Overshoot is a phenomenon that happens to some species. Under conditions of overshoot, a population exceeds its sustainable carrying capacity in its environment. What happens as a result is that the population eventually crashes. To make matters worse, it’s often possible that the effects that a species has while it exceeds its carrying capacity ensure that its carrying capacity actually declines.
How can this happen? Let’s take a herd of deer on an island. The deer depend on a resource that regenerates (plants). It’s possible for the deer to eat more plant biomass than is regenerated in the same period. This is temporarily sustainable, just like spending more money than earning money can be sustained for a while.
What happens however when the deer eat too many plants is that the regenerating capacity of the plants on the island is affected, as two plants can produce more new biomass to keep deer alive than one plant can. This thus suddenly reduces the actual carrying capacity of the deer.
In addition, changes to the ecological community may happen that ruin the carrying capacity of the island for a much longer period. A particular species of plant that does better on certain parts of the island than other species do may be eaten into extinction. Large areas of the island may have no plants growing at all, ensuring that the soil blows away.
It’s clear that overshoot conditions are potentially dangerous to the survival of an ecological community. It therefore shouldn’t come as a surprise that nature has a lot of mechanisms in place that reduce the ability for a species to enter overshoot conditions. Parasites, germs, predators as well as biological mechanisms present within the species itself can serve to keep a species from reaching overshoot conditions. An example of the latter would be an animal that becomes infertile because its body fat percentage is too low.
In an isolated community, not all these mechanisms may be present. If someone thus came across an island with a deer population in overshoot, the most merciful thing to do would be to kill a large number of them, which is what hunters in the United States are forced to do with deer, as a consequence of their lack of predators.
History has shown that humans are capable of reaching overshoot conditions as well. In some cases, this has permanently reduced the carrying capacity of a local environment. A good example would be Iceland.
When the Vikings arrived, a quarter of the island was covered with forests. The Vikings cut down the forests. Besides causing soil erosion, the albedo of the island changed, which had the effect of reducing temperatures. Thus, with the forests gone, the conditions that enabled the growth of the forest were gone as well, making it very difficult to reforest the island.
Iceland’s carrying capacity had been greatly reduced. As a result, Iceland’s population always remained low. In 1095 the population was 77,500, which dropped to 72,000 by 1311. By 1703, the island’s population was down to just 50,000, despite the population increasing drastically in much of Western Europe.
As humans, we now seem to live in numbers far beyond our carrying capacity as well. This should not come as a shock, considering that there were only around seven million of us 10.000 years ago, rather than seven billion. The WWF calculates that we’re using the resources of 1.5 Earths to sustain ourselves.2 There are many resources we’re using more intensely than they are replenished. The most well known is perhaps the Earth’s ability to sequester CO2.
Everyone knows that we have to reduce our emissions. However, many people are too optimistic about the consequences. We’re forced to reduce our CO2 emissions far beneath levels our economy seems to require to function.3 If we want to have the whole world to live the lifestyle of Europeans by 2007, CO2 emissions per dollar of GDP would have to be reduced to 14 gram, from our current level of 768, before 2050.
What happened in Iceland is known as a state shift. The ecosystem moves from one stable state to another, but it’s practically impossible to move the ecosystem back to its previous state. A state shift can be compared to dropping a glass of wine on your table. It’s relatively easy to spill the wine, but practically impossible to get it back in.
A study published in Nature a few years ago looked at the issue of state shifts in global ecosystems. It concluded that what happens on a local level is now about to happen on a global level.3 The Earth is entering a new state. When this process is complete, it will be impossible for us to move back to the type of global ecosystem we inherited.
The enormous problem we face today is that our situation of ecological overshoot is reducing the long-term global carrying capacity of our species, as a result of the global state shift that is now in process.
One aspect of the global state shift is found in our habit of overfishing. The fish stock we have decimated are simply not capable of recovering, because their absence has changed the ecosystem in such a way that recovery is made impossible.4 The ocean will instead begin to resemble a bacterial soup, inhabited mostly by jellyfish, rather than bony fish.
Many species will actually go extinct in the coming decades, despite our best efforts to save them, simply because of an extinction debt that has already been built up. Their genetic diversity has become very low and as a result of their present low population, some alleles will be lost from their gene pool. In addition, some harmful alleles will become fixed in the gene pool. This is part of a process referred to as mutational meltdown, that makes a species incapable of recovery.
