Freakonomics was a highly popular book that appealed to both liberals and conservatives. Therefore, it carefully avoided polarizing topics, and instead uncovered the shocking truth about sumo wrestlers and other issues that are worthy of a standard 20/20 television show. Fun stuff, not what I would call economics (see the more esteemed economist Ariel Rubinstein for support).
So, this time they figured they would slay some fallacies in the Global Warming debate. They bend over backward to apply good faith to Global Warming proponents, and agree with many of it's propositions(it is not a singular hypothesis), yet try to have fun with some issues that appear ripe for debunking (eg, noting that horses generate more pollution than oil as an energy source). Unfortunately, the Global Warming Community does not approve of their shenanigans. They have too start action, now, and these issues hurt the cause. Levitt seems to like being against conventional wisdom only on areas where there are very few opinions, so he and his coauthor weaken their case by protesting too much, trying to have it both ways (I love the Weitzman argument that since a catastrophe could happen, we should spend trillions of dollars on it--it can be applied to anything, and indeed, he has used it to explain the equity premium puzzle).
Unfortunately, alternative energy sources that are currently most viable, like cleaner coal, or nuclear, are not popular with the Global Warming crowd. Even windmills, and solar, are coming into opposition for their noise or eye pollution. The only thing they really like are pie-in-the-sky battery research, and conservation. I think this highlights that most of this debate is not about Global Warming, but more power to regulate, because it adds another busy body to approve all sorts of things (like when I have to get permission from my city when I replace my old back patio with a new one).
The Global Warming debate is like many Big Issues. They are multifaceted, so debunking a point hardly makes a difference because most people's opinion has several several pillars. Given it will take my lifetime to provide any conclusive data one way or another, I don't expect this one to subside.