Still, weather and climate specialists caution against using a litany of the period's frigid bluster or relative warmth to draw conclusions one way or the other about global warming.
Week in and week out, natural variations in weather "are far greater than any climate-change signal," says Michael Halpert, deputy director of the National Weather Service's Climate Prediction Center. Winter temperatures in North Dakota can range from 30 below zero F to 50 above. Against such strong seasonal temperature swings, "folks living in North Dakota aren't going to see that it's a degree warmer or a degree colder" based on long-term trends in global average temperatures, he adds.
Even when global warming becomes apparent – from decades to a century away – "winter will still happen, with cold spells and severe weather," says Gerald Meehl, a research scientist at the National Center for Atmospheric Research in Boulder, Colo. "But the trend will be toward fewer cold spells and fewer severe weather events."
From North America's standpoint, many forecasters point to La NiÃ±a, El NiÃ±o's climatological sister, as the key driver behind this past winter's offerings. Under La NiÃ±a conditions, warm water pools in the western tropical Pacific while waters in the eastern Pacific grow colder.