Which do you believe is the biggest immediate threat to mankind?

[tecoyah]

OK...the rainforest is a self regulating system for the most part, and manges to create local weather through its very existance. The point is there is very little correlation between the weather in a rainforest and Global Climate, thus the term "Global". At issue here is not whether madagascar gets a bit drier, or Hawaii sees a drought for a couple years, but rather a change in the mean temperature of this entire planet, and the implications this will have on Human comfort levels.
We all have a stake in the results of this seemingly "Real" effect taking place during our lifetimes, and some are likely to be adversly affected by the change, while others will benefit. I have decided this is the "Biggest Immediate Threat to Humankind" based on the likely impact felt by everyone who meets the definition of Human.

 

[Trajan Octavian Titus]

A nuclear Iran. Can you say nuclear winter and armageddon? I knew that you could.

 

[The Real McCoy]

Biggest immediate threat? Radicals with CBRN weapons.