From Envirowiki

Population is the number of organism from a single species with a given characteristic, usually a geographic area, but also physical features or behavioural patterns, such as culture.

[edit] 1 Over-population and sustainable population

Over-population occurs when the individuals of a species are so numerous that they can no longer be supported by its environment. This intersects with competitor population, in that if two competing species becomes too populous, food sources will become scarce.

A sustainable level of population is one in which population is fairly stable, and there is no net decrease is resources, such as food, that that population relies upon.

[edit] 2 Human population

Human population, when considered with individual environmental impact, effects how much the human species damages the environment. This is expressed by the I=PAT formula. A greater population with a lower individual impact may have the same total impact as a smaller population with a greater individual impact. This can be seen in the real world with historical carbon emissions - Richer, less populous countries are vastly more responsible for greenhouse gas emissions since the industrial revolution than their poorer, more populous majority world counterparts. This is mostly due to the massive lifestyle impact of the minority world.

Human population is currently over 6.5 billion people, and is expected to reach 7 billion within the next few years. Even without the increase in population likely over the next decades, current population, combined with our current lifestyle is not sustainable. There are two ways to make it more sustainable: reduce population, or reduce consumption.

If the current population lived like the poorest people in the world, then the current population might be able to be sustained, however, this is a very hard way to live. The other option is to decrease world population. Many population campaigners campaign to decrease population growth rates in the majority world, but it logically makes more sense to decrease them in the rich minority world, where an average life has an impact orders of magnitude higher than an average life in a poorer nation.

In reality, both sides of the population equation should be acted on - and immediate decrease in the waste and impact in the first world, and attempts to ethically reduce population growth rates all over the world (ideally to below 0, the rate of replacement, at least for a while).