According to the UN, yesterday the planetary human population crossed the seven billion mark. The New York Times notes that there's some carping among the demographers as to the exact date but it hardly matters. There's a six month or so window of uncertainty, but we might as well pick a date to do a little collective reflection on the meaning of seven billion, and now will serve quite well.
The above shows estimates of global population from the time of Christ on: data are from the UN after 1950 and via Brad deLong before that. I like to look at it on this longer timescale as it makes it clear what an extraordinary event we are living through. The steepness of the wall in the second half of the twentieth century shows it graphically. Since I was born in 1965 the global population has more than doubled, and it could easily add as many people again before I die. It's an extraordinary thing for a population to have a doubling time markedly less than the lifetime of an individual member. Throughout the pre-industrial era the doubling time was many times longer than that, and indeed the population frequently shrank (for example, in the Dark Ages, and following the Black Death).
As to how it ends: who knows? Here is the range of official scenarios from the UN: