As global average temperatures warm due to climate change, scientists have learned that plants are flowering earlier in the year than ever before.

More troubling, scientists explained this week in the journal PLOS ONE that Massachusetts and Wisconsin in particular saw the earliest flowerings in recorded history during 2010 and 2012: a clear sign that climate change is already having a very real effect on nature's annual cycle.

Using the writings of Henry David Thoreau and Aldo Leopold, two of America's most cherished environmental authors, scientists monitored dozens of different species of plant to determine how far off the flowering times would be compared to observations taken from 1852-1858 and from 1935-1945.

What they found is startling, yet simple: "Based on our linear regression analysis of these historical phenology and temperature data, plant species flower on average 3.2 days earlier for each 1°C rise in mean spring temperatures," they wrote.

Researchers added that 27 of the 32 species observed in Massachusetts are flowering much earlier than their historical norms, and the window for blooms has shifted along with the mean spring temperature. In Wisconsin, 23 of 23 species were observed flowering earlier than usual.

To test the theory that climate was driving early flowering, scientists went back and created a prediction model based on pre-2010 and 2012 data, finding that their forecasts were 95 percent accurate according to what actually happened during those years.

Researchers warned that while many species have tried to adapt to the changing climate, "at some point plants may no longer flower earlier in response to warming due to photoperiod constraints or unmet winter chilling requirements." That could leave a lot more vegetation ill-equipped to withstand droughts or other natural disasters driven by climate change.

"These results collectively demonstrate that despite record-breaking warm temperatures in the eastern United States, plants have continued to flower earlier in the face of recent dramatic climate change," researchers wrote. "While other studies have examined long-term observations with comparable rates of phenological advancement [...], to our knowledge ours is the first to demonstrate the predictive power of such data under unprecedented warm temperatures."