A woman walks in blowing snow in downtown Boston, Thursday, Jan. 4, 2018. A massive winter storm swept from the Carolinas to Maine on Thursday, dumping snow along the coast and bringing strong winds that will usher in possible record-breaking cold. (AP Photo/Michael Dwyer)
The Associated Press

The recent brutal American cold snap was a freak of nature, scientists say, who added that such extreme cold is far less likely to occur than it used to.  

Specifically, the frigid, record-breaking two-week cold spell that began in late December is now 15 times rarer than it was a century ago, according to a team of international scientists who study if extreme weather events are natural or more likely to happen because of climate change.

"Cold waves like this occurred more frequently in the climate of a century ago and the temperature of two-week cold waves has increased throughout North America, which is consistent in a climate of global warming," said Geert Jan van Oldenborgh, a senior researcher at the Royal Netherlands Meteorological Institute.

The study by the World Weather Attribution group analyzed weather records dating back to 1880 and found the cold weather that hit a swath of the U.S. from Maine to Minnesota tends to happen once every 250 years. In the early 1900s, it happened about once every 17 years.

Climate change has made such cold spells less common and less intense, the group said. The scientists say cold waves are now, on average, approximately 4 degrees warmer than they used to be.

World Weather Attribution is an international effort to analyze the possible influence of climate change on extreme weather events, such as storms, extreme rainfall, heat waves, cold spells and droughts. It's a partnership of Climate Central and several universities.

Regarding a possible climate change link through the effects of lower sea ice extent in the Arctic, the research team said