Global Warming Is Bringing Spring Earlier To The U.S.

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Yet another addition to the ever-expanding list of things that climate change is messing up: spring. According to new research, due to rising temperatures this season will be brought forward by three weeks in the U.S. over the century.

A shorter winter? Where do I sign up! Not so fast. This isn’t a cause for celebration or justification for a coal-burning party. Such a shift has implications for the growing season of plants and could create a mismatch between the availability of vegetation and the animals that depend on it, which is not good news. In addition, it could heighten the risk of so-called “false springs” whereby milder temperatures deceive vegetation into coming out of dormancy prematurely.

This isn’t actually the first study to describe a change in the timing of spring, or more specifically the onset of spring plant growth. This is generally assessed by looking at two easily measurable events: leaf emergence and flower emergence, or first bloom. Both temperature and day length, or photoperiod, play a big part in triggering these events, and while many studies have suggested a trend towards earlier onset amid increasing temperatures, others have observed the opposite, with such mixed results highlighting the difficulties of generating estimates of something so complex in nature.

Now armed with more data and better climate predictions, scientists from the University of Wisconsin-Madison took this opportunity to generate better models in order to create more reliable predictions of spring onset over the rest of the century.

For the study, published in Environmental Research Letters, the team used statistical models called the Extended Spring Indices (SI-x), which are based on leaf emergence and first bloom of three defined plant species, to project both spring onset and false springs across the U.S. up until 2100.

When considering the study region as a whole, they predict that spring onset will shift by a median of 23 days over the century, with the western U.S. and the Great Plains experiencing the biggest changes. Southern areas were found to be affected the least, although these regions already experience early springs.

“Our projections show that winter will be shorter – which sounds great for those of us in Wisconsin,” study coauthor Andrew Allstadt said in a statement. “But long distance migratory birds, for example, time their migration based on day length in their winter range. They may arrive in their breeding ground to find that the plant resources they require are already gone.”

Additionally, while false springs were projected to show an overall decrease, some areas, including parts of the Midwest are predicted to experience an increased risk, with freezing temperatures returning after plants have begun to wake up from dormancy. This is bad news for those regions, explains Allstadt, as these events can interfere with plant production systems, leading to significant crop losses if agricultural species are affected.

To paint a more comprehensive picture, the team is now extending the work to encompass extreme weather events such as droughts. Although things may sound a bit doom and gloom, it’s difficult at this time to predict how species will cope with such rapid changes. Birds are known to be able to adjust migration patterns, although some that have failed to do so in the past have shown population declines due to mismatches with their plant resources.

More work needs to be done, but to facilitate this the team has made available all of its data. 

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