With an unstoppable global warming, overpopulation, and food and water shortages.

[Binkie The Clown]

131. Or maybe even a few thousand, or a few hundred thousand.

If not extinction now, at least the worst bottleneck in human history. Extinction awaits eventually, however.

But tens of millions of survivors? I seriously doubt it.

Climate change will push refugees north, causing crowding, conflict, violence, mayhem, possibly nuclear war as all of Africa streams into Europe and all of the equatorial Americans streams north into the northern U.S. and Canada.

As civilization falters under the load, and the electrical grid fails, nuclear reactors around the world, deprived of the power to keep them cool, will melt down. Spent rod pools will boil off and explode and burn and vast clouds of nuclear contaminants will spread across the globe. It's not a pretty picture, and I really wish it wasn't a near certainty, but the sad fact is, it's the most likely scenario for our immediate future.