.
The burning destroyed species directly and caused climate change by reducing water vapour flow between biosphere and atmosphere. Cloud cover declined, the monsoon cycle was broken, the Nullarbor grassland and forest (with tree-dwelling Kangaroos) became desert scrub, and once abundant Lake Eyre became a salt flat. Similar extinctions occurred almost everywhere humans migrated.
About 75% of North America’s megafauna (mastodons, mammoths, giant beavers, bears, sabre-toothed tigers) perished as humans advanced into their habitats. Some 30 species of megafauna disappeared in South America. When humans arrived in Madagascar, only 2,000 years ago, every mammal over 20-pounds disappeared (pygmy hippos, lemurs, and others.). Human communities in Hawaii quickly eradicated 90% of all bird species, and in New Zealand exterminated 11 Moa species in 100 years.
We learn evolutionary “success” has costs, and without restraints, those costs can be fatal to even the “successful” species.
Mining the soils
By 10,000 BC, Homo sapien population had grown to about 4.5 million, the growth rate increased 7-times in 30 millennia to 0.02% and the doubling rate fell to 3-thousand years. It helps us understand our modern predicament to realize that with this growth rate, humans were already unsustainable. At a 3-thousand-year doubling time, human population would have reached our modern 7-billion in a little over 30,000 years – instead of 12,000 – but still would have reached it. This tells us something about what the right solutions will look like. The answer to overshoot is not a particular level or style of technology, but rather achieving a stable growth pattern, which in nature means a cyclical growth pattern, a dynamic stability within an environment, which in ecology we call “homeostasis.”
After 10,000 BC, animal husbandry and crop cultivation provided humanity with two new sources of exoenergy, animal power and soil mining. Some indigenous cultures in the western hemisphere learned to replenish soils, utilizing legumes to fix nitrogen and applying seaweed and fish to replace nutrients. It is possible to create a permanent agriculture, but these systems imply limits to community growth. Those societies that simply mined their soils suffered devastating results.
Soil microbiologist Peter Salonius traces “irreversible degradation of arable soil productivity… to the advent of cultivation agriculture.” Productive soils, as modern permaculture research shows, need interdependent ecosystems to recycle nutrients, nitrogen, phosphorus, potassium, calcium, and other compounds. Early slash and burn agriculture disrupted these natural systems. Intense cultivation and irrigation in Mesopotamia, for example, left depleted, salted soils. Entire civilizations collapsed.
One of human society’s earliest extant stories – the Sumerian Gilgamesh from 2500 BC – chronicles forest depletion and ponders the ethics of deforestation. Humans with goat herds and hand axes converted the Syrian/Lebanon cedar forests to desert.
During this stage of human history, social elitism in human communities appears to have overwhelmed our “better angels,” our cooperative, egalitarian, respectful, and modest lifestyles. Hierarchies developed that controlled land, conquered neighbours, and took slaves (another form of exoenergy that allowed rulers to dominate more people and more land).
By 400 BC, human population had reached 160 million, the growth rate reached 0.13%, and the doubling time fell to only 525 years. Forest and soil destruction soared, proved unsustainable, and led to a massive collapse.
Growth stops and restarts
In 430 BC a plague swept Athens, marking a profound shift in human growth patterns. By 100 AD, for the first time in human history, the human growth rate turned negative. Humans were dying off, due to overcrowding, disease, crop failure, warfare, and genocide. It took almost 2,000 years for humanity to recover and sustain its 400AD growth rate.
During this period, the Chinese began burning coal, the dawn of the hydrocarbon era. In both Asia and Europe, coal powered new migrations, colonization, and more plunder. Once again, increased exoenergy fuelled massive growth, and in this case, industrial growth. Around 1810, the human population reached a billion people, and then added another billion in a century. The annual human population growth rate peaked in 1963, at 2.2%. The fastest billion people were added between 1985 and 1997 (12 years and 2 months!) The most humans ever added to Earth in one year, 1989, is 87 million! The growth rate is now half its peak, 1.1%, but we still add some 77 million humans each year, equivalent to ten cities the size of London.
Today, most humans eat negative-net-energy food provided not from soil, but mostly from oil. Most world agriculture now runs on hydrocarbons for land clearing, tilling, harvest, fertilizer, transport, and packaging. To achieve this, we have burned the best half of recoverable hydrocarbons in one century, launching a new climactic era of rapid heating.
We need to shift quickly from hydrocarbons to low-carbon energy sources to avoid drastic global warming, but history also shows that unless we slow our consumption and growth trends, more energy cannot really save us.
In the essay “Future Scenarios” in Sustainability or Collapse? An Integrated History and Future of People on Earth (R. Costanza, et. al., 2007), the authors warn: “Even when a collapse is known to be imminent, it often cannot be controlled, and recovery cannot occur until considerable reconfiguration and downsizing has taken place.”
Here is where we must summon our “better angels” in the search for an appropriate scale of human activity “It is now time,” Kathy McMahon says, “for careful thinkers to propose an alternative view of what it means to be fully human. We may need to look outside The First World for new insights and broader understandings.”
- Rex Weyler, December 2011
Deep Green is Rex Weyler's monthly column, reflecting on the roots of activism, environmentalism, and Greenpeace's past, present, and future. The opinions here are his own.
Population estimate sources: Hyde (2006), Maddison (2003) Biraben (1980), Durand (1974), McEvedy & Jones (1978), Thomlinson (1975), Livi-Bacci (2001), Carl Haub (2005), K. W. Harl, Kremer (1993), Tanton (1994), US Census Bureau (2008), Population Reference Bureau (2005); UN: 1973, 1999, 2006. All figures are approximate.
Image: Artist John Quigley: ""We came here and created ‘The Melting Vitruvian Man’, recreating da Vinci's famous sketch of the human body, because literally climate change is eating into the body of our civilisation. When he did this sketch it was the Enlightenment, the Renaissance, the dawn of this innovative age that continues to this day, but our use of fossil fuels is threatening that." Image: Nick Cobbing/Greenpeace