Here is a nice little doomsday scenario for all the left-wing tree-hugging, environmental do-rights out there who believe that man-induced global warming is real.
Lets convert all vehicle propulsion to renewable sources - like ethanol, and all buildings to solar and wind powered climate control.
Then lets have a nice famine and/or massive crop failure.
This could be caused by a big volcanic explosion like Mount Saint Helens.
Or from drought similar to the climatic cycle the affected the mid-western United States in the 1930's.
Or a nice big comet or meteor landing.
I am not talking about a huge movie-sized catastrophe, but big enough to throw some dirt in the air for a year or two.
Like Mount Krakatoa did in 1883.
Then lets watch the world economic system come grinding to a halt.
Then lets see what the eco-nazis have to say about their "perfect" little world that they fought so hard to establish with their fairy-science (as in, fairy tales).
We can all go over to Al Gore's house to keep warm (or cool).
Maybe he can invent some natural gas to keep us comfortable.
He already invented natural gas.
He passes it out when he talks.