2 . Every spring, as the weather warms, trees up and down the East Coast explode in a display of bright green life as leaves fill their branches, and every fall, the same leaves provide one of nature’s great color displays of vivid yellow, orange and red.

Thanks to climate change, the timing of these events has shifted over the last two decades, Harvard scientists say.

Andrew Richardson, an associate professor of organismic and evolutionary biology, and research associate Trevor Keenan worked with colleagues from seven different institutions on a study which found that forests throughout the eastern United States are showing signs of spring growth dramatically earlier, and that the growing season in some areas extends further into the fall.

Richardson said, “Climate change isn’t just about warmer temperatures. It’s also about changes in precipitation (降水) patterns... so in the future, an earlier spring might not help forests take up more carbon dioxide if they end up running out of water in mid-summer.”

The research combined information from three sources. Using satellite data, Keenan tracked when forests across the region began to turn green in the spring, and when leaves began to turn yellow in the fall. Ground observations made every three to seven days at the Harvard Forest in Petersham and a long-term research site in New Hampshire provided information about the state of buds, leaves and branches. When combined with records from instrument towers, the data sets allowed the researchers to paint a richly detailed picture that shows spring starting earlier, and the growing season lasting longer than at any point in the past two decades.

Another important result, Richardson said, was the discovery of a significant source of error in existing computer models on how forest ecosystems work.

“This shows an opportunity to improve the models and how they simulate how forests will work under future climate scenarios forecast.” he said.

The real power of the findings, however, may be in helping to make the effects of climate change clearer to the public, the researchers said.