When I first started digging into climate impacts, I used to think that the northeastern U.S., where I live, was a pretty good place to have landed. I still think so. It’s unlikely we’ll see historic mega-droughts, like those forecast by some for the U.S. Southwest. We’ll see heat that we’re far from prepared for, but it’ll be hotter still in the South. Our forests are expected to change, but they’re not under pressure like those in the Mountain West, nor are they currently experiencing rising risks of wildfire. We have our own problems, to be sure, like coastal vulnerability and trends in extreme precipitation.
But this week in the news there are two new studies that reminded me to expect the unexpected. While we understand the general pathway of change, the shorter-term directions the climate can take along the way can take us by surprise.
Exhibit A: Our winter
As of this writing, 101 inches or about 8 feet of snow has fallen in Boston over a two-month period. As the Washington Post recently summarized: “Boston is on pace for near-record snowfall for Anchorage, and has already eclipsed the 30-day snowfall record for Buffalo — a city known for its intense lake-effect fueled snowstorms.”
Are you one of the poor souls experiencing this winter in the greater Boston area? If so, you’ve done at least two of these three things: (1) stopped thinking about going anywhere, because really, how? (2) taken up wide-eyed head shaking when it comes to the weather, because really, what’s there to say? And (3) lost track of the weeks altogether, because how can spring be coming if it’s always 10 degrees?
Plus this year the groundhog bit a guy. If you’re not one of us, trust us: winter’s been a beast.
But at least it’s a rare event — I’ll probably never see this kind of thing again in my lifetime. Right? Sorry, my weary friends, but not necessarily.
New research tries to make sense of events like the Northeast’s frigid, snowy winter. While we know that not all cold spells are caused by the now nefarious “polar vortex,” this new work suggests that warming temperatures in the Arctic are weakening the boundary between the Arctic north and the warmer mid-latitudes. That weakening, in turn, appears to be slowing the jetstream’s normally speedy west-to-east course, sending it instead on meandering northern and southern waves.
Deep southerly dips of the jet stream allow icy Arctic air to extend southward. And in some instances, these loopy wave patterns hold in place for a week at a time. Or forever; it feels like forever at the moment. We saw this last year across the Midwest and Northeast, minus all the snow. (This year’s snowstorms and record accumulation appears to be attributable to record warm North Atlantic waters meeting our meandering jet stream along the New England coast.) There are plenty of other ideas in the mix, too.
(It’s worth pulling my head out of the Northeast long enough to acknowledge the astounding contrast between our winter and what’s happening on the West Coast and in Alaska, with record high temperatures and record low snowfall. As my colleague, Robert Mera, puts it we have two influential climate patterns at play here, in addition to the Arctic: the Pacific North American Pattern and the North Atlantic Oscillation, both natural patterns, but both in a positive phase, strongly influenced by record warm ocean temperatures, and “acting like bullies” as they escort the Arctic air southward.)
With the Arctic only getting warmer is there reason to think we won’t see this kind of cold and snow again? Hope springs eternal. In Ode to the West Wind, Shelley wrote “O Wind, If Winter comes, can Spring be far behind?” But weaken that wind and warm our oceans, and yes, spring can feel very far behind.
Exhibit B: Local sea levels
And then there are our seas. If you live in low-lying parts of the Northeast U.S., you know that coastal floods are happening more often during high tides. We released a report about this last fall. But amidst the data we used is an interesting phenomenon, recently explored in a new study.
About 6 years ago, the Northeast U.S. and parts of Canada saw a rapid, dramatic spike in sea levels – roughly 4 inches, and 5 outside of NYC. The cause? The new thinking is that the Gulf Stream, the ocean current which normally moves along the coast of North America, transporting warm tropical waters northeast, hit a bottleneck of sorts and that the water essentially piled up. But how?
Normally, when the Gulf Stream travels north, it meets with cold Arctic waters, cools, sinks and moves back toward the tropics, in a process widely thought of as the ocean “conveyor belt” (see figure). But in 2009, parts of the North Atlantic were unusually warm, so the current failed to cool, sink, and move along as usual, slowing by some 30 percent. Persistent winds served to drive this “extra” water ashore. Researchers believe that the warmer Arctic contributed to this spike in sea level.
The spike dropped after a roughly two-year period, but water levels have not returned to what they were previously. Such a spike is considered very unusual. But with sea level rising at an accelerating rate and the Arctic continuing to warm, they could become a feature of our coastal future.
Didn’t see THAT coming
What these two emerging pictures mean to me is that the storyline of climate change in the Northeast that I’ve had in mind probably has many more plot twists than I’d imagined. This is probably true in lots of places.
Yes, some underlying trends are quite clear: global average temperature is rising; if we remain on our current emissions pathway, we can expect staggering increases later this century; globally, sea level is rising at an accelerating rate and can’t simply be shut off. But whatever emissions pathway we end up taking, we will see continued changes in our climate, and some of them may take us by surprise because our climate is dynamic and complex.
Also dynamic and complex: us. 2015 can be – needs to be – a big year for climate action. I’m hoping it’s the chapter where we surprise ourselves, start bending the emissions curve in a serious way, and pre-empt those big, dangerous climate plot twists.
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