Those polls were taken during or soon after the media blitz which accompanied the release of the IPCC Working Group I Summary for Policy Makers, Al Gore's testimony to Congress and "An Inconvenient Truth" winning the Oscar.
Global warming couldn't keep up that kind of media saturation all summer. Nevertheless, a poll taken by Yale and Gallup in July showed a high level of awareness of the problem and what level of action might be needed. From Science Daily:
A growing number of Americans consider global warming an important threat that calls for drastic action, and 40% say that a presidential candidate's position on the issue will strongly influence how they vote....Sixty-two percent of respondents believe that life on earth will continue without major disruptions only if society takes immediate and drastic action to reduce global warming....A surprising 40 percent of respondents say a presidential candidate's position on global warming will be either extremely important (16 percent) or very important (24 percent) when casting their ballots.Annoyingly, this is not the same group from Yale that did the poll back in March. They didn't ask exactly the same questions.
The same group that did the July survey also adid one in September about local responses to global warming. The NYTimes covered it...it their blog.