“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 making notes for a book on the seasons. Now, though, researchers at Boston University and Harvard are using those notes to discern patterns of plant abundance and decline in Concord — and by extension, New England — and to link those patterns to changing climate.”