I have not yet read the now-heavily criticized chapter 5 of Superfreakonomics, due for release tomorrow, and, no, I am not going to defend them. That some of their critics are wrong about something does not make them right, although this particular matter is one that depends on their exact wording, which I have not yet seen. It looks from all the comments that they are probably way off the deep end on many things, way overstating the benefits of geoengineering for resolving global warming (yes, we should have research on it as a possible emergency backstop down the road; no we should not dump other approaches to go with it), focus too much on questionable sources they do not even quote accurately, and say a lot of other dumb things, such as their claim that solar power worsens global warming because the panels are black (no, they are mostly blue and they do combat global warming, although because of their high cost, they will not likely do so much in the near future). Where their critics are wrong is when they characterize the views of climatologists in the 1970s as not at all supporting the hypothesis of global cooling, that this was just a view of a couple of oddballs and some media stories.
The strongest expression of this argument can be found on the blog by climatologist William Connolley at http://scienceblogs.com/stoat/2009/10/superfreakonomics_global_cooli.php. His argument is also picked at Real Climate and is based on a paper he did with Peterson and Fleck in the very respectable Bulletin of the American Meteorological Society about a year ago. available at http://ams.allenpress.com/archive/1520-0477/89/9/pdf/i1520-0477-89-9-1325.pdf (if I have gotten that right). It looked at the articles published in top climatology journals during 1965-1979, characterizing them as "pro-global warming," or "pro-global cooling" or "neutral," and concluded that only 12% of them (7) were "pro-cooling," leading to the dismissive commentary. However, this is misleading on various counts. The main one is that there was a period in the early 1970s when the count was not all that far apart. The facts were that there had been global cooling from the late 1930s that lasted well into the 1970s. Researchers were aware of this and aware of a competition between warming CO2 emissions and cooling aerosol/particulates emissions, although not sure about the relative strength of the effects. As time passed, things became clearer, and as of 1975, there were more pro-warming articles cumulatively than cooling-plus-neutral ones, with this balance then shifting more strongly that way afterwards, indeed with no "pro-cooling articles" after 1977. Of course, if Levitt and Dubner characterize the 1970s as a period dominated by a pro-cooling "consensus," then they are clearly wrong. But their critics on this point need to be more careful about how they state things, with many seriously mischaracterizing the situation then.