The first day of spring isn’t what it used to be. In fact, over the past several decades spring weather has been arriving earlier in most parts of the United States. This shift affects all aspects of life — from when flowers bloom to when animals migrate and have babies — the very things that make spring magical.
The climatologist Mark D. Schwartz at the University of Wisconsin-Milwaukee and colleagues at the USA National Phenology Network have developed an index that can be used to estimate the date of the onset of the spring growing season (as opposed to the date in March when daylight and darkness are of equal length, the technical definition of the first day of spring, which falls on Tuesday). This “first leaf” index estimates the first day that leaves appear on plants. Here in the lower 48, spring now arrives approximately three days earlier. “First leaf” has gone from March 20 (1951-1980 average) to March 17 (1981-2010 average). This forward creep is consistent with the effects of an overall warming climate, roughly 1.4 degrees over the past century, what we refer to as global warming.
Winter 2012 will go down as the fourth warmest on record for the contiguous United States, according to the National Climatic Center. And so far, March will be remembered for the more than 2,200 warm temperature records that were set around the nation. The warm weather, with daytime high temperatures close to 40 degrees above average in some places (high temperature records are outpacing cold records by a ratio of about 19-to-1 so far this March), set the stage for severe thunderstorms that spawned rare, damaging tornadoes near Detroit. It used to be that a warm day in March felt like a gift, but now it feels as if we’re paying for it.
The real trouble lies in the fact that these changes create mismatches in how species interact. For example, the Stanford biologist Carol Boggs tells the story of the wildflower and the butterfly. Dr. Boggs has been tracking wildflowers and their pollinators for 40 years in the Colorado Rockies. The Mormon Fritillary butterfly (Speyeria mormonia) is a montane species that depends on the nectar of the Aspen Fleabane (Erigeron speciosus) — an alpine wildflower. Warmer springs mean that the flower buds of the Aspen Fleabane are emerging earlier, when frost is still a high risk. That risk translates into an increased incidence of frost damage, fewer wildflowers and fewer butterflies.
Examples like this highlight the fact that wildlife species will need help from us to rescue them from climate change. And we will need to accept that human activities like burning fossil fuels disrupt the well-tuned clockwork of nature. As a result, we need to be willing to both increase our overall energy efficiency and switch to renewable energy sources. At this point, nobody knows how well ecosystems will manage to overcome these timing glitches, but scientists do know that there will be big disruptions.
By Heidi Cullen, a scientist at Climate Central, a journalism and research organization and the author of The Weather of the Future: Heat Waves, Extreme Storms, and Other Scenes from a Climate-Changed Planet.