A good post at The New Yorker, summarizing the growth of human population. Earth should hit the 7,000,000,000 population mark sometime in the next two to three weeks:

Sometime on October 31st, the world’s population will hit seven billion. The baby who does the trick will most likely appear in India, where the number of births per minute—fifty-one—is higher than in any other nation. But he or she could also be born in China—the world’s most populous country—or in a fast-growing nation like Nigeria or Guatemala or, really, anywhere. The idea that a particular child will on a particular day bring the global population to a particular number is, of course, a fiction; nobody can say, within tens of millions, how many people there are on earth at any given time. The United Nations Population Fund has picked October 31st as its best estimate. That this date is Halloween is presumably just a coincidence…

If you aren’t already familiar with Thomas Malthus’s famous treatise, An Essay on the Principle of Population, in which he espouses that the rate of human growth will outstrip the food supply (which he argued, grows linearly), you should take a look at this Wikipedia page. Malthus’s essay is mentioned prominently in The New Yorker piece.

Furthermore, making predictions is hard. Hence, the frequent revisions:

The further ahead you look, the trickier things become. This is partly a matter of birth rates; because the base is now so large, even relatively trivial changes produce enormous effects. In most European nations, and also in countries like Japan and China, birth rates have already fallen below replacement levels. Until quite recently, the U.N. was projecting that rates in other parts of the globe would follow a similar downward slope, so that sometime toward 2050 global population would level out at around nine billion. A few months ago, though, the U.N. announced that it was revising its long-term forecast. The agency now estimates that the number of people on earth in 2100 will be ten billion and still climbing. One reason for the upward revision is that birth rates in many developing countries, particularly in Africa, have remained unexpectedly high.

The big question: is there a theoretical asymptote for the number of humans that Earth can sustain? If so, what is that number, to a first-degree approximation?