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The winter season is half over, but snow began falling in New York City only last week. The snow that did fall seemed more like an afterthought, a half-hearted sprinkling that scarcely covered the ground.
Similar scenarios have repeated in other cities across the United States and in Europe, where unusually warm weather has made it appear at times as if Mother Nature is skipping winter and leaping directly into spring.
Walk the streets and you'll hear people say, either jokingly or with worried expressions, that global warming is to blame.
But is it really? Yes and no, scientists say. While global warming can't be linked to any one warm winter, it does make it more likely that a warm winter will occur [chart].
Global warming's effects will vary tremendously by location, however, fueling in some regions more rain or less, stronger or weaker winds and even possibly colder temperatures at the bottom of the planet.
Michael Mann, a meteorologist at Pennsylvania State University, compares it to fixing dice. Suppose you take a die, erase the three, and replace it with a six.
"If you roll that die, you're going to find that sixes come up twice as often as they should," Mann explained. But no particular six rolled can be attributed to the fixing because chance dictates it happen one-sixth of the time anyway. "That's sort of an analogy for what we see with climate change: As warm winters become more prevalent, we can't say that that particular one was due to climate change, but what we can see is that sixes are coming up more often than they should be."
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El Niño
Global warming isn't the only reason Central Park and other typically white locales lack their blanket of snow. Scientists think a cyclical warming of the Pacific Ocean, called El Niño, has also contributed to warmer winters. El Niño occurs every three to five years on average and leads to warmer winters in the upper half of the United States, but colder winters in the lower half. It works out to make the overall average temperature across the nation a little above normal.
"Global warming is like, year on year, giving a small push toward warmer winters," explained Gavin Schmidt, a climate scientist at NASA's Goddard Institute for Space Studies in New York. "El Niño, when it happens, gives a push towards warmer winters in this part of the world. Both are going on now."
Add to this mix the well-known, but oft-misunderstood phenomenon called "weather," which describes the daily or even hourly variations in temperature, rainfall and humidity that occur within a region.
"If we go back and look at those couple of 70-degree days in Boston a couple weeks back, or this record-breaking cold snap that's destroyed a large part of the citrus fruit crop in California, that's weather," Mann told LiveScience. "There's no way to attribute those individual episodes in any way to climate, let alone climate change."
Only by examining weather over seasons or years do scientists begin to enter the realm of climate, which is weather averaged over a long period of time.
"You can't take any one warm spell and say that was climate change," Mann said. "But the fact that they're occurring more often and more consistently, in part we may be seeing climate change loading the dice."
A record year
The current warm spell affecting the East Coast and much of the Midwest marks the second unusually balmy winter in a row for the United States. Together, the two consecutive spring-like winters, as well as last year's warmer than average summer, led the National Oceanic and Atmospheric Administration (NOAA) to recently declare that 2006 was the country's warmest year on record.
According to NOAA, the average temperature for the contiguous United States in 2006 was 55 degrees Fahrenheit, more than two degrees warmer than the average for the last century [chart].
But it is not one warm winter, or even one record-breaking warm year, that concerns scientists. They're fretting about the prospect of several warm winters, and several warm years, in the coming decades. And it is a prospect that seems more and more likely.
Next week, the Intergovernmental Panel on Climate Change (IPCC), the main international body tasked with studying climate change, is expected to release the first section of a four-part report that is expected to be the strongest statement yet by scientists that the burning of fossil fuels by humans over the past half century is warming the planet.
"If the models are correct, we've only seen the tip of the iceberg," Mann said. The 1-degree Fahrenheit warming that is occurring now could ultimately become 3 to 10 degrees.
Enormous impact
The impact of such a change on the planet, and on us, will be enormous, scientists say. Not all parts of the planet will be affected equally. While some regions will experience warmer winters, others might see more rain, or no rain, or less snow, or stronger hurricanes, or weaker winds.
Some places, like the interior of Antarctica, could actually experience colder winters if global warming continues. This, too, is predicted by the models.
"It has to do with the way that anthropogenic climate change influences the wind patterns in the Southern Hemisphere," Mann explained. "One of the consequences is that you get a tighter band of westerly winds in the southern latitudes that confines the cold air that's produced there, so you actually get a cooling."
There are a few upsides for life in a warmer world, such as less need for energy to warm homes during winter, but the benefits of global warming are expected to be overshadowed by its disadvantages the longer it continues.
"Economically, for one warm winter, there are winners and losers," Schmidt told LiveScience. "And all those plusses and minuses are extremely difficult to tally up. In not that many years, we'll be way out of the noise. It will be obvious to everybody that things have changed. Then you're not talking about plusses and minuses. It's going to be a net minus for everybody."
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