The analysis relies on a special “spring index,” which defines the start of spring as the point when temperatures allow for certain early-season events in plants, such as the emergence of leaves and blooms. The index was created using data that has been collected for a citizen science project over the past few decades, according to Jake Weltzin, executive director of the USA-National Phenology Network and an ecologist with the U.S. Geological Survey, which helped fund the project.

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Since the 1950s, volunteers have been collecting information about the leafing and blooming of certain plants, such as lilacs and honeysuckle, Weltzin said. More recently, climatologist Mark Schwartz of the University of Wisconsin at Milwaukee used this information to develop an algorithm that can be used with national temperature data to determine where and when “spring” has arrived across the country.

By comparing this year’s temperatures with data from previous years, the scientists are able to determine which locations are seeing an unusually early spring, compared with the average. Washington D.C., for instance, saw its spring arrive a whopping 22 days early, according to the analysis.

In general, the new season has already made its appearance throughout most of the Southeast and as far north as southern Illinois and Indiana. It’s now starting to show up scattered locations across the Western states, including in parts of Colorado, New Mexico and Arizona, and has begun to creep into California.

The same index was also used in a recent study that demonstrated that spring is arriving earlier and earlier in many national parks throughout the United States. Looking at data spanning the past 112 years, the study found that spring has been advancing in 76 percent of the nation’s national parks. And more than half of all parks are experiencing extreme early springs, compared with 95 percent of the historical record.

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These findings, along with the newly released maps of this year’s springs, are just another way of pointing to the progression of climate change, Weltzin noted. He also noted that, although the balmy conditions this February may seem nice on the surface, an early spring can come with all kinds of downsides. For one thing, the onset of warm weather is also associated with the reemergence of disease-carrying parasites and insects, such as ticks and mosquitoes.

It can also carry serious agricultural risks. Early springs are sometimes followed by sudden frosts or droughts later in the summer, which can be devastating for crops that have already begun to grow. It has happened several times in the recent past, Weltzin pointed out — in 2012, the grape harvest in Southwestern Michigan was ravaged by a sudden cold snap following an early spring, and a similar incident hammered the tree nut harvest in the Southeast in 2007, he said.



As far as the latest climate news goes, there are other indicators of the long-term climatic changes that are happening in the United States, Weltzin noted. But the onset of spring remains one of the more dramatic red flags.

“There’s actually some evidence that suggests that the timing of fall is changing, as well,” he said. “That’s a more complicated season, we don’t have as much data, but we are seeing some changes, and we are trying to better understand and describe what those are.”