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The blizzard of 2016 was influenced by manmade global warming

The blizzard of 2016 was an exceptional storm that broke all-time snowfall records in multiple locations. Yet for many people it hit, this storm was not a complete shock; a string of severe winter storms have slammed the East Coast in recent years.

This could be random chance, since the atmosphere does tend to unleash more major winter storms during some decades compared to others. Or it could be due to another factor: Manmade global warming could be tilting the scale in favor of exceptional snowfall outcomes. Many scientists are beginning to suspect that this is the case.

In New York’s Central Park, for example, the 26.8 inches of snow was just one-tenth of an inch shy of tying the all-time record for the biggest snowstorm at that location, and greater than the city typically receives in an entire winter. But it was also the sixth top-10 snowstorm to hit the city since the year 2000. And the record of 26.9 inches was set recently — in 2006.

In Boston, which was spared the worst of this storm, five out of 10 of the biggest snowstorms have occurred since 2000 (or six, if one goes back a bit further to April 1997). Two of those five occurred last year alone.

In Washington, four of the city’s top-10 snowstorms have occurred since the year 2000.

In Philadelphia, enough snow fell during this one storm — 22.4 inches — as usually falls in an average winter season. The storm total was the fourth-largest on record in the city’s history, and the fourth storm since 2000 to rank in the top 10 list. (Weather records there date back to the 1870s.)

One of the main reasons for suspecting that climate change is playing a role, though perhaps not the dominant one, has to do with the milder-than-average sea surface temperatures off the East Coast.

This was an extraordinarily moisture-rich storm, with a direct connection to tropical air surging northward from the Bahamas, across the mild waters of the Gulf Stream, then westward over still more milder-than-average seas, before wringing the moisture out in the form of snow.

More than two inches of water equivalent, which is the amount of water contained in the snow if you melted all of it, fell in New York and Washington, with similar amounts in parts of New Jersey.

With 2015 being the warmest year on record, and another record or near-record anticipated next year, should East Coast residents batten down the hatches for more blizzards to come?

East Coast snowstorms are more common even as the world warms

Studies have shown that there’s a trend in the Northeast toward more frequent heavy snowstorms, even as average winter temperatures are increasing, in keeping with global warming.

There is also a national trend toward more frequent, heavy precipitation events. This shift toward heavier rain and snowstorms has been tied to global warming, which increases air and ocean temperatures and boosts the amount of moisture in the air.

Jay Lawrimore, a senior scientist at the National Centers for Environmental Information in Asheville, North Carolina, says that as the climate has warmed, years with “heavy seasonal snow and extreme snowstorms continue to occur with great frequency.”

He has published research showing that the frequency of extreme snowstorms has increased in the eastern two-thirds of the U.S. during the past 50 years. “Approximately twice as many extreme U.S. snowstorms occurred in the latter half of the 20th century than the first,” he wrote in an email to Mashable.

“Conditions that influence the severity of eastern U.S. snowstorms include warmer-than-average ocean surface temperatures in the Atlantic. These can lead to exceptionally high amounts of moisture flowing into a storm and contribute to greater intensification of the storm,” he wrote.

Unusually high ocean surface temperatures were present with this storm, with sea surface temperature anomalies of up to 6 degrees Fahrenheit off the Mid-Atlantic coast.

Sea surface temperature anomalies were also a factor that contributed to the Feb. 5-6, 2010 snowstorm that hit Washington with 17.8 inches of snow. That storm, dubbed “Snowmageddon,” was the city’s fourth-largest on record at the time.

A portion of the sea surface temperature anomalies can be traced back to global warming, while other factors also come into play.

“The ocean surface temperatures at any time are affected by natural variability, but as global surface temperatures increase, the temperature at any time is higher than what it would have been without climate change,” Lawrimore said.

Global ocean surface temperatures have increased at a rate of about 0.18 degrees Fahrenheit per decade since 1950, according to Lawrimore.

