My biggest gripe when it comes to CO2 release (whether or not you figure it is causing the observed climate change) is automotive aerodynamics.
Before my current job i was in the auto industry, being involved in various aspects of development for many vehicles. It never ceases to amaze me how unimportant aerodynamics was considered next to styling. The body guys did all they could to keep weight down, while meeting NCAP crash specs. The engines guys did their level best to minimise BSFC fuel burn. There was even some work done on hybrids. Aerodynamics was only ever given a cursory once over.
Citroen produced a car many years ago with a Cd of 0.19 - hence the name DS19. For comparison the proverbial brick has a Cd of 1.0, and a helicopter fuselage has a Cd of ~0.1. If CO2 is a major concern why am i driving a car which is wasting twice as much fuel as it could be churning up the air? There are many many more cars than helicopters...
Rant over.
Comment about nuclear powerd helicopters was tongue in cheek, but it was once seriously considered for very long range bombers...
http://en.wikipedia.org/wiki/Nuclear_aircraft