By fact-checking Thoreau's observations at Walden Pond, we showed how old diaries and specimens can inform modern research

Scientists have used author Henry David Thoreau's notes to inform studies of climate change in eastern Massachusetts. Tom Stohlman/Flickr, CC BY-SA

Henry David Thoreau, the environmental philosopher and author of “Walden”, was a keen observer of seasonal change. In 1862, for example, he wrote in the Atlantic Monthly:

“October is the month of painted leaves. Their rich glow now flashes round the world. As fruits and leaves and the day itself acquire a bright tint just before they fall, so the year near its setting. October is its sunset sky; November the later twilight.”