The House-passed climate change bill still faces many legislative hurdles with passage in the Senate seen as very difficult. Several climate change measures are being drafted in the upper chamber, where regional and philosophical differences are even more sharply defined.  Senate Agriculture Committee Chairman Tom Harkin (D-Iowa) said even with the support of President Obama, passage is “going to be very tough.” Sen. James Inhofffe (R-Okla.), the ranking member of the Environment and Public Works Committee that will hold a hearing on the bill, said the razor-thin passage in the House spells doom in the Senate. He called the bill “the largest tax increase in American history” and vowed a tough fight against the measure.  Sen. Barbara Boxer (D-Calif.), chairwoman of the Environment and Public Works Committee, plans a committee vote on climate change legislation before the August recess.