Even giving him the benifit of the doubt and saying that he meant temperature changes: Well, he's wrong. Mars hasn't seen the same temperature changes. Assuming that he simply was speaking about solar output in broad terms, he's still wrong, since solar contribution to earth's temperature hasn't changed significantly or consistently.
So instead, let's assume the most optimistic interpretation of what he was trying to say: "Observed global warming is not due to human action." Well, he's still wrong, and strongly wrong. This isn't like string theory or something, we know all of the following facts about as well as we know anything about chemistry or physics, and we've known them for a hundred years or more... First and foremost, temperatures are increasing. Second, this temperature increase is correlated with CO2 increase. Third, Co2, and other greenhouse gasses, have a clear mechanism for increasing temperatures. Fourth, human activity is releasing geophysically significant quantities of (read: LOTS OF) CO2. Fifth, this CO2 remains in the atmosphere (we know because we can actually tell what CO2 came from oil and what came from trees, the ocean, etc.)
Let's go nuts. Let's say that he has secret information that says that it's not human activity. Maybe climate change skeptics know about some secret Obama plot to cover up millions of natural volcanic eruptions happening all of the time all over the planet, or something like that, and that at the same time, a massive scientific conspiracy has spread the total lie that coal and oil release CO2, when in fact combustion is how butterflies are born.
IF THAT WAS THE CASE: Who cares? We know the climate is changing, Senator Smith said the climate was changing. Are we just going to let this "natural" change raise sea levels, destroy farmlands, and cause untold loss of rare and unique life forms on earth? Sure, sooner or later change is going to happen, but human beings do quite a lot of work to control natural change as it is. So, unless you want to shrug your shoulders at Hurricane Sandy and say "Well, who wants subways anyway, they'll flood eventually," and "Why should I maintain the roads? Sooner or later, they'll get potholes..." you've got to address climate change somehow. Saying it isn't man-made is the smallest, stupidest, least important part of the problem, and it hints at a deeply nihilistic viewpoint.