Yes global warming is happening.  Yes we need to do something.  But how much of something is up to debate.  From the NYTimes:

Dr. Pielke, a professor in the environmental studies program at the University of Colorado, is the author of “The Honest Broker,” a book arguing that most scientists are fundamentally mistaken about their role in political debates. As a result, he says, they’re jeopardizing their credibility while impeding solutions to problems like global warming.

Most researchers, Dr. Pielke writes, like to think of themselves in one of two roles: as a pure researcher who remains aloof from messy politics, or an impartial arbiter offering expert answers to politicians’ questions. Either way, they believe their research can point the way to correct public policies, and sometimes it does — when the science is clear and people’s values aren’t in conflict.

But climate change, like most political issues, isn’t so simple. While most scientists agree that anthropogenic global warming is a threat, they’re not certain about its scale or its timing or its precise consequences (like the condition of California’s water supply in 2090). And while most members of the public want to avoid future harm from climate change, they have conflicting values about which sacrifices are worthwhile today.