The potential risk of Rhinoceros extinction in Africa would dramatically change the ecosystem there as well. The Rhinoceros habit of preying on particular plants ensures a diversity of grassy plants in their landscape. Rhino-inhabited areas have 20-times more grazing lawns, places where species of grass grow that are prime nutrition for a variety of smaller grazing animals. Rhinos are thus a keystone species, without whom the whole ecosystem would fall apart.5
Even in the absence of any further deforestation and economic expansion, a whole list of extinctions will inevitably follow, simply from the damage that has already been done to our ecosystems. In the Amazon rainforest, only 20% of all extinctions of vertebrates as a result of deforestation that has already happened have occurred so far.6 The other 80% will happen in the future, simply because the animals have lost the forest that sustains them. In Hungary, there are currently seven more species of raptors surviving than the remaining forests can sustain.7
Rainforests can not survive without the animals that inhabit them, as bats and birds are responsible for distributing more than two thirds of the species of plants.9 The large animals threatened with extinction are also responsible for essential nutrient dispersal for plants.10
The libertarian suggestion of maintaining surviving biodiversity in parks funded through tourism is a pipe dream. Most species can’t be sustained under such conditions, they will go extinct. In addition, even most environmentalists, who aim for “sustainable growth”, or if they happen to be ambitious enough for “a zero-growth economy”, are nowhere near ambitious enough.
The effect that the whole situation will have on our long-term carrying capacity is not good. Our meat production is going to suffer drastically, as a third of the world’s fish catch is now used as animal feed. Besides thus delivering a third of animal protein indirectly, fish as a percentage of direct human protein intake amount to 8% of our total protein intake from all sources.8
Our ongoing emissions of carbon dioxide are also ensuring that the carrying capacity for our species in the future will be much lower than it is today. Our ability to practice agriculture will suffer drastically from the increase in weather extremes that forests are better able to cope with than fields of grain.
Like happens to every other large vertebrate that suffers overpopulation, the ecosystem we inhabit tries to reign us in. Malaria only becomes endemic in an area when non-human vertebrates that serve as dead end hosts for the parasite decline below a critical treshold.11
Unfortunately, nature has been unable to prevent our domination of the entire world and we have been unable to prevent it ourselves as well. The United Nations was recently forced to update its population projection for 2100. Instead of peaking in 2070 at nine billion, new estimates now show our population continuing to grow until 2100, to 11 billion.12 The main reason for the increase is a lack of decline in fertility rates in Africa, where 2 billion more people will live by 2100 than previously estimated.
In Europe, fertility rates are surging again as well. In the United Kingdom, immigration has ensured that fertility rates remain elevated, as immigrants have higher fertility rates.13 The UK and other European nations continue to allow immigrants into their nations, because these nations can not meet their financial obligations without a large demographic of young people.
Environmentalists who propose a zero economic growth economy are thus not proposing a realistic outcome, because the economies depend on growth to continue functioning, ensuring that their policies will never be accepted by policymakers.
Our economies can either grow or collapse, our politicians have decided to choose for growth. Depending on how long they manage to keep this growth going, the worst case scenario would see most of the Earth rendered uninhabitable to human life by 2300.15 Entire parts of China, India the United States and Africa would be so warm that humans can not even stay there for more than a few minutes without dropping dead.
If we want future generations to inherit a habitable planet however, our most realistic option is to do whatever it takes to provoke the collapse of our industrial economies. As a result of extinction debt, land presently under domination of humans has to be returned to nature for non-human species to survive. All indicators show that we are already in drastic overshoot, with species extinction rates now a thousand times higher than normal.14
As a result of the increasingly interdependent nature of every aspect of the modern economy, industrial collapse can be global and any attempt at reconstruction can be rendered impossible. It may appear as a gargantuan task, but this is the only real hope we have. The long-term survival of every species, including our own, depends on our overshoot being corrected sooner rather than later.
1 – http://www2.sunysuffolk.edu/mandias/lia/decline_of_vikings_iceland.html
2 – http://steadystate.org/wp-content/uploads/Jackson_2009_Beyond_the_Growth_Economy.pdf
3 – http://grist.org/climate-energy/were-about-to-push-the-earth-over-the-brink-new-study-finds/
4 – http://qz.com/166084/overfishing-doesnt-just-shrink-fish-populations-they-often-dont-recover-afterwards/
5 – http://www.smithsonianmag.com/articles/heres-what-might-happen-local-ecosystems-if-all-rhinos-disappear-180949896/?no-ist
6 – http://www.sciencemag.org/content/337/6091/228
7 – http://www.sciencedirect.com/science/article/pii/S1439179106000223
8 – http://www.greenfacts.org/en/fisheries/l-2/06-fish-consumption.htm
9 – http://www.griffith.edu.au/__data/assets/pdf_file/0011/297605/Seed-Disperser-Fact-Sheet_Moran_FINAL-April2011.pdf
10 – http://news.mongabay.com/2013/0812-hance-megafauna-amazon-nitrogen.html
11 – http://www.plosntds.org/article/info%3Adoi%2F10.1371%2Fjournal.pntd.0002139
12 – http://www.scientificamerican.com/article/world-population-will-soar-higher-than-predicted/
13 – http://online.wsj.com/articles/SB10001424127887323477604579000830777336474
14 – http://news.mongabay.com/2014/0529-hance-extinction-rates.html
15 – http://www.newscientist.com/blogs/shortsharpscience/2010/05/earth-2300-too-hot-for-humans.html