Has Earth reached its carrying capacity?

­Carrying capacity is not a fixed number. Estimates put Earth's carrying capacity at anywhere between 2 billion and 40 billion people [source: McConeghy]. It varies with a wide range of factors, most of them fitting under the umbrella of "lifestyle." If humans were still in the hunter-gatherer mode, Earth would have reached its capacity at about 100 million people [source: ThinkQuest]. With humans producing food and living in high-rise buildings, that number increases significantly [source: ThinkQuest].

As of 2008, there were about 6.7 billion people living on this planet [source: Sachs]. A good way to understand the flexibility of Earth's carrying capacity is to look at the difference between the projected capacities of 2 billion and 40 billion. Essentially, we're working with the same level of resources with both of those numbers. So how can the estimates swing so widely?

Because people in different parts of the world are consuming different amounts of those resources. Basically, if everyone on Earth lived like a middle-class American, consuming roughly 3.3 times the subsistence level of food and about 250 times the subsistence level of clean water, the Earth could only support about 2 billion people [source: McConeghy]. On the other hand, if everyone on the planet consumed only what he or she needed, 40 billion would be a feasible number [source: McConeghy]. As it is, the people living in developed countries are consuming so much that the other approximate 75 percent of the population is left with barely what they need to get by [source: McConeghy].

To the surprise of those scientists who dismissed Malthus' prediction as fatally flawed, this limit on resources appears to stand despite the human ability to develop technologies that alter Malthus' presumed linear growth of the food supply. The issue, then, is why technology isn't saving us from the disaster of naturally mediated population control.

What are we doing wrong?

­If we look at the va­st advances in food-production technology, known as the green revolution, we would expect to be able to feed everyone on Earth indefinitely. The more people there are, the more inventors and advances in irrigation, agriculture, genetic engineering, pest control, water purification and other methods of increasing the food and water supply beyond what our habitat would provide normally. But in fact, food prices are rising at an alarming rate. The problem, it seems, has to do with the uniquely human byproducts of technological advancement, like systematic habitat destruction. We appear to be using technology in a way that defeats the purpose.

The ideal use of technology -- the use that would extend Earth's carrying capacity -- is to find ways to make fewer resources stretch much farther. Take, for instance, the Earth's energy resources. Ideally, we would've switched en masse to technologies like solar power and electric cars long ago. Instead, we've used technology to simply extract and use more fossil fuels. So instead of technology allowing us to live better on less, we're living better on more.

Since oil is a limited resource, and our technologies like home heating systems and farm equipment still run primarily on oil-dependent power, when we run out of oil, we potentially freeze to death in winter and run out of food. At the same time, air and water pollution resulting from technological advancement is reducing our supply of even more necessary resources.

So, are we doomed? Not if we make lifestyle adjustments that get us back into balance with our habitat. Major worldwide shifts to sustainable energy resources like sun and wind, and a movement toward eating locally grown food, reducing carbon emissions and even taking shorter showers can help. Mining space for additional resources might also help us avoid Earth-wide shortages, although that's a far more uncertain solution to the problem [source: ThinkQuest].

Ultimately, the idea is this: If everyone on Earth can manage to do more with less, we'll be back on track to Earth's indefinite carrying capacity. Also, since economic development and education tends to lower fertility rates, spreading modern knowledge to currently under-developed parts of the world can work as a sort of natural population control, further extending the lifetime of humanity on Earth [source: The Economist].

For more information on carrying capacity and related topics, look over the links on the next page.