New York Times: Henry David Thoreau endorsed civil disobedience, opposed slavery and lived for two years in a hut in the woods here, an experience he described in ‘Walden.’ Now he turns out to have another line in his résumé: climate researcher. He did not realize it, of course. Thoreau died in 1862, when the industrial revolution was just beginning to pump climate-changing greenhouse gases into the atmosphere. In 1851, when he started recording when and where plants flowered in Concord, he was …