Researchers suggest this is evidence that plants are adapting to a changing climate.

They say records going back over 150 years indicate that wildflowers just keep blooming earlier as the climate gets warmer and warmer.

They found that for every degree of Fahrenheit the temperature increases, many flowers come out 2.3 days earlier.

Some of the data used in the study go back to observations left by the late Henry David Thoreau.

The famed naturalist and philosopher spent more than five years methodically collecting information on the dates of spring blooming around his beloved Walden Pond.

Thoreau was fascinated by natural history, and the pioneering contribution to climate monitoring begun in 1852 helps modern scientists judge the scope of global warming. 

“In 2010, plants flowered three weeks earlier than in Thoreau’s time and we thought we’d never see another year like that,” says Boston University biologist Richard Primack, who co-authored a paper on the findings in the journal PLOS ONE. “But then two years later, we had another record early flowering year both in Massachusetts and in Wisconsin.”

Flowering observations by environmental pioneer Aldo Leopold in Wisconsin, starting in 1935, were also used in the study.

Photo: Boston University