Climate: Whatever happened to 19 degrees?
"Whatever happened to 19 degrees?" my friend Tracy asked. It was January 2017. We wanted to go for a ski. The temperatures had been below zero, dampening our enthusiasm. Now, they were in the low 30s and a freezing drizzle was expected.
The same pattern has been occurring this winter. We experience extreme lows along with abnormal highs. What did happen to those perfect ski conditions, hovering around 19 degrees? And while we're asking, what's up with the highly unusual weather in other parts of the country, like the terrific storm that blew snow into Florida last week? Or the warmth in Alaska in December that wreaked havoc on the ice and snow?
A little research solves many mysteries at once. It all comes from understanding the polar jet stream — that current of air that runs around the Northern Hemisphere. In decades past, this "stream" ran fairly even — a straight river, with predictable undulations, flowing west to east.
Temperatures on the ground were fairly even and rose predictably with a drop in latitude. So if it was 20 degrees below zero in northern Minnesota, it would be 0 the Twin Cities, 20 in Des Moines and 30 in Kansas City — a regular low for all.
In recent years, the jet stream's waves have tended to "wind" like a curvy river, dipping deeply into the lower latitudes, or dipping high into the Arctic. So when we get very low temperatures, we are on the high side of the "dip," or curve, in the stream.
When this dip is deep or wide enough, the lows begin to look outlandish. So we see snow in Florida. When it "dips" up north, as it did in December, Alaska actually experiences weather from the southern "shore" of the stream. This stream isn't just undulating — it is rounding the bend.
The cause of this "wobbling" is a warming Arctic. The jet stream is created by the difference in temperatures between the cold Arctic air on one side of the stream and warmer temperatures on the other side. When open water replaces ice in the Arctic, warming occurs more quickly because heat is absorbed in the dark water.
With Arctic temperatures rising faster than temperate ones, the difference is less, and the stream weakens. When it weakens, it wobbles.
I am starting to sound like Dr. Seuss! I hope you have stuck with me. With no end in sight to the warming planet — the Arctic warming the fastest — this trend looks likely to continue.
But who am I to say? Anything that changes fast is less predictable. (Just live with a teenager for a few days and you will know what I mean.) Even scientists who know the most do not know what will happen next, though I've been impressed with their educated guesses thus far.
Common sense and our human aversion to risk tells me that we must all act as if we do not prefer unpredictability — even if it's pleasant to walk around outside this week.
Katya Gordon is a volunteer for the Citizens' Climate Lobby and a resident of Two Harbors.