New York Times: Twenty years ago Monday, James E. Hansen, a climate scientist at NASA, shook Washington and the world by telling a sweating crowd at a Senate hearing during a stifling heat wave that he was "99 percent" certain that humans were already warming the climate. "The greenhouse effect has been detected, and it is changing our climate now," Dr. Hansen said then, referring to a recent string of warm years and the accumulating blanket of heat-trapping carbon dioxide and other gases emitted …