AMATEUR NATURALIST

Why is it so cold in winter?

Image courtesy of NASA/Goddard Space Flight Center Scientific Visualization Studio
Posted April 10, 2011, at 9:24 p.m.
Last modified April 12, 2011, at 7:24 a.m.

As usual, our notoriously harsh Northeast winter is still, in April, beating up on us. (In case you forgot, there was a blizzard on April 1. I measured an even 16 inches of snow on my deck that Saturday morning.) Why is it so cold in winter here?

Well first of all, the seasons come and go because Earth is tilted in relation to the sun. As we circle around every 365 or so days, the tilt alternately takes the Northern Hemisphere into and out of the sun’s directmost rays. In other words, during summer the sun’s rays strike us more or less directly; but in winter they’re at an angle, and for fewer hours, heating us up less. The farther north you go, the less direct sun you get and, in general, the colder it is. In the summer, we tilt more toward the sun, catch more direct rays for longer each day, and are warmer.

That accounts for summer and winter, but it doesn’t account for some perplexing variations in temperatures across the Northern Hemisphere. When I visited Iceland in a fit of youthful insanity a few decades ago, I was shocked to learn that the average wintertime temperature in Reykjavik is higher than New York City’s, even though Reykjavik is just above latitude 64 (the Arctic Circle itself is just a hop, skip and jump away at latitude 66 degrees, 33 minutes), while New York is just above latitude 40. And yet, the average low temperature in January for Reykjavik is 27, while in New York it’s 26. In Bangor, which is at latitude 44 degrees, 48 minutes, the average low January temperature is 8, according to weather.com.

How could Reykjavik be almost 20 degrees warmer on January nights than Bangor, which is way farther south?

Well, that’s not all. Most of Europe is farther north than us, and warmer. At almost exactly the same latitude as Bangor is Bordeaux, in southern France, where the average January low temperature is 36 and the average high 49. Bangor’s average January high is 26. London, England, which is just above 51 degrees north, has an average January high of 46 and low of 36, while Labrador City, Labrador — which must be one of the world capitals of cold if you ask me — at latitude 52 degrees, 56 minutes has an average January high of 2 and low of minus 18. Hexham, near the ancient Roman wall in northern England where I’ve spent some time, is farther north than Labrador at latitude 54, but its average January high temperature is 38. That’s plus 38. Labrador is plus 2.  

What is going on here? The Gulf Stream carries warm waters from the balmy Gulf of Mexico up past Newfoundland and washes around Iceland, Britain and the shores of France and Portugal, moderating air temperatures there year round. But that turns out to be a relatively minor factor. Some California Institute of Technology researchers recently reported that a greater impact is sort of the inverse.

The warmer water flowing along the East Coast toward Europe doesn’t heat Britain, France and Iceland as much as it freezes us. It warms the air above it and sets up atmospheric waves that actually suck cold air down from Arctic Canada to descend on the Northeast, encoldening us beyond our neighbors to the east. Interestingly, the same process works in the western Pacific, accounting for the similarly harsh winters experienced in China’s northeast.

So that goes a long way toward explaining it, but as usual the explanation doesn’t ease the beating. I’ve been in London during February and seen daffodils cheerfully abloom, to no one’s surprise there. Yet here it is April and 7 degrees of latitude farther south in Troy, and my old Mercedes is still completely buried in snow. The average high temperature for Bangor in April is supposedly 53, and the low 33. In the several Aprils I’ve spent in London, I remember no snow. Here, though, you’ve got to keep your defenses ready. We are not out of winter yet.

naturalist@dwildepress.net

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