The recent anniversary of the wreck of the Great Lakes ore ship Edmund Fitzgerald, memorialized by Canadian folk singer Gordon Lightfoot, recalled 29 sailors lost in an epic storm on Nov. 10, 1975, on Lake Gitche-Gumee.

Lightfoot invoked the Ojibwa legend of the “Witch of November,” said to blow at hurricane strength down the length of Lake Superior in autumn. Massive storms in 1913, 1940, and 1975 each bore witness to this legend.

This year she again unleashed a frightful blast, setting new temperature and snowfall records — even before November's arrival. Appropriately beginning on Halloween, heavy snow fell and temperatures plunged, disrupting lives across the Midwest and into the South.

How did this happen?

In 1988, James Hansen of NASA’s Goddard Institute for Space Studies, warned of imminent global warming triggered by carbon dioxide released from fossil fuels. A rising global average temperature in the 1980s and 1990s seemed to authenticate his warnings and to presage the coming of shorter, warmer winters.

Yet there has been little rise in global temperature, as measured in the atmosphere by two independent satellite systems. Surface measurements are also showing somewhat diminished warming since about 1997-’98.

Recent winters in the Midwest have featured the arrival of pre-chilled air from far-off Siberia, bringing bitter cold, unaccustomed across southern Canada and into the United States since the late 1970s. Climate scientists blamed it on an aberrant polar vortex.

The phenomenon is better explained as the result of the extraordinary buildup of cold-air masses over Siberia in October, held in place by stalled weather systems before releasing into North America.

In the Northern Hemisphere, the coldest temperatures originate in northeastern Asia, not over the Arctic Ocean (exclusive of Greenland). The record for low temperature at any permanent settlement north of the equator is owned by Oymyakon, Siberia at ˗96.2° F.

This year’s early arrival of winter, some six weeks premature, cannot be dismissed as “global cooling,” either. As someone once reflected, “One swallow does not a summer make.” Neither does one blizzard make a winter.

But the popular idea that steady carbon-dioxide increases would eventually render winters obsolete makes the recent untimely outbreaks of severe cold all the more perplexing.

Another 10 years may provide climate scientists with enough additional data to determine if carbon dioxide is actually the thermostat that controls global temperature. My own sense, for what it’s worth, is that carbon dioxide is not the exclusive thermostat but only one of a number of factors contributing to constantly changing climates.

The positioning of the great land masses on our planet has come about by slow continental drift. It currently favors the accumulation and preservation of snow and ice at high latitudes conducive to glacier formation. Likely it will remain so for many more million years.

During earlier geologic times, when the continents were differently situated, ocean currents flowed freely from the equator to the polar regions, distributing warmth that allowed vegetation and wildlife, now common only to temperate and tropical zones, to thrive near the poles. Modern North America and Eurasia lie in such a position to block the free flow of tropical currents into the Arctic Ocean.

It can be reasoned that a continuation of alternating warming and cooling, recurrent during the previous 10,000 years known as the Holocene Period, will persist into the near future.

The “Witch” waits for the return of another period of continental-scale glaciation that would plunge portions of the northern and southern hemispheres back into another 100,000-year deep freeze. She could then blow to her heart’s content.

William D. Balgord has a Ph.D. in geochemistry and is head of Environmental and Resources Technology in Middleton, Wis.