Sen. Barbara Boxer had been chair of the Senate's Environment Committee for less than a month when the verdict landed last February. "Warming of the climate system is unequivocal," concluded a report by 600 scientists from governments, academia, green groups and businesses in 40 countries. Worse, there was now at least a 90 percent likelihood that the release of greenhouse gases from the burning of fossil fuels is causing longer droughts, more flood-causing downpours and worse heat waves, way up from earlier studies. Those who doubt the reality of human-caused climate change have spent decades disputing that. But Boxer figured that with "the overwhelming science out there, the deniers' days were numbered." As she left a meeting with the head of the international climate panel, however, a staffer had some news for her. A conservative think tank long funded by ExxonMobil, she told Boxer, had offered scientists $10,000 to write articles undercutting the new report and the computer-based climate models it is based on. "I realized," says Boxer, "there was a movement behind this that just wasn't giving up."