Winter's been so mild in much of the United States this year that you can slip out some sunny afternoons to the golf course or bike path. Many snow shovels have stayed in storage. Heating bills have fallen.
Meanwhile, Europe's suffering a brutal winter.
But in the USA, in the East, Midwest, Texas, the Plains and parts of the West, the average mean temperature was 5 degrees or more above normal over the past 30 days. Only Washington state and parts of Oregon showed cooler-than-average temperatures then.
It remains to be seen, however, whether U.S. winter records will be broken.
"We'll have to wait until February is over," said Kathryn Vreeland, a climatologist at the Northeast Regional Climate Center.
While Whatcom County has had a few days of sun and above-average high temperatures, nights have been frosty, and the typical rainy February weather is on the horizon for the next several days.
Mike Halpert, the deputy director of the government's Climate Prediction Center, said the U.S. had had a number of warm winters recently. But the last two were cold across much of the country, and that's fresh in everyone's mind, he said.
Part of the explanation for this year's mildness stems from the Arctic Oscillation — atmospheric pressure patterns in the Arctic and northern-middle latitudes.
The Arctic Oscillation has been in a warm or positive phase recently, meaning the polar jet stream is stronger than average and has shifted poleward, Halpert said. "Basically, that keeps cold air bottled up over the pole."
The last two winters were the opposite: A negative phase allowed cold air to drop down. That brought heavy snow to New York and New England last year, and the big snows in the mid-Atlantic in 2010.
Record keeping on the Arctic Oscillation began around 1950, Halpert said. In the 1950s, '60s and '70s, there often was a negative phase, bringing colder winters. In the 1980s, '90s and 2000s, many winters had a positive oscillation.
The Arctic Oscillation is part of the planet's natural cycle, Halpert said; it's too early to tell whether climate change is having an impact on it.
In the last couple of weeks, the Arctic Oscillation turned negative again, bringing severe cold to Europe and Asia, but not to the United States. That's partly due to another pattern of pressure, the North Atlantic Oscillation, Halpert said. That's remained positive.
It's also a La Nina winter, when cooler temperatures in the Pacific typically result in cooler temperatures in the Northwest. La Nina also directs storm tracks, shifting them away from the southeast toward the west and north, Halpert said.
While weather varies with each season and year, climate scientists worldwide have observed a longer-term global warming trend. They've reached a consensus that it can be explained only by the increase in greenhouse gases in the atmosphere, mainly as a result of burning fossil fuels.
Some climate research aims to see whether there are links between global warming and changes in the Arctic Oscillation.
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