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Researchers Predict That Autumn Leaves Might Start Falling Earlier In The Future

ARI SHAPIRO, HOST:

Every year, summer turns to autumn, and leaves of gold and orange and red litter the ground. But why do leaves fall at all?

CONSTANTIN ZOHNER: They fall because it's getting cold, and they need to be protected against that.

SHAPIRO: Constantin Zohner is a climate change biologist at the Swiss Federal Institute of Technology. And he says the effects of global warming - hotter temperatures deeper into the year - led scientists to predict that trees would drop their leaves weeks later by the end of this century. Now his team says the opposite may be true. Writing in the journal Science, they say leaves may actually fall a few days earlier in the future. And the reason...

ZOHNER: The more productive plants are in the beginning of the season, in spring and summer, the earlier they stop being productive.

SHAPIRO: See, climate change also means an earlier spring. So trees are soaking up more sunshine and carbon dioxide earlier in the year. And when they are full, they drop their leaves. Christy Rollinson of The Morton Arboretum in Illinois compared it to Thanksgiving dinner.

CHRISTY ROLLINSON: If the tree is eating everything right away, like I want to do at grandma's table, it's going to fill up sooner. And so there's kind of these balancing mechanisms that happen within a tree that mean a tree can only eat so much carbon.

SHAPIRO: And that could have global implications for the uptake of carbon dioxide.

ROLLINSON: The timing of this leaf drop does indicate when trees kind of stop taking up carbon. And so there are also all of these global impacts for how much carbon a tree is able to take out of the air and what that means for future climate change and what we can expect and what we cannot expect.

SHAPIRO: And if nothing else, the findings mean leaf peepers can expect a slightly earlier flush of fall foliage in the years to come.

(SOUNDBITE OF MUSIC) Transcript provided by NPR, Copyright NPR.