Judah Cohen, director of seasonal forecasting at the private weather company AER, toldMashable that he thinks the string of blockbuster East Coast snowstorms is connected to global warming, but that it’s not a clear-cut of a relationship.

“I truly believe that the streak of blockbuster snowstorms is not random or by chance but a symptom of a changing climate,”

“I truly believe that the streak of blockbuster snowstorms is not random or by chance but a symptom of a changing climate,” he said in an email.

“The warm sea surface temperature anomalies off the East Coast are impressive and certainly suggest more energy or fuel for these storms.”

However, he says it is too simplistic an argument to say that more moisture automatically equals bigger snowstorms, since other factors are also involved. These additional factors include atmospheric circulation patterns that may be more favorable for strong storms to develop and track along the East Coast.

Cohen noted that there is not a simple, direct connection between warmer seas and air temperatures and more extreme snowstorms in a particular location. Many more factors come into play, such as prevailing atmospheric circulation patterns including possible changes to the prevailing winter jet stream.

“I am still cautious to make the simple and admittedly intuitive argument a warmer atmosphere holds more moisture leading to greater snowfalls,” he said.

El Niño

In addition to global warming, there is the large role that El Niño plays in these storms, too.

Severe snowstorms are about twice as likely to occur in the Northeast and Southeast during El Niño winters

Severe snowstorms are about twice as likely to occur in the Northeast and Southeast during El Niño winters compared to years when there is no El Niño or La Niña present in the Pacific Ocean, Lawrimore said.

“It is to be determined the role that factors such as ocean surface temperatures, the influence of El Niño, conditions in the Arctic, and other factors have had on the severity of this week’s snowstorm,” he said.

Right now, a record-strong El Niño is in the process of peaking in the tropical Pacific, altering weather patterns worldwide.

This made the blizzard of 2016 more likely to occur, even if global warming influenced its severity.

Gulf Stream slowdown?

A more novel idea of what’s behind the increase in blockbuster East Coast snowstorms is the slowing down of the Gulf Stream current, which is formally known as the Atlantic Meridional Overturning Circulation (AMOC). Studies show that the Gulf Stream may be slowing down due in part to glacier melt runoff from Greenland.

This freshwater is less dense than the salty waters of the North Atlantic, and it tends to sit on the surface of the sea, rather than sinking to deeper depths as denser, saltier waters do in this area.

The AMOC involves the northward movement of warm, salty water in the upper layers of the Atlantic, as well as the southward return flow of cold, dense water in the deep Atlantic. It is sometimes known as the “Global Conveyor Belt.”

This conveyor belt can weaken if enough freshwater is added in just the right place, since it would reduce the return flow of dense water, like a person slowing down the turning of a hand crank.

According to Stefan Rahmstorf, scientist with Germany’s Potsdam Institute for Climate Impact Research who has studied the Gulf Stream slowdown, the weakening of this current has favored the development of unusually mild waters off the East Coast. Meanwhile, it has also created a cold pool of water south of Greenland. This cold pool sticks out on climate maps, since it’s the only area that was significantly cooler than average during the record warm year in 2015.

Writing for the climate science blog RealClimate, Rahmstorf said the slowdown of the Gulf Stream could set the East Coast up for more years with extreme winter storms, since it favors the continuation of warmer than average waters just off the coast.

“The warm sea surface temperatures are not just some short-term anomaly but are part of a long-term observed warming trend, in which ocean temperatures off the U.S. East Coast are warming faster than global average temperatures,” Rahmstorf wrote.

Rahmstorf is a co-author of a 2014 paper in the journal Nature Climate Change that found evidence of a significant slowdown in the Gulf Stream. A study published earlier this yearfound that high-resolution climate models project that — in large part because of the slowing Gulf Stream — the waters off the East Coast could warm nearly three times faster than the global average during the next several decades.

This slowdown and warming is, in turn, accentuating sea-level rise along the East Coast, leading to a regional sea-level rise hot spot that worsens coastal flooding in storms like the most recent blizzard. Cape May, New Jersey and Lewes, Delaware both set new all-time coastal flooding records during the blizzard.

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