MarkWhen a population grows beyond the resources available to sustain all the individuals, it has reached an ecological overshoot—too many individuals for the available resources.
Ecological theory has it that density-dependent mechanisms that increase mortality and reduce fertility due to competition as resources become limiting will slow population growth to avoid this situation otherwise, the population risks extinction from over-exploitation. If you are of the selfish gene persuasion, then genes prefer to avoid competition unless they can win.
In the 1980s, I studied this phenomenon for my PhD research. I worked on populations of a woodlouse, the common pillbug Armadillidium vulgare, and spent hundreds of hours weighing the young the females produced after messing with the mother’s diets. There is good evidence that these simple terrestrial crustaceans respond to competition. Nature is remarkable.
So when we see the massive population spike in the most intelligent, ubiquitous and successful great ape, Homo sapiens, it begs the question of ecological overshoot and if the rules of density dependence apply.
Humans on the brink
Back in 2005, American academic and author Jared Diamond wrote a book called Collapse: How Societies Choose to Fail or Succeed that defined collapse as “a drastic decrease in human population size and/or political/economic/social complexity, over a considerable area, for an extended time.”
Diamond examined the stability of several past and present human societies relative to environmental fragility, relations with neighbours, political institutions, and other “input” variables. He concluded that the collapse of the Maya, Anasazi, Easter Islanders and other past societies began only a decade or two after the society reached its peak numbers, wealth, and power because of population size, wealth, resource consumption, and waste production meant environmental impact outstripped resources.
In short, an ecological overshoot was the precursor to collapse.
The population grows on the back of available resources, and then one or more of them are used up as consumption continues until there was not enough resources to go around. This concept is familiar to any student of ecology.
A population of organisms is only as large as the available resources permit. If reproduction delivers more individuals than available energy, nutrients or space can support, they compete with each other in a scramble or a contest.
Not every individual wins enough resources to compete, so the reproductive rate and survivorship in the population slow. In time, numbers decline until they drop below the resource base again.
Ecologists call this density-dependent population regulation.
Genes prefer density-dependence to deliver population regulation. In their selfish way, they persist into the next generation only if the vehicles they are in survive to reproduce successfully. If overshoot happens, there is a risk that the scramble for resources kills off the entire population.
Intelligent readers will realise that this is one of the reasons why selfish gene theory is attractive to humans. It assumes that evolution favours regulation. And if that assumption holds, overshoots are more likely to be modest and recovery likely.
Jared Diamond reminded us in Collapse that humans can easily overshoot to excess, just as we do most things.
Humans are so ecologically competitive, including competitive displacement and extending the resource base through technology and access to exogenous energy—fossil fuels—that we ignore density dependence. Instead of being limited by overshoot, we simply use up resources.
We quickly assume that the laws of nature do not apply to us. We can have dominion and look forward to limitless economic growth.
So how close are we to ecological overshoot?
Humanity is already at an ecological overshoot
Here is what the earth overshoot looked like in 2022 as estimated by the Global Footprint Network summarised for various countries by Statista.
Date when the annual renewable resources are used up is calculated from a population’s demand for and ecosystems’ supply of resources and services. Supply represents the renewable resources from biologically productive land and sea area, including forest lands, grazing lands, cropland, fishing grounds, and built-up land. Demand calculates the plant-based food and fiber products, livestock and fish products, timber and other forest products, space for urban infrastructure, and forest to absorb its carbon dioxide emissions from fossil fuels. Supply and demand are expressed in global hectares—globally comparable, standardized hectares with world average productivity.
Bangladesh makes it to Boxing Day, whilst Australia, despite being a whole continent, is done before easter.
Globally, humanity makes it to 28 July 2022 on naturally renewed resources. The rest of the year, we mine the non-renewable capital.
When did ecological overshoot start?
