However, this birthday isn't something to celebrate.
Since the global population passed 6 billion only in late 1999, we've added more than 80 million people each year on average. And the environmental footprint of those people is expanding rapidly as emerging market populations modernize.
The planet may be able to accommodate these extra people and their consumption - but then again, it may not.
And if it can't, the drain on our planet's resources could harm us all.
So we'd better find a way to reduce population growth - fast.
Of course, if you think I'm about to propose something along the lines of China's one-child policy, you couldn't be more wrong.
We have economic means of population control that are neither coercive nor costly. And the sooner we implement them, the better.
A Disaster in the MakingWhen Thomas Malthus warned of overpopulation in 1798, the global population was approaching 1 billion - a level it reached in 1804. It had grown in the previous three centuries from 500 million in 1500. Thus, if the gradually increasing prosperity of 1500-1800 had continued - without the Industrial Revolution increasing world production capacity artificially - it would have reached 1.62 billion by 2011.
There is a very good case to be made that 1.62 billion is today's natural population, and that the growth since 1800 is artificial, caused by the Industrial Revolution removing previous limits on production. At that level, almost all serious environmental problems would go away. Even if all 1.62 billion of the world's inhabitants enjoyed Western living standards, the global warming and pollution effects of their output would be easily absorbed by the planetary ecosphere.
Around 2004, U.N. population projections had us reaching a population of 8 billion by 2027, then peaking at around 9.3 billion just before 2050 and declining slowly thereafter. Alas, the latest projections are not so sanguine. They have no peak in population this side of 2100, with population passing 10 billion and reaching 10.12 billion in 2100.
At this level, an environmental disaster is very likely.