loves the Earth.


How Many Crew for Spaceship Earth? Carrying capacity and unlimited growth

For those of you not familiar with the story of St. Matthew’s Island, a remote island in the Bering Sea off the coast of Alaska, allow me to recount the tale. It is a factual story and shines a light on animal behavior, including our own, in the face of seemingly unlimited resources.

St. Matthew’s Island

Natural and human history are full of examples in which animals or humans exceeded carrying capacity, or the maximum population size that the environment can support for ever. In other words, there is only a certain number of a species, like reindeer, humans, goats, etc, that a habitat can support given the food, water, and other necessities available, before resources are depleted and that species goes into decline, or extinction.

A haunting and oft-cited example of such an overshoot took place on St. Matthew’s Island in 1944. Twenty-nine reindeer were imported to the island as a backup food source for the 19 WWII soldiers that were manning a radio navigation system on the island. The reasoning was: in case boats with supplies couldn’t make it to the remote island on schedule, the soldiers could shoot off a couple reindeer for sustenance. Specialists had calculated that the island could support 13 to 18 reindeer per square mile, or a total population of between 1,600 and 2,300 animals.

St. Matthews Island, coincidentally, was a reindeer heaven–full of rich lichen and willow bushes that the reindeers feasted upon and they soon quickly reproduced. By 1957, just 13 years later, the population was 1,350 and the reindeer were healthy and fat from the carpets of lichen on the island.

Then, 6 years later, in 1963, with no natural controls or predators, the population had exploded to 6,000. The dense herd had dramatically thinned the layers of lichen on the island and their average weight had dropped. The lichen did not have enough time to regrow, but the reindeer kept multiplying and eating more lichen and willow bushes.

Just 3 years later, in 1966, a couple of researchers visited the island to see that, unfortunately, the original calculations had been correct. The 6,000 reindeer vastly exceeded the carrying capacity of the island and without enough food to support the larger population the reindeer were soon decimated by starvation and disease.

You would think that perhaps such a drastic overshoot might lead to a more stable population number, with the “extra” reindeer dying off. But no. Instead, the entire habitat was so damaged by the overpopulation and consequent overgrazing that the number of reindeer fell dramatically below the original carrying capacity. By 1966, there were only 42 reindeer alive on St. Matthew’s Island.1

The Island of Earth

This story relays the seriousness of surpassing an environment’s carrying capacity for a specific species. And what about the biggest island we inhabit, that of planet Earth? What is its carrying capacity for us humans?

In response to these questions, in 1972 a seminal piece of work came out entitled Limits to Growth. The book was written by a group of people from MIT who had created the first computer model to explore how exponential growth, such as human population growth, interacts with limited resources. The model tracked the trajectory of five variables, namely world population, industrialization, pollution, food production and resource depletion.

The model didn’t try to make specific predictions, since the exact size of resources was unknown, but explored the general behavior of growth on a limited world. Two of the final scenarios the model came up with saw “overshoot and collapse” of the global system by the mid to latter part of the 21st century, while a third scenario resulted in a “stabilized world.”2Looking back thirty years from when the book was published, you can see that their predictions were not 100% accurate, but are very close.

Image courtesy of Institute for Population Studies

Image courtesy of Institute for Population Studies

So, what does this mean? Mostly, the chart suggests that our current trajectories must be severely re-routed in order to avoid an economic and population collapse around the 2030s. And by rerouting, that means a change in behavior in how we use our resources, understand human capital and services, dispel waste, and populate.

Capacity for Climate Change

This 2030s capacity prediction also closely aligns with current climate change projections. For example, global surface temperature is expected to rise at least 2 degrees F by the late 2020s or early 2030s, which would completely melt the Arctic and Antarctic poles.3

This heat could even start thawing the permafrost that encircles the poles, which is currently trapping many gigatons of carbon. If the permafrost melts, which could happen as early as 2020, that trapped carbon will be released into the atmosphere and cause the planet to heat up even more.4

What is even scarier are the presence of trapped methane hydrates, or pockets of underwater methane gas that are currently encased in ice. If the polar waters warm too much and the ice melts, it could release 2500% more methane that is currently found in the atmosphere today.5And just to get that into perspective, a molecule of methane has 21 times the ability to trap heat in the atmosphere as one molecule of carbon dioxide. So yes, very hot, very scary.

How to Manage

Before you get too worried, realize that we are making strides (if slowly) to hopefully remedy some of the more devastating impacts of climate change. For example, after a long and strenuous political battle, a new amendment to the Farm Bill has emerged that actually awards subsidies for when farmers conserve their lands, such as wetlands, grasslands and erodable land.6 For decades, governmental subsidies based on crop production have caused farmers to use toxic fertilizers and pesticides to improve the yield of the crops, which over time has polluted the land and eroded the soil. It’s about time payment was given for preserving the land, an important carbon sink, instead of destroying it.

So, farmers are shaping up, but so are companies. Recently, the trend of incorporating ESG (environmental, social, and corporate governance) considerations into the overall rating of a company has spread across the financial world. Now, investors want to know a company is taking care of its waste, its employees, and its accounting books in a responsible manner that ensures less risk and more stable financial returns. The trend is building inertia with $5 trillion responsibly invested assets under management in 20117, with this amount projected to grow annually at a rate of about 25%, with the responsible investing market expected to total more than $25 trillion by 2015.8

Most recently, the EPA is crafting a brand new carbon bill to get the U.S. on track to limiting carbon emissions. The bill plans to cut carbon emissions from 1,500 power plants which are the largest source of America’s greenhouse gas pollution.9 The bill could be the most significant action taken by the United State to curb climate change, and could result in global leadership towards dealing with the climate crisis.

Although the facts are ominous, there’s still hope and all the more reason to do what we can to ensure our longevity on this beautiful planet. The more people who realize what a big challenge we have on our hands in terms of climate change and our consumption of natural resources and natural capital, the earlier we can start living like humans, and not end up like those reindeer.


1. Hawken, P. (1994) The Ecology of Commerce.
2. Meadows, D. H., Meadows, D. L., Randers, J. & Behrens III, W. W. (1972)The Limits to Growth.
3. Intergovernmental Panel on Climate Change (IPCC). (2013).Climate Change 2013: The Physical Science Basis.
4. Schafer, K., Zhang, T., Bruhwiler, L. & Barrett, A. P. (2011), Amount and timing of permafrost carbon release in response to climate warming. Tellus B, 63: 165–180.
5. Shakhova, N., Semiletov, I. & Panteleev G. (2005), The distribution of methane on the Siberian Arctic shelves: Implications for the marine methane cycle, Geophys. Res. Lett., 32, L09601
6. Sustainable Business News. (2014). Farm Bill aims to grow green power, hemp and organics.
7. Campden Research. (2011). Responsible Investment in Asia Research Report.
8. Business for Social Responsibility (BSR). (2012).Trends in ESG Integration in Investments.
9. Davenport, C. (2014). E.P.A. Staff Struggling to Create Pollution Rule.