It’s the carrying capacity, stupid!
The Easter Island (Rapa Nui) is one of the most isolated inhabited islands in the world, being over 2,000 kilometers away from its closest neighbor the Pitcairn Island. By the time of European arrival in 1722, the island had no trees, a poor population of about 3,000 people, and a few hundred Moai statues that were scattered along the island’s coastline. The famous statues, each carved from a single massive stone, were puzzling to the European discoverers, as the islanders met by the Europeans seemed unable to support an artisan class, let alone move the monolithic statues of up to 86 tons. The mystery of the Moai statues invited some wild origin stories over the years, with some speculating that they were remnants from a civilization of the mythical sunk continent Atlantis, or even that they were extraterrestrial, but the most plausible version is told by James A. Brander and M. Scott Taylor: The statues were created before Easter Island civilization collapsed. Carbon dating of soil samples indicates that the first settlers arrived around 400 A.D. on an island that was covered with palm trees.1 The same technique shows a noticeable forest reduction from 900 A.D. and complete deforestation coinciding with the island’s population peak at 10,000 people around 1400 A.D.. Not long thereafter the island's first weapons appear in the archaeological records.
This grim history of the Easter Island can be explained with a theory that was introduced by Thomas Robert Malthus in 1798. In his “Essay on the Principle of Population”, Malthus warns for the dangers of population growth and resource consumption: “Population, when unchecked, increases in a geometrical ratio. Subsistence increases only in an arithmetical ratio. A slight acquaintance with numbers will shew the immensity of the first power in comparison of the second.”2 He describes that a population collapses if it outgrows the carrying capacity of its environment., the Malthusian catastrophe.
Malthus argues that there are two checks on the population size, one preventive check lowering the birth rates, and a positive check raising the death rates. Although Malthus’s work is best known for the Malthusian catastrophe, where a population collapses through higher death rates, Brander and Taylor point out that: “Malthus was not a fatalist. He believed that enlightened public policy could reduce population growth, contemplating both contraception and "moral restraint" as mitigating factors.”3 Malthus’s theory is said to have influenced both Charles Darwin and Alfred Russel Wallace, the pioneers of evolutionary biology, and has led the UK to keep census data through the British Census Act of 1800.
However, more recently, Malthus’s theory seems to have fallen from grace in mainstream economics.4 Critics of Malthus point out that the assumption of linear growth in food production is flawed and that the assumption that the population increases exponentially does not hold as countries get richer. Indeed, countries with high incomes have much lower birth rates, and during the last two centuries food production has grown faster than the population (although not without adverse effects, for example, claiming more land for agriculture and industrial fishing contribute to the loss of biodiversity). Some critics of Malthus go as far as to claim that we have not observed Malthusian catastrophes, obviously they are unaware of the textbook example of the Easter Island. I reckon that we would have observed more Malthusian catastrophes, if it wasn’t for migration.5
In explaining Malthus’s theory, I used the concept of the carrying capacity of an environment. Even though the term may not be attributed to Malthus directly, it is in line with the spirit of the theory.[iii] The notion that every environment has the ability to carry (or sustain) a population of a certain size implies that we face some level of absolute scarcity. You may wonder what the carrying capacity of our planet is, and several have tried to estimate it, but to me it seems that the carrying capacity can change over time.[iv] Economic development through technological progress can increase our carrying capacity, while economic growth through imprudent resource consumption, like the consumption of trees on the Easter Island, can deteriorate our carrying capacity.[v]
The notion that scarcity is absolute is at odds with how neoclassical economics treats scarcity. In neoclassical economics – the largest school of thought within economics today – resources are only scarce relative to one another. That is, one can substitute one scarce resource for another less scarce resource. This view on scarcity has led to many insights (some discussed in later chapters) and for long the assumption that only relative scarcity is relevant for economic activity seemed harmless, because it was inconceivable that human consumption could have global impact. However, it is becoming increasingly clear that we do have global impact. Recently, the scientific community started adopting the term Anthropocene to describe a new geological epoch during which human activity has a measurable impact on global natural processes.[vi] In the Anthropocene it has become harmful to ignore absolute scarcity. On top, ignoring absolute scarcity allows for the absurd idea that we can grow our economy forever.
Malthus’s ideas had a revival when Donella H. Meadows and her colleagues published a study called “Limits to growth” in 1972.[vii] This group, also going by the name ‘The club of Rome’, performed simulations of the consequences of exponential growth with finite resources. Their simulations included relations between the world population, food production, industrialization, resources depletion, and pollution. Their baseline – business-as-usual – scenario predicted that population overshoots the global carrying capacity and collapses in the second half of this decade or the next decade, unless we would take serious action on controlling our resource consumption. This prediction may come as a surprise, since we have never had higher average incomes and life expectancy. Still, a little over forty years later, we can assess how well their baseline scenario matches the data.
Source: Turner and Alexander (2014, The Guardian)
The ideas by Malthus as well as Limits to growth have received a lot of criticism. I want to highlight three critiques. First, the assumption of a linear progress of technology has been off for many technological developments so far: For example, the food production has increased faster than the population growth, although not only by productivity growth, also by claiming more land for agriculture. Another example illustrating the spectacular growth in technology is Moore’s law; that is, the number of transistors on an integrated circuit (read computing power) has doubled every two years. Second, the assumption that the population will increase if it can increase does not seem to hold as countries get richer. And third, the assumption that Earth has finite essential resources for which there are no substitutes is too strong for many resources. For example, renewable energy is becoming a viable alternative to fossil fuels.
