You can't say that with complete certainty.
To blithely suggest that human activities have zero impact on the surrounding environment is just as idiotic as saying that their impact dwarfs that of natural physical processes. I can be certain that humanity does have an impact on its surrounding environment, however, I believe that humanity, on the whole, has a super-sized ego and a penchant for arrogance...that's been around for a long time, in its attempts and desire to control the weather.
The bottom line here is that yes, human activities do influence the environment, but no, I don't think humans are sufficiently sophisticated to accidentally terraform an entire planet in just over two centuries. Now, if Sanford is arguing that the Government ought to protect the common, shared environment, just as New England towns once maintained their village greens as public property, by promoting such ideals as energy efficiency and conservation in the actions of Government with respect to public property, then yes, I wholeheartedly agree with him. The Government has a duty and obligation to the citizenry to not act in a wasteful manner. However, if he is promoting energy rationing and Government interference in the lives of individuals, e.g., through carbon cap-and-trade, then no, I won't support him.