As the first signs of winter push into the Northeast, researchers have some good news for fair weather fans — spring is coming earlier than it used to. The lilacs say so.
In one of the most comprehensive studies that plants in the Northeast are responding to the global warming trend, Cornell scientists and their colleagues at the University of Wisconsin found lilacs are blooming about four days earlier than they did in 1965.
David Wolfe, a plant ecology professor at Cornell whose research will be published in a forthcoming issue of the International Journal of Biometeorology, said nature's calendar is changing due to an increase in greenhouse gases.
"It's not just the weather data telling us there is a warming trend going on. We are now seeing the living world responding to the climate change as well," Wolfe said Tuesday.
The Cornell study is consistent with other examinations involving the biological impact of rising temperatures, but those studies have been much more limited in geographic scope.
Earlier this year, Harvard University scientists also reported finding evidence of earlier flowering in specimens at the Arnold Arboretum in Boston, while botanists at the Smithsonian Institution in Washington, D.C. found the city's Japanese cherry trees are blooming about a week earlier than they were 30 years ago.
According to the Northeast Regional Climate Center at Cornell, the average annual temperature in the Northeast has increased by 1.8 degrees Fahrenheit since 1900, which is slightly higher than the global average of 1.1 degrees Fahrenheit.
The greatest rate of warming, though, has occurred during the winter months (December to February) with an average increase of almost 3 degrees Fahrenheit over the past 100 years — a rate that has accelerated over the past 30 years to 4.4 degrees Fahrenheit, Wolfe said.
Cornell researchers analyzed data from 72 locations throughout the Northeast where genetically identical lilacs were planted during the 1960s and 1970s as part of a joint U.S. Department of Agriculture-funded project involving Cornell and the University of Vermont.
The lilacs were planted to help farmers predict planting and harvest dates, but have now provided scientists with a historical record of bloom dates. The Cornell study also included apples and grapes at four sites in New York, which Wolfe said were blooming six to eight days earlier than in 1965.
While some may revel over an earlier-arriving spring, Wolfe cautioned that the warming trend has many implications — and not all good. It could, for example, favor some invasive species and alter important interactions between plants and pollinators, insect pests, diseases and weeds. "If the interdependence and synchrony between animals and plants are disrupted, the very survival of some species could be threatened," Wolfe said.
Climate change also could affect plant and bird migration patterns, animals' hibernation patterns, reproductive cycles, woodland composition, plant pathogens and the availability of plant food for insects and animals.
On the positive side, the warming trend is extending the growing season in the Northeast by several days — although hotter summers can negatively affect some crops, such as apples and grapes.
Most scientists anticipate the increase in greenhouse gases — and subsequently, the warming trend — will continue, so it's important researchers more broadly monitor the consequences for crops, animals and natural areas, Wolfe said.
Heat-trapping greenhouse gases such as carbon dioxide, nitrous oxide and methane are produced mainly by industry, automobiles and power plants. Climatologists say the gases absorb infrared radiation and trap heat in the atmosphere.