Spring is coming. What does it mean in a warming world?

The vernal equinox is the day when the tilt of the planet’s axis is inclined neither toward nor away from the sun. (This also happens during the autumnal equinox at the beginning of fall, and of course the dates are reversed for the Southern Hemisphere.) Wherever you are in the world, the season officially begins at 12:57 p.m. ET on March 20.

The fall and spring equinoxes, for starters, are the only two times during the year when the sun rises due east and sets due west, according to Alan MacRobert, a senior editor with Sky & Telescope magazine.

The equinoxes are also the only days of the year when a person standing on the Equator can see the sun passing directly overhead.

On the Northern Hemisphere’s vernal equinox day, a person at the North Pole would see the sun skimming across the horizon, beginning six months of uninterrupted daylight.

A person at the South Pole would also see the sun skim the horizon, but it would signal the start of six months of darkness.

Though the equinox arrives consistently on March 20, climate change is helping alter the timing of spring in the U.S. Researchers looking at “first leaf” date for a number of plants as a proxy for spring saw that spring started 3 days earlier during the period of 1991-2010 compared to 1961-1980. Parts of the country including the Southwest, Mid-Atlantic and Northeast are seeing spring arrive up to a week sooner. That’s a comparatively small increase, but it could upset a balance that plants and animals have developed over hundreds, if not thousands, of years.

According to a long-term research project done in Colorado’s Rocky Mountains, for instance spring in that region now begins, on average, about three weeks earlier than it did in the 1970s.

New research shows that alpine snow in the Rockies now melts earlier in the year than it did when the project started 39 years ago, and begins to pile up later in the fall—allowing flowers to pop sooner, peak earlier, and last longer. A earlier blooming season can also place wildflowers in danger if they’re hit by a late frost.

Those things all add up and start cascading through the community and having bigger effects on the ecosystem.


Cover image from: Timandate.com

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