Just a few degrees was the difference between bare ground and a winter wonderland in D.C.’s urban core last week. Would the storm, which was a disappointment to so many Washingtonian snow lovers, have played out differently had it occurred 100 years ago? Historical data say yes.
Since the late 1800s, the average temperature in Washington, D.C. during March has warmed at a rate of about 4.6 degrees (F) per century. Meanwhile, the average March snowfall has declined at a rate of 3.3 inches per century. Whereas the normal snowfall in Washington in March was 4 to 5 inches in the early 1900s, it’s now down to 1.3 inches.
During the Snowquester, Reagan National Airport’s temperature varied between 34 and 37 degrees during the first 12-14 hours of the storm, when snow or a mix of rain and snow fell. Had those temperatures been a few degrees cooler, no doubt snow would’ve lasted longer, not mixed with as much rain and more than 0.2 inches of snow would have accumulated. I’d speculate a few inches would have piled up, about the amount that fell at Dulles Airport.
(Let me clear that I’m not blaming our flawed forecast on global warming. If anything, we should’ve taken the evolved climate into account.)
Chip Knappenberger and Pat Michaels, climatologists affiliated with the libertarian Cato Institute and skeptical of dire climate change predictions, concede the “non-record-breaking non-extreme non-snowstorm” was “consistent with global warming.” But they conclude the involved interplay between global warming and complicated storm processes make it “virtually impossible to know” the overall effect.
I agree with Michaels and Knappenberger that global warming affects storms in ways we can’t quantify. But I don’t think we need to have that all figured out to accept a little nudge from climate warming can have big effects when it comes to rain versus snow.
As the climate has warmed in the U.S., observational evidence suggests the balance of snow versus rain in the U.S. has already shifted. Data featured in EPA’s 2012 climate change indicator report show many regions (see above) getting smaller portions of their overall precipitation as snow since around 1950 (although there does not appear to be a statistically significant trend around Washington, D.C.)
New projections from NOAA’s Geophysical Fluid Dynamics Laboratory show substantial reductions in future snowfall amounts (see above). About 40 to 60 percent less snow is expected in the Mid-Atlantic by the end of this century given a continued build-up in greenhouse gas concentrations.
To be sure, the increasing greenhouse gas concentrations are just part of the equation when it comes to rising temperatures and declining snowfall in D.C. Urbanization has also likely played a major role, with the heat dome built into the city’s core expanding and strengthening.
As the intensifying heat island and greenhouse effect continue to exert pressure on the climate in the coming decades, snow lovers may find themselves increasingly depressed in Washington, particularly when it’s just the matter of a few degrees. Forecasters should take note, too, and perhaps dampen their predictions under such circumstances.