The last three summers were the three hottest on record in Washington, D.C.. Meanwhile, since the mid-1990s, snowfall has been extaordinarily variable in our nation’s capital. Blockbuster snows crippled the city in 1996, 2003, and 2010, but in the intervening years, snow was hard to come by.
A new NOAA-led study “The recent shift in early summer Arctic atmospheric circulation” suggests declining Arctic sea ice may be playing a role in these kinds of extreme, fluctuating weather patterns, which may assert themselves even more in the coming decades.
Published today, the study provides evidence that high altitude winds that separate cold air from warm air - have become more wavy and meandering in recent years. Instead of moving right along from west to east, they have tended to plunge south and surge north.
This change, the authors suggest, may be playing a role in atypically warm and cold weather extending unusually far north and south at different times, and then staying put.
The study team analyzed sub-Arctic winds at an altitude of about 10,000 feet in the early summer from 2007-2012 and compared them to the average from 1981-2010. NOAA describes the shift in the winds the authors uncovered:
Before 2007, typical summer winds at the Arctic surface were more variable but tended to flow from the west. Since then, the summer winds were found to blow more consistently from the south, through the Bering Strait, across the North Pole, and out toward the Atlantic Ocean relative to the mean pattern in previous decades.
The shift coincided with the rapid decline of Arctic sea ice.
“This shift demonstrates a physical connection between reduced Arctic sea ice in the summer, loss of Greenland ice, and potentially, weather in North American and Europe,” said James Overland, of NOAA’s Pacific Marine Environmental Laboratory and study lead author.
The resulting meandering flow regime has often favored atmospheric blocking, where weather systems lock in place and get stuck. This means if it’s cold, warm or stormy, such conditions are likely to persist under these circumstances.
“Recent increases in the initiation, persistence, and severity of weather extremes around the hemisphere may be due, at least in part, to the high-latitude forcing of enhanced blocking, particularly over North America and the North Atlantic sectors of the Arctic,” the study says.
The study is careful to caution “spatial and intra- and interannual variability is to be expected” - meaning the pattern might lead to unusually warm conditions in one region and unusually cold conditions in another, and that conditions may fluctuate over time. For example, recall unusually cold conditions in parts of Europe last winter even while much of the U.S. experienced near record-warmth.
But some researchers have found the hypothesis that declining Arctic sea ice is leading to this more extreme flow pattern overly simplistic.
Climate Central’s Andrew Freedman, in article published in September, interviewed researchers who expressed some reservations about the hypothesis. Take for example, Randall Dole, deputy director for research at NOAA’s Earth System Research Laboratory, who said, “it cannot be assumed that the changes will necessarily make weather worse, at least by some metrics.”
Judah Cohen, a climate forecaster at Atmospheric and Environmental Research in Massachusetts added: “It is not simple to explain how sea ice loss that peaks in August and September impacts the circulation at mid-latitudes [during] December through March.”
Assuming these the atmosphere is transitioning towards a more wavy, wandering state due to the decline in Arctic sea ice, it doesn’t make predicting the future any easier NOAA says.
“Predicting those meanders and where the weather associated with them will be located in any given year, however, remains a challenge,” it writes.
Or as study co-author Jennifer Frances of Rutgers University wrote on this blog last month: “[A]t this point, I can only say that I think it’s going to be a very interesting winter.”