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Modern scientists trying to understand climate change are engaged in an unlikely collaboration with two beloved but long-dead nature writers, Henry David Thoreau and Aldo Leopold. NPR's Elizabeth Shogren reports that the authors of "Walden" and "A Sandy County Almanac" are helping today's scientists predict how global warming will affect spring.

ELIZABETH SHOGREN, BYLINE: Boston University biology professor Richard Primack has been taking a cue from Henry David Thoreau.

RICHARD PRIMACK: So what Thoreau would do is he would go out for walks almost every day for about four hours and he would record in the spring when he saw the first open flower of particular species.

SHOGREN: Hundreds of different flowers around Walden Pond and elsewhere in Concord, Massachusetts, 160 years ago. Primack quotes Thoreau.

PRIMACK: "I often visited a particular plant four or five miles distant half a dozen times within a fortnight that I might know exactly when it opens."

And we do the same thing today.

SHOGREN: Over the past several years, Primack's team has recorded when these same flowers bloom. They learned that, on an average year, flowers will bloom about 11 days earlier than in Thoreau's time. Then something happened last year that made them ask a bigger question. Harvard biology professor Charles Davis is part of the team.

CHARLES DAVIS: In late December 2011 and January 2012, I started seeing irises blooming in the Boston area. And, you know, this is the dead of winter, and you can imagine it sort of rocked my world.

SHOGREN: This bizarre spring made them wonder. Is it possible to use historical records to predict when flowers will bloom during, especially, hot years? It turns out in Wisconsin, biologist Stanley Temple was working on a similar analysis using Aldo Leopold's journal entries, like this one.

DR. STANLEY TEMPLE: (Reading) Pasque flowers are blooming. Lilac leaves...

SHOGREN: Temple reads from the first week of May in 1940.

TEMPLE: (Reading) Service berry, choke berry are breaking buds. Pussy willows...

SHOGREN: Temple gathered lots of data over recent decades to compare with Leopold's. When last spring's temperatures in Wisconsin hit new highs, he was ready.

TEMPLE: It was when we realized, wow, 2012 is going to be a record setter, we decided to ask the question: Could we have predicted the flowering date given what was known about temperature? And indeed, we could have.

SHOGREN: The scientists in Massachusetts and Wisconsin combined their information and jointly published these findings this week in the journal PLOS ONE. They also showed that record temperatures last spring resulted in the earliest known flowering times for dozens of plants. Richard Primack says Thoreau would be amazed. Thoreau's records showed the first highbush blueberries always flowered in mid-May. But last year...

PRIMACK: It was actually flowering during the first week of April. So this was a plant species which has shifted its flowering time by five or six weeks from the time of Thoreau. So this is really quite unbelievable.

SHOGREN: Stanford biology professor Terry Root wasn't part of the study. She says before this study, scientists didn't know that plants would be able to keep blooming earlier and earlier as the globe warms. Now they do.

DR. TERRY ROOT: Is that good news or bad news? The answer to that is yes.

SHOGREN: Plants might benefit from longer growing seasons. But they could suffer if the insects that pollinate them don't adjust at the same rate. Root says since the unusually high temperatures last spring could be normal in a few decades...

ROOT: This is kind of a peek into the future.

SHOGREN: The scientists say they don't know yet whether spring flowers will be able to keep matching the pace if the planet gets even hotter. Elizabeth Shogren, NPR News.

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