The National Bureau of Economic Research is out with two studies illuminating effects that you might call unintended consequences.
The first, by Grant Jacobsen of the University of Oregon, Matthew Kotchen of Yale, and Michael Vandenbergh of Vanderbilt, looked at "billing data for participants and nonparticipants in a green-electricity program in Memphis, Tennessee." Some participants started using more energy once they had opted into the "green" program. If you think that electricity is coming from wind or solar power, you might as well leave on all those lights and turn on the air conditioner full blast, because you can still feel virtuous even while you are wasting the energy.
The second, by Sara Markowitz of Emory, found that "laws regulating indoor smoking are associated with increases in some types of fires. Specifically, workplace restrictions and bans are associated with increases in fires in all locations and in residential units. Restaurant and bar bans are associated with increases in fires in restaurants and all eating/drinking establishments." If smoking is illegal, there are no ashtrays, which means the butts instead get tossed in places they can start fires.