Henry David Thoreau, as it turned out, was probably the first phenologist. Phenology is the study of timings in the natural world, eg, when trees bllom, when birds have their eggs timed to insects emerging and so forth. Thoreau kept meticulous detailed noted on such things, noting not only temperatures and when events took place, but noting the dates they did. This gave scientists over a century later an excellent baseline data set to assess how the natural world is responding as the planet warms.