Fossil energy from oil, gas and coal may be the first limiting resource to disappear. The Cornell team cites research suggesting that world supplies of oil and gas should last about 35 years at current pumping rates, coal and uranium stocks about 100 years. The easiest natural resource to overlook is provided by the living organisms that share the planet with us. There are about half a million species of animals, plants, and microbes that provide essential functions for humans in the United States. Large-scale food production would be impossible without pollinators, decomposers, scavengers and waste recyclers.
Biodiversity also ensures a future gene bank for tomorrow's forestry and agriculture.
Researchers estimate that 150 species are lost daily due to human activity. In order to arrive at their optimum population figures, Pimentel and his colleagues make the optimistic assumption that humanity will make maximum use of Earth's finite resources. Even if humans make a transition to renewable energy sources, stop polluting and degrading their environment and accept a standard of living equal to one-half of that enjoyed by Americans today, the numbers stay the same. Getting there will be painful, Pimentel admits, but achievable. Population reduction will require a growing proportion of elderly to be supported by a shrinking number of younger, more productive humans.