Reply #8: There's no need for a cull. Circumstances are going to take care of our numbers.

[GliderGuider]

There are three sets of factors that seem likely to team up to affect our numbers over the next 50 years.

1. Climate change itself, shifts in rainfall patterns caused by climate change, soil depletion (from both fertility declines and erosion) and the depletion of irrigation water from the over-pumping of aquifers are going to interact to put a cap on overall global food production within 10 years.

2. Increasing energy costs - especially for the natural gas used to make fertilizers and for vehicle fuels refined from oil - are going to steadily increase the cost of both food production and delivery.

3. The global financial crisis that is now threatening Europe is going to spread like a pandemic through the rest of the world. As it does, it will undermine the entire global economy, with the vulnerable developing nations being hit first and hardest. Their ability to pay for increasingly expensive food imports and to keep life-sustaining infrastructure like medical care and public sanitation systems intact will be compromised. Money for humanitarian assistance will dry up just when it is needed most.

This convergence of factors points to a near-term peak in world population, with an outright decline beginning shortly afterward. It will not be caused by culling, though there will probably be some very unpleasant triage decisions made behind closed doors.

If I had to give numbers, I'd say that a peak of 8 billion around 2025 followed by a decline to under 4 billion by the end of the century seems probable.

That's the way I see it.