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What Happens When the Earth Is Full?


The photo at the right, shot from Apollo 11 as the Earth rose over the moon, reminds us of how beautiful the Earth is.  It also reminds us, that though the Earth seems large to us, our space is limited and our resources are finite. What will happen when the Earth is full?
 The human population just reached the milestone of 7 billion people. Our population has been growing at the rate of about 2% each year which means that the population will double about every 35 to 40 years. If we do not reduce our birthrate or experienced some great catastrophe, the population will reach 14 billion by 2050 and 28 billion by 2090. It is rather hard to imagine what the Earth would be like with that many people and is almost assured that that will not happen. Estimates are that the number of people who can live comfortably on the Earth is around 9 billion. That estimate may be off a few billion if you include advances in food production and measures to reduce our rate of pollution. However, it should be clear that at some point the human population will grow larger than the Earth’s ability to support it. The graph in the article Limits to Growth and Beyond, Part 1, shows that may happen within the next generation. What will happen then?
That has never happened before to the human population, but there are examples in nature where population is limited to a small area, such as bacteria in petri dish. When the nutrients are gone, so are the bacteria. There are a few examples of mammalian populations where the species is confined to a small area and the natural predators are eliminated, such as a Moose population established on Isle Royale in Michigan, where there were no wolves.  The moose population grew rapidly until almost all the vegetation on the island was depleted and then the moose population declined dramatically due to starvation and disease. One of the best examples is this case study of the deer population on the Kaibab Peninsula in northern Arizona.

In 1907 the deer population was unusually low with only 4,000 head. The carrying capacity was 30,000 at this time, so a massive campaign was waged against the natural enemies of the deer. Between the years of 1907 and 1923, the natural predators of deer (mountain lions, wolves and coyotes) were eliminated by hunters in order to increase the deer population. As the following graph shows rather dramatically, the deer population increased rapidly to 100,000 by 1924, but then died off rapidly to a mere 10,000 by 1939. Because of severe overgrazing by excessive populations of deer, the carrying capacity of this region was reduced to approximately 10,000 in 1939, and the deer population was reduced accordingly.


Deer Population on the Kaibab Plateau

The graph at the right shows what happened to the deer population during this period. When the carrying capacity of the environment is exceeded, natural populations do not reach an equilibrium point and stay there.The result is a massive die off, and the population is decreased below their original carrying capacity. The Earth has a carrying capacity for man, and though we are not exactly sure when we will reach it, it will undoubtedly be within this century. What will happen then?

(c) 2012 J.C. Moore

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4 Responses to “What Happens When the Earth Is Full?” »

  1. admin Says:

    Some people think the Earth is already full. There is a good video that discusses this topic at http://www.ted.com/talks/paul_gilding_the_earth_is_full.html.

  2. John "Ratty" Arbuckle Says:

    Balderdash! We are not animals. We have science, technology, and human ingenuity. Plus birth rates are falling all over the world. Most likely we will never reach a carrying capacity for humans. There is probably NO carrying capacity for a species like man. In the 1970s, the carrying capacity for humans was estimated to be 5 billion. Then 6, then 7, now 10. It will keep increasing as our tech continues to increase. Relax.

  3. J.C. Moore Says:

    You may be right, but then again, what if you are wrong? When you factor in climate change, the carrying capacity of the Earth may began to decrease in ways that no technology can overcome.

  4. John "Ratty" Arbuckle Says:

    Oh right, “climate change”. *EYE ROLL*

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