The story that the human global population will hit 7 billion by 2012 (6/20, A-1) only hints at the predicament we are in. The population has mushroomed since the start of the industrial revolution, when humans began consuming fossil fuels at a furious rate.
Humans in 2008 are super-sized in comparison with their pre-industrial ancestors. Annual human energy consumption has been estimated to be about 13 trillion watts. Divide by a world population of 6.7 billion, and you come up with an average human energy diet of about 2,000 watts-per-person annually. Since a 2,000-calorie-per-day human would use 100 watts of energy annually, each one of us is the equivalent of 20 hunter-gatherers. This suggests that if humans were energy-equivalent over time, the current global population is actually 130 billion.
Human reliance on dead organisms that lived millions of years ago (fossil fuels) is an example of a detritus ecosystem. There are many other examples of detritus ecosystems in nature, and they exhibit a cycle of bloom-and-crash. Like algae in a pond, which flourishes in the spring on the organic remains from the previous fall, humans can probably expect a crash after the current population bloom.