The elephant in the room for energy is the Carbon Cycle. Burning plants isn't a big deal in affecting the carbon cycle over the long term (at least to first order) because it gets recycled from the air into the Earth over a few hundred years. (Ideally, of course, the burnt plants would be replaced by new ones to eat up the CO2 generated in the burning process. That's what biofuels is all about.) The problem with fossil fuels is that the stuff was locked up a long time ago, so the carbon cycle gets out of whack. The biosphere can't compensate for the huge disruption caused by large, quick changes, so the climate changes.
http://earthobservat...carbon_cycle4.php
IOW, burning biological stuff can be carbon neutral to the atmosphere over the medium term. Burning very old stuff that was brought up from deep underground isn't.
Cheers,
Scott.
(Who thinks that 200 years from now, people won't be burning stuff to get around, anyway.)