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Scientists who study the world's climate have predicted that global warming could cause spring to start sooner. And that appears to be what's happening, at least in some places. Now, the signs vary, but as NPR's Christopher Joyce reports, you don't have to look around to see them - just follow your nose.

CHRISTOPHER JOYCE: If you're like me, spring arrives the day I wake up with a head like a balloon and a nose that's running faster than Usain Bolt. Spring means pollen and an early spring means...

DAVID SCHIMEL: Our noses start running earlier in the spring than they used to.

JOYCE: That's Dave Schimel, a scientist who runs the National Ecological Observatory Network, or NEON.

Now, noses aren't exactly scientific instruments. All sorts of things can make them run. So scientists look for other markers of spring. Schimel looks for them in the Rocky Mountains.

SCHIMEL: One of the most reliable ones is the timing of snowmelt. Looking back over those records retrospectively, one can see a very steady, progressive change towards earlier snowmelt and earlier runoff.

JOYCE: There are other signs too: lilacs or dogwoods are flowering earlier in many places, for example. Scientists who study how seasons affect plant and animal life cycles - it's called phenology - say on average, spring is coming several days earlier now than it did a few decades ago, something climate scientists say is a sign of a warming world.

And Schimel says early spring has consequences. For example, if snow melts earlier, the vegetation will suck up the water right away.

SCHIMEL: And the system dries out, which leaves a much longer dry spell for the rest of the summer and fairly dramatically increases the possibilities of wildfire.

JOYCE: The environmental group, Union of Concerned Scientists, is collecting data on early spring. Among those who are producing the data is Jake Weltzin, an ecologist at the U.S. Geological Survey. He points out that early spring may confuse plants and insects and make them shift their schedules - with unhappy results.

JAKE WELTZIN: So that a bee that's coming along and gathering pollen from plants might end up where there is no pollen available, because some of the plants have shifted earlier, and others haven't shifted at all.

JOYCE: To get a look at what early spring looks like on the ground, I visited Dennis Whigham, a botanist at the Smithsonian Environmental Research Center in Maryland. Whigham spends much of his time in the center's hardwood deciduous forest. He says many plants and trees - spring beauty, spicebush, oaks and maples - are emerging or flowering earlier than usual because of higher temperatures.

DENNIS WHIGHAM: If you look at one year compared to the next, you might not see that pattern, because some years are cooler in the spring than the previous year. But in general, it's clearly becoming warmer sooner.

JOYCE: Many plants remain dormant until soil and air temperatures get warm enough for a certain number of days; then they take off. Whigham finds one of spring's debutantes near a stream.

WHIGHAM: This is an understory herb - this particular one is called bloodroot. It's the first understory herb to appear in the spring, and so it has these lovely white flowers.

JOYCE: It's only a few inches tall with tiny white flowerlets. But this year it's behaved strangely. Normally, it flowers for two weeks, but like many plants this year in Whigham's forest, its life cycle has sped up.

WHIGHAM: And I noticed this year the flowers are - I was seeing them for only about a week, which again is this whole notion of everything being compressed because it was so warm.

JOYCE: Whigham says he doesn't know whether this hurried flowering is due to climate change or something else, but scientists say a warming climate may lead plants and animals to do some strange things.

And they may have to do some very strange things to survive where they are if springtimes continue to come earlier and temperatures keep rising. Either that, or hit the road and head north.

Christopher Joyce, NPR News.

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