According to Diamond, population and societal collapse will happen a few decades after reaching peak numbers. This makes sense because competition for limited resources would take some time to translate into fewer births and more deaths—nuclear holocaust notwithstanding.
Humans are technologically advanced, and this skill makes new resources available and increases efficiency in resource use, as well as moving existing resources around. This makes the point when resources become limiting challenging to predict or to determine if we have passed it already.
Here is one estimate with demand and supply balanced in 1970 and overshoot consistent and growing since then.
Date when the annual renewable resources are used up is calculated from a population’s demand for and ecosystems’ supply of resources and services. Supply represents the renewable resources from biologically productive land and sea area, including forest lands, grazing lands, cropland, fishing grounds, and built-up land. Demand calculates the plant-based food and fiber products, livestock and fish products, timber and other forest products, space for urban infrastructure, and forest to absorb its carbon dioxide emissions from fossil fuels. Supply and demand are expressed in global hectares—globally comparable, standardized hectares with world average productivity.
If we assume this estimate is sound, then we have already had a few decades and our numbers should be falling due to lower birth rates and higher death rates.
Globally, birth rates are declining but not by enough—the population is still growing at 8,000 per hour—and since 1970 the population has more than doubled.
When will ecological overshoot end?
More people, more consumption and ever more significant overshoot.
The economic system can leverage energy inputs and technology—what Nate Hagens calls our fossil fuel slaves—into food and people. The subsidy keeps us all going untethered from the ecological limits.
Optimists and economic theorists believe that this energy and technology subsidy is the human superpower that allows us to ignore resource constraints. So long as there is energy to power our infrastructure and grow food, all is well. Overshoot can continue to happen without consequence.
Realists know that this is crazy talk.
Even if new energy sources are invented and deployed to replace the polluting fossil energy, sooner or later, we run out of raw materials, space, nutrients, or water or drown in an ocean of waste products.
On the current path, overshoot ends with collapse—the unknown is when this will happen.
What sustainably FED suggests
There is no doubt that humans have decoupled from ecological constraints thanks to our access to fossils and technologies that provide us with a vast army of ‘slaves’ to do all our heavy lifting. For now, we have excess energy above what nature can supply directly.
What we are not decoupled from is the physical resources, especially water, metals and materials that we use to produce food and infrastructure.
Then come the tough questions.
Could we start with WTF? Or perhaps more politely, what are we thinking?
Clearly humanity is on borrowed time and resources, and there is not enough ecological capacity within the planet to maintain current levels of energy and resource use and absorb the waste it generates. It is not about paying back what we have borrowed but just slowing down to take a breath.
Here are five more nuanced questions borrowed from William E Rees, Professor Emeritus at the University of British Columbia and former director of the School of Community and Regional Planning.
- What weaknesses inherent in existing ‘environmental economics’ actually facilitate ecosystem degradation and overshoot?
- Can the damaged exosphere sustainably support yet another two billion humans plus a doubling of GWP and various forms of energy/material demand, as is expected by mid-century?
- What eco-economic tools and policies help might maintain a satisfactory quality of life while implementing a planned contraction of planet-depleting economic activities and populations?
- What circumstances promote people’s capacity for cooperation, community building and short-term sacrifice to achieve mutually beneficial future ends (e.g., survival)?
- How can ecological economics help identify efficient policies to regenerate key ecosystems and maintain essential life-support functions, including a predictably stable livable climate?
Our answers.
- We are oblivious to the ecological consequences of our economic system even as we stay wedded to it on our endless path to development.
- No, the biosphere cannot support our current path.
- How about universal food income? More on this later.
- Ironically, collapse.
- Start with soil carbon sequestration and a reduction in fertilizer use.
You can browse the rest of the sustainably FED for more answers and ideas. We have over 100 posts to choose from.
Science Source
Rees, W. E. (2020). Ecological economics for humanity’s plague phase. Ecological Economics, 169, 106519.
Hero image from photo by ask mediendesign from Pixabay
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