Despite these critiques, I argue that we would do wise to take some of the lessons of Malthus and Limits to growth seriously. The concept that an environment has a carrying capacity to sustain a population of a certain size has been relevant on local scales in the past. Moreover, simply because we have not observed a Malthusian catastrophe on a global scale does not mean that it cannot occur.
First, there are examples that seem well in line with Malthusian catastrophes, where overpopulation damaged carrying capacity followed by a population collapse. Brander and Taylor (1998) take us to the Easter Island, a.k.a. Rapa Nui. The Easter Island is located 3,500 km away from the nearest continental point in Chile. The island is perhaps best known for its statues.
These statues posed been a bit of a mystery at the time of the European discovery in 1722. Upon discovery the island had no trees and poor inhabitants that could not have moved the statues, as they had neither the tools nor the knowledge to do so. The mystery of the statues has led to some exotic explanations, like that they dated from a sunken continent Atlantis or were put there by aliens, but the most plausible explanation sounds a lot like a Malthusian catastrophe. Carbon dating from Earth core samples indicates that the first settlers arrived on the island around 400 A.D. and that the island was covered by palm forest. The same techniques show a noticeable forest reduction around 900 A.D., and around the time that the population peaked at 10.000 in the 1400s the forests disappeared completely. Not long thereafter the islands’ first weapons enter in the archaeological records.
I speculate that the number of local Malthusian catastrophes would have been higher had it not been for migration, as evidenced by ghost towns where the local carrying capacity was seriously harmed. Moreover, I argue that the concept of carrying capacity is relevant at a global scale as well.4 Rockström et al. (2009) proposed planetary boundaries to human activity. These planetary boundaries can be seen as the most recent warning for a Malthusian catastrophe and seem the logical consequence of our arrival in the Anthropocene.
“I sincerely hope, for the sake of posterity, that they will be content to be stationary long before necessity compels them to it.”
John Stuart Mill (1857, Book IV p.?)
1. Brander and Taylor (1998) build on the archaeological work by Jo Anne Van Tilberg (1994) that describes the carbon dating results. See also Jared Diamond (2007).
2. Malthus (1798, p.4). Just in case the acquaintance with the numbers is present, but the acquaintance with the mathematical vocabulary is needed: A geometrical ratio gives exponential growth and an arithmetical ratio gives linear growth.
3. Brander and Taylor (1998, p.119-120)
4. For example, The Economist published “Malthus, the false prophet” in 2008 and Reuters blog ran an article entitled “7 billion reasons why Malthus was wrong” in 2011.
5. Coastal regions across the globe may see the carrying capacity of their environment eroded due to climate change, and we can expect many climate migrants unless these regions can adapt (for example, switch to floating homes and saline agriculture). For the Maldives, a country of almost four hundred thousand people and maximum elevation of 2 meters, floating cities may be the only possible adaption strategy as an alternative to migration.
6. Pierre-François Verhulst (1838) introduced the concept of a carrying capacity mathematically, while Nathan F. Sayre (2008) traced back the first use of the term to a report by the US Secretary of State in 1845.
7. In “How many people can the Earth support?” Cohen (1995) reviews estimates varying from below 1 billion to above 1.000 billion; the median of the upper bounds of 65 estimates is 12.
8. Daly (2013) recommends to distinguish between economic growth and economic development, where growth refers to an increase in the quantity of economic activity, and economic development refers to an increase in its quality. I intend to follow this recommendation.
9. Paul J. Crutzen (2002) introduced the term by referring to our impact on land use, the prevalence of river diversion, and the share of the fish stock used for human consumption, among other impacts. Colin Waters et al. (2016) add that the stratigraphic signature of humanity is sufficiently distinct to recognize this new geological epoch by reviewing evidence on the growth of new materials, such as concrete and plastics, and the transformation of land and ocean surface by mineral extraction and trawler fishing.
10. Another key contribution from the ’70s, Herman E. Daly (1974), is treated in a separate chapter, see Chapter ??
11. During the Copenhagen summit of 2009, the former Malidivian president Mohamed Nasheed argued for this boundary that gives an estimated 1.5 degrees Celsius global warming; see the 2011 documentary film The Island President. In 2015 Nasheed received a 13-year sentence under Maldives’ anti-terrorism act, Amnesty International called the conviction politically motivated. Free Nasheed!
12. Simon L. Lewis (2012, p. 417) points out some inconsistencies of the proposed planetary boundaries, among which: “Rockström’s published planetary boundary suggests that we could expand croplands by 400 million hectares before reaching the threshold — something that would seriously harm biodiversity.” According to fossil records, the pre-colonial value of biodiversity loss is between 0.1 and 1 extinctions per million species-years, while today the extinction rate is at least a hundred to a thousand times higher and it seems to be accelerating. Rockström et al. (2009) propose to respect a boundary of 10 extinctions per million species-years. While a boundary of 10 times the background extinction rate is an improvement to current conditions, I hope that you will succeed to bring back the extinction rate back to pre-colonial times.