Rasmussen:

Just 22% of American adults followed news stories about the Live Earth concert Somewhat or Very Closely. That’s just one-fourth of the interest displayed in the recent Senate debate over immigration.
Most Americans (52%) believe the performers take part in such events because it is good for their image. Only 24% say the celebrities really believe in the cause.
Adding to the skepticism, an earlier survey found that just 24% of Americans consider Al Gore an expert on Global Warming. Public opinion is evenly divided as to the cause of Global Warming. Slightly under half (46%) believe that Global Warming is caused primarily by human activities. A roughly equal number believe warming is either the result of long-term planetary trends (35%) of some other cause (8%).