On March 18, 2003, 20 years ago this month, Sen. Barbara Boxer (D-Calif.) stood on the Senate floor and showed her colleagues a picture of a polar bear. “Cast your eyes on this,” Boxer implored, gesturing toward the photograph behind her. A clear blue sky delineates the top of the image, while below a polar bear lumbers across the ice, its large white figure strikingly reflected in the water.