The UCS mailed out over 1600 survey forms to climate scientists and based their assertions of political interference on the 297 that got returned. That's a response rate of just 19 percent. OMB guidelines clearly state that a response rate of less than 80 percent requires an investigation of potential biases and an even closer investigation for a response rate lower than 70 percent. A response rate of lower than twenty percent is clearly vulnerable to the charge of a self-selecting sample, perhaps those with an axe to grind against their bosses, the politically motivated, and so on. In short, it proivides all sorts of legitimate reasons to dismiss the survey as utterly unrepresentative.
I will say it again: The UCS found over 100 government climate scientists claiming political interference with their work or the dissemination of that work. It is beyond perverse to attack this finding on the grounds that it isn't "representative"--that's not the point. Suppose the UCS had never even called this a "survey" at all but just announced numbers of scientists reporting political interference. They would still have documented a very disturbing phenomenon. Or alternatively, imagine that the survey was representative after all, but only 10 percent of scientists reported political interference. That would still be a serious problem. These considerations show that the "unrepresentative sample" argument, although perhaps the best the right can do, is utterly vacuous.