Also thanks to Thoreau, we can understand point to specific examples that show just how freakishly warm this past winter was. In its wake, many plants flowered earlier than ever before, breaking records, said Primack.

For example, high bush blueberries flowered in mid-May in Thoreau’s time, he said. In recent years, early May or late April was the norm. That year, said Primack, the starting date was an astonishing April 1.

Pictured: Naturalist Peter Alden lead a group of Thoreau Society Members through Walden Woods in 2002.