While many Cornellians are enjoying the recent spat of warm weather, the warmer-than-usual winter has been causing problems for the natural world throughout the U.S, according to recent Cornell research. The mild winter has caused animals to prematurely awaken from hibernation, plants to bud early and thrown the delicate dynamics of ecosystems off balance, a phenomenon dubbed “The Jumanji Effect.”
Wildlife specialist Prof. Paul Curtis, natural resources, has observed the effects of weird warmth on hibernating animals. He and other scientists have found that black bears, for example, are starting to awaken from their usual October to March slumber sometime in mid-February in areas across the U.S. At this time of the year, there is little food available for these animals and many of them resort to ravaging human resources for sustenance, Curtis said. In their search for food, prematurely awakened animals like black bears may dig through garbage cans, forage on farms or raid bird feeders—all acts that can damage local resident’s property and harm agricultural systems.
Day length is the primary factor for determining when animals become active after hibernation. Currently, the day length is too short for animals to rouse from hibernation, but because of the warm weather and lack of snow many animals take little effect to the day length and awaken early in the winter to look for food. Although it is possible for animals to resume hibernation, they only do so if the outside world is still in a “wintery” state, Curtis said. Even if the weather feels like spring and there is no food available for the animals, it is unlikely that they will resume hibernation even if it is still winter.
According to Curtis, warm winters such as this year’s can also cause population bursts in non-hibernating animal populations, because these animals experience less winter related fatalities in winters with warm weather. The growing deer population is an example of such a population boom. Population booms cause animals like deer to deplete their food supply earlier in the year than they normally would. This forces many of the animals to search for different food options, which has a ripple effect on the ecosystem.
Higher deer populations can cause an increase in tick populations and the incidence of lyme disease. Based on a survey conducted in 2002, Curtis said, deer populations cause 59 million dollars in agricultural losses in the state of New York. He also said that vehicle accidents involving deer are density dependent. When there is a large deer population, the number of car accidents increases substantially causing monetary losses and injuries to humans.
The warm weather is causing many plants to bud early, said Curtis. This has the potential to hurt both the ecosystem and human populations. Creating buds is fairly energy intensive for plants because they need to use energy stores that they received from photosynthesis. The buds cannot tolerate temperatures below freezing, and sometimes the cold winter weather persists after periods of warm weather. Plant populations can be negatively affected because if a bud dies, there will be no flower, and without a flower there will be no seeds.
“For many of our fruiting trees, such as apples that have fruiting blossoms, if the blossoms come out early and then suffer a hard freeze, those trees are done for the year. They aren’t going to produce any fruit in the fall, which is definitely a risk,” Curtis said.
According to Prof. Arthur Degaetano, earth and atmospheric sciences, this type of winter is caused not by climate change, but rather by a combination of La Niña conditions in the Pacific and strong pressure systems in the North Atlantic. When the North Atlantic Oscillation has stronger high and low pressure systems than usual, air is pulled across North America at a rate faster than usual. This creates a pressure barrier across the continent. The cold air that usually comes down through North America from the Arctic is then trapped above the eastward flow of air being pulled toward the Atlantic by the strong North Atlantic Oscillation. As a result places close to the Arctic Circle are experiencing freezing winters because the frigid air is trapped above North America.
The North Atlantic Oscillation is created by the low and high-pressure systems that result from air rising and descending in a pattern known as Hadley and Ferrel cells. Warm air at the equator rises and falls around 30˚ North and South, creating a high-pressure system. Ferrel cells, which circulate air from approximately 30˚ to approximately 60˚, cause a low-pressure system at 60˚ where air is rising back into the Ferrel cell or heading north into the Polar Cell.
The cold air coming down into the United States from the arctic is part of the Arctic Oscillation. When the cold air gets trapped above North America by eastward sweeping winds, the Arctic Oscillation is said to be positive. Although the winter temperatures are normal given the circumstances of a positive Arctic Oscillation paired with a La Niña year, there are problems associated with this type of weather.
Although it is not entirely clear what role La Niña plays in this scenario, the combination of a positive Arctic Oscillation and La Niña consistently results in this type of weather, according to Degatano.
Although climate change is not the main culprit for this winter’s warm temperatures, people should still be wary of its ranging effects, said Degaetano. Since the 1990’s there have been five of the ten warmest winters in the past 150 years, something that some see as indicative of a changing climate.
“The rate of change we’re seeing in warming right now over the past couple decades is higher than we’ve seen in any other time that people have been able to measure” Curtis said. Species that depend on a winter period, or that live at high elevations will be severely affected according to Curtis.