Sen. Barbara Boxer, D-Calif., left, gestures toward Sen. Joseph Lieberman, I-Conn., right, as he shakes hands with Sen. John Kerry, D-Mass. upon his arrival for a news conference on Capitol Hill in Washington, Monday, June 2, 2008, on the environment and global warming. (AP Photo/Susan Walsh)

Senate Environment and Public Works Committee Chairman Sen. Barbara Boxer, D-Calif., presides over a hearing on Capitol Hill in Washington, Thursday, Jan. 24, 2008, to discuss California's request for a greenhouse gas waiver. (AP Photo/Dennis Cook)

Senate Environment and Public Works Committee Chairman Sen. Barbara Boxer, D-Calif., holds tape which covered correspondence the committee received from the EPA during a hearing of the committee on Capitol Hill in Washington, Thursday, Jan. 24, 2008, to discuss California's request for a greenhouse gas waiver. (AP Photo/Dennis Cook)