Author Paul Ehrlich devised the famous equation for evaluating human impact on the environment as a function of three variables: (1) population, (2) affluence, and (3) technology (UWBR, 2004). Much more recently, William Rees, of the Fisheries

Center at the University of British Columbia introduced a method for quantifying the specific natural resource demand represented by each person, expressing the results as an ecological "footprint" (UWBR, 2004). Combined with the fact that by the turn of the 21st

Century, the global human population reached 6 billion, the implications for the future of the planetary ecological systems and biosphere are extremely ominous to say the least.

According to experts like Rees, developed countries like the United States and Canada already account for an extremely disproportionate (collective) ecological footprint, to the extent that the entire natural capacity of the Earth would already be exceeded by 20% were all its inhabitants consuming its resources at the rate of North Americans (UWBR, 2004). Furthermore, the mere rate of resource consumption represents only a relatively small part of the overall equation. Human industrial activity contributes to the depletion, destruction, erosion, and other dramatic changes to the ecological environment that are detrimental to nonhuman species whose continued health depends on ecological balance, as well as to future generations of human beings who will depend on its resources as well.

Already, we are...

In the last century, human consumption of fossil fuels is far outpacing sustainable capacity, but its depletion represents only the tip of the iceberg in terms of the future of this planet. Many experts firmly believe that human activity is the main cause of global warming, whose myriad effects include everything from the endangerment of animal species in habitats that supported them for thousands of years to weather changes that may reshape coastlines worldwide and even threaten the future existence of entire continents themselves.
References

Castilla, J.C. (1999) Coastal Marine Communities: Trends and Perspectives from Human-Exclusion Experiments. Retrieved, November 2, 2007, at http://66.102.1.104/scholar?hl=en&lr=&safe=off&q=cache:ed1L7vUsG7sJ:ib.berkeley.edu/labs/power/classes/IB250/Castilla_1999.pdf+human+population+growt h+community+interaction+ecology

Clean Water Action Council of Northeast Wisconsin, Inc. Population Growth: Impacts on the Environment. (2007) Retrieved, November 2, 2007, at http://www.cwac.net/population/index.html

University of Wisconsin Board of Regents (2004) Assessing Immigration, Population & Environment. Retrieved, November 2, 2007, at http://whyfiles.org/200immigration_pop/2.html