Excerpt from the 2005 book, The Weather Makers: How Man is Changing the Climate and What It Means for Life on Earth, by Tim Flannery:
“The twentieth century opened on a world that was home to little more than a billion people and closed on a world of 6 billion, and every one of those 6 billion is using on average four times as much energy as their forefathers did 100 years before. This helps account for the fact that the burning of fossil fuels has increased sixteenfold over that period…
“In 1961 there was still room to maneuver. In that seemingly distant age there were just 3 billion people and they were all using only half of the total resources that our global ecosystem could sustainably provide. A short twenty-five years later, in 1986, we had reached a watershed, for that year our population topped 5 billion, and such was our collective thirst for resources that we were using all of Earth’s sustainable production.
“In effect, 1986 marks the year that humans reached Earth’s carrying capacity, and ever since we have been running the equivalent of a deficit budget, which is sustained only by plundering our capital base. The plundering takes the form of overexploiting fisheries, overgrazing pasture until it becomes desert, destroying forests, and polluting our oceans and atmosphere, which in turn leads to the large number of environmental issues we face. In the end, though, the environmental budget is the only one that really counts.
“By 2001 humanity’s deficit had ballooned to 20%, and our population to over 6 billion. By 2050, when the population is expected to level out around 9 billion, the burden of human existence will be such that we will be using–if they can still be found–nearly two planets’ worth of resources. But for all the difficulty we’ll experience in finding those resources, it’s our waste–particularly the greenhouse gases–that is the limiting factor.”