Another week, another nor'easter — the fourth powerful coastal storm of March 2018 put the big Northeast cities in its crosshairs. The region is notorious for vicious winter tempests, but four in one month seems a bit much, especially one on the first day of spring. March roared in like a lion. When's the lamb coming?
My New England neighborhood is usually peaceful at this time of year; the quiet interrupted only by honks of Canada geese, wind in the towering white pines; and the occasional hoot of a great horned owl. Not so much this winter. Rumbling generators, whining chain saws, and rattling snowplows lasted many days after each pasting by Mother Nature. We New Englanders love to talk about weather, and we revel in our toughness, but even that is different this year. After comparing stories of fallen trees and property damage, the conversation increasingly shifts to "Why?" Is there an explanation for this relentless, persistent parade of destructive cyclones, storms so strong that if you didn't check the calendar, you'd easily mistake them for hurricanes on the weather map? Perhaps.
Some climate change skeptics always use snowstorms to argue that the planet is not actually warming. President Trump, during a sharp December cold snap on the East Coast, suggested that "perhaps we could use a little bit of that good old global warming," which he has called a hoax in the past. Last April, conservative news outlets rejoiced when snow canceled a march in Colorado to protest Trump's climate policies. But rather than being evidence that climate change isn't happening, the extreme weather the United States has seen this month should be viewed as a sign that it is.
Although the atmosphere is a complex beast, researchers are fingerprinting a variety of ways that those increasing greenhouse gases are making winter storms more powerful and more likely. It's clear that this spate of nor'easters is being juiced by inordinately warm ocean temperatures along the East Coast, one of the key ingredients in the recipe for a bomb cyclone. Less intuitive, though, is the increasingly clear role being played by the rapidly warming and melting Arctic. A growing pile of studies suggests that heat waves in the far north are slowing the west winds of the jet stream, allowing the normally bottled-up frigid air to plunge southward in giant lobes.
For much of this winter, one of those cold lobes has been parked over the eastern United States — another key ingredient for coastal snowstorms. The bigger the lobe, the longer it tends to stick around, setting the stage for the parade of storms we've seen not only this month but during five of the last six winters as well. A study some colleagues and I published last week found that severe winters in the eastern United States were much more likely during Arctic heat waves — and this winter, the Arctic was particularly hot.
The western United States doesn't get off the hook, either. While the East shivers and shovels under the influence of the cold lobe, the West sits under a "ridge," a northward swing of the jet stream. Big ridges and deep lobes are two sides of a coin. The western ridge brought a record warm winter to Alaska and perpetuated California's drought, a pattern that only recently gave way to torrential rain. Research suggests that when we see low amounts of sea ice and warmth in the Bering Sea, as we have this winter, the northward loop strengthens along the West Coast. Strong ridges tend to hang around longer, earning this one the moniker "Ridiculously Resilient Ridge."
Not every winter will behave this way, though, as many factors influence the jet stream and our weather. While the globe warms overall — melting ice and snow at both poles — a few areas buck that trend with winter cooling. Eastern North America is one of those places. What does the future hold? Extreme weather of all sorts is a near certainty, except that fewer cold records will be broken. More "stuck" weather patterns are likely, punctuated with dramatic flips from one extreme to another. Remember the February heat wave when Bostonians flocked to the beaches? These "weather whiplash" events are also more likely.
Of course, nor'easters and western drought happened long before humans started messing with the planet, but it's becoming abundantly clear that the dice are now loaded for more extreme weather of all sorts. If we continue to burn fossil fuels, cut down forests, waste food and destroy natural systems, the problems facing our children will be even bigger than they already are. Stronger nor'easters, coastal flooding, more acidic oceans: These are symptoms of a disease that is still in our power to treat, but only if we administer strong medicine and soon.
Jennifer Francis is a research professor in the department of marine and coastal sciences at Rutgers University.