Does it seem like snowfall is exhibiting manic behavior - lashing out with paralyzing blizzards one winter and retreating with piddling dustings the next? Is this the new normal for our winter climate in a globally-warmed world?
The Associated Press’ Seth Borenstein, in his piece “Climate contradiction: less snow, more blizzards” makes a fairly compelling case that yes, expect more winters with underwhelming snow amounts. But, when the big one comes, be prepared to get buried. Examining Washington, D.C.’s snowfall data, the idea appears to have merit - at least from our limited sample*.
Since the mid-1980s, Washington, D.C.’s winters have played out exactly as Borenstein describes, with feast or famine snow totals and, generally, declining amounts.
In the 30 winters since 1984 (including this year, assuming we don’t miraculously get 14 inches of snow in the coming weeks), only 5 winters have had above average snowfall in D.C. - compared to 25 winters with average to below average amounts (15.4 inches or less). In 4 of the 5 winters with above average snowfall, the total was 2 to more than 3 times normal - or 30.1 to 56.1 inches (in 1987, 1996, 2003, and 2010). Or, put another away, the 25 snow-deprived winters averaged 9 inches of snow, the 5 snowy winters averaged 40 inches.
Our average annual snowfall total has shrunk in this span, the 30-year average dropping from over 18 inches in 1984 to 14-15 inches as of this year.
We’ve also seen a tendency for fewer early season and late season snows in recent decades. All five of Washington, D.C. latest measurable snows on record (in April) occurred before 1960. And Washington, D.C. has not experienced accumulating snow in November in the last 16 years, the longest stretch on record.
Borenstein, who interviews a number of climate scientists to make his case, presents a fairly simple hypothesis. That is, as temperatures warm, the snow season shortens and locations on the margin of rain and snow, more frequently get rain. But, when big storms come along, they drop more snow (assuming it’s cold enough) since warmer air can hold more water.
“Shorter snow season, less snow overall, but the occasional knockout punch,” Princeton University climate scientist Michael Oppenheimer told Borenstein. “That’s the new world we live in.”
The shrinking snow trend may have just gotten started. Borenstein writes that a forthcoming study projects a 30 to 70 percent decrease in snow over the United States by the end of the century.
In short, for snow lovers, Washington, D.C.’s snow downfall may be exhilarating, but ultimately excruciating.
Some more technical notes
While Washington, D.C.’s recent snowfall history certainly fits into Borenstein’s narrative of less snow overall with the occasional biggie, I stop short of saying global warming causes big snowstorms.
It’s certainly reasonable to expect East Coast snowstorms affecting our region to be more juicy due to rising ocean temperatures (which can add moisture), but the configuration of natural weather patterns and the availability of cold air are much more important factors in the set up for historic snowstorms in our region.
I suspect the extreme nature of Washington’s recent feast or famine snowfall pattern, while enhanced and shaped by global warming, has been driven to a degree by randomness. Think of global warming playing more on the margins. It eats away at possible accumulation when temperatures barely support snow but perhaps adds a little extra in those rare cases when all the necessary ingredients for a whopper are in place. Because cold air is so often lacking in the D.C. area, this dynamic chips away at snow averages in the long run.
* D.C.’s recent snow history may or may not be representative of other cities in the region and across the U.S. Additional analysis would be required to determine whether the changes observed in D.C. are systemic or whether D.C. is on its own (for now) and perhaps just a harbinger of the future in some other cities**.
** In cities (farther north) where cold air is seldom in short supply for snow, global warming might serve to increase snow averages due to more available moisture even while shortening the snow season. (For the entire Northern Hemisphere, there is compelling data showing snow cover has rapidly declined in spring while holding more or less steady in winter.)