California Democratic Sen. Barbara Boxer presides over an Environment and Public Works Committee considered about as partisan as a panel can get. Ideological differences among the committee's Democrats and Republicans are evident every time the panel meets, creating a political dynamic that raises big questions about the fate of climate change legislation that Boxer and Sen. John Kerry (D-Mass.) plan to unveil tomorrow. Historically, the EPW Committee is known for its bipartisan accomplishments, including the Clean Air Act and Clean Water Act. But experts agree that the committee's upcoming and far-reaching effort on global warming will take place in a much different political atmosphere.