Like most everyone else, Texas state climatologist John Nielsen-Gammon has been feeling the chill lately. He's even taken to wearing a coat in his office at Texas A&M.
“My office has been in the 50s the past couple days,” he said Thursday.
Despite that inconvenience, he doesn’t see this winter as out of the ordinary when it comes to average temperatures.
Austin, for example, is running only about 1 degree Fahrenheit below its historic average temperature since the start of December, Nielsen-Gammon says, “which is not very far at all, given the normal variability of winter weather."
What sticks out isn’t the average temperature, but the extreme cold spells. We’ve had three cold fronts push in so far this year, something he calls “unusual, but it's still not exceptional.”
Why so many cold fronts? Basically, you can thank the jet stream. It’s a current of air that divides the cooler north from the warmer south.
Rich Segal, a meteorologist with Spectrum News, says the jet stream dipped farther south than usual three times this winter.
On Monday, "a big piece of that arctic air just started to move rather quickly through Canada [and] entered the United States," he says, "and that’s what gave us that the temperature drop.”
Often when that happens, you hear people say this: “Well, if the Earth is really warming, why is it so cold?” President Trump even tweeted something like that just a few weeks ago.
In the East, it could be the COLDEST New Year’s Eve on record. Perhaps we could use a little bit of that good old Global Warming that our Country, but not other countries, was going to pay TRILLIONS OF DOLLARS to protect against. Bundle up!
— Donald J. Trump (@realDonaldTrump) December 29, 2017
But Kerry Cook, a professor at UT Austin’s Jackson School of Geoscience, says that demonstrates a big misunderstanding of climate.
“It’s a local thing we have going on,” she says. “It’s not a global cooling.”
In fact, she says, the cool air may be getting farther south precisely because of warming in the north.
“When we have melting ice in the Arctic it actually warms the Arctic quite a bit and can modify the position of the jet stream,” says Cook, “so if the jet stream is coming down and dipping down over the eastern U.S. it’s going to bring very cold weather with it.”
She says the bottom line is, it’s temporary. The long-term and global trend is toward warming.
“We get record cold nowadays only about a fifth as frequently as we experience record warm temperatures," he says. "So, the number of record cold days has gone way down.”