This winter and last winter have been exceptionally, unseasonably warm. While there is still several months left of winter 2012-2013, winter of 2011-2012 was the fifth warmest winter on record in the Northeast. In Minneapolis, temperatures didn’t drop below zero until the 19th of January, which is a tie for the latest date for the temperature drop since record-keeping began in 1871.
For me, the warm weather and lack of any significant snowfall was a blessing because it meant dozens of hours saved that I otherwise would have been shoveling. If you live in a part of the country where winter temperatures a below freezing for weeks on end, these 45 degree days can seem very pleasant. But what are the effects of a warm winter on wildlife? How does it effect the Michigan ecosystem?
There are many downsides to having an overly mild winter. For one thing, the winter deep freeze usually kills off a large amount of insects that would otherwise breed and come out in force in the spring (although for insects that have a freeze-tolerance mechanism, a cold winter is irrelevant). Mosquitoes, ticks and fleas all are typically killed off in the winter – a milder winter means these creatures will be breeding earlier and we will consequently be dealing with potentially larger mosquito, tick and flea populations in the coming summer. Besides being irritating, pests coming out earlier might take a toll on fledgling plants coming up in the spring, especially wheat, which is already in the ground in the winter and could be a target of insects coming out earlier than usual.
Furthermore, when the temperature is warm, it sends a signal to plants that it is time to begin growing. Basically, warm temperatures in January can “fool” plants into thinking its April. Plants may begin to grow, bud, and cast off their winterized protections early. This is not a problem if the temperatures hold, but if it suddenly does become cold in, say February or early March, the sudden freeze can be deadly. This happened to Michigan’s apple crop last winter – warm temperatures caused apple trees to blossom prematurely, and then a sudden freeze in April killed off the majority of the young apples.
The same effect could occur with amphibians like frogs, who come out and breed when it gets warm. A warm winter coupled with a sudden freeze could decimate the frog population.
On the other hand, animals that do not hibernate, such a deer, may enjoy a population explosion. Without the scarcity that harsh winter conditions bring about, the deer population can increase dramatically, which of course could have reprecussions for the amount of deer collisions. This year, a mild winter followed by summer drought conditions brought about the spread of the disease EHD that killed off a great many deer, so the population increase was partially mitigated by the EHD die off. If summer of 2013 is not also a drought year, we will probably see the increase in deer population reflected in greater numbers of deer-related accidents. Higher deer populations can cause an increase in tick populations and the incidence of lyme disease.
This bizarre type of winter is not caused by climate change, as some have inferred, 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. Hopefully, this should be the last year of this cycle.