More than a decade after investigations found that Exxon Mobil had known about the dangers of global warming since the 1970s but publicly downplayed the threat, lawsuits against oil companies have proliferated. There are nearly 40 of these cases pending across the country, according to Margaret Barry, who manages a climate litigation database at Columbia Law School’s Sabin Center. After years of delay tactics from the oil industry, at least five of these lawsuits — from Massachusetts, Vermont, Connecticut, the District of Columbia, and Honolulu — have proceeded to the discovery stage, in which both sides try to uncover evidence to bolster their case in court. That’s the last major step before a trial, when oil executives would be forced to defend their actions in front of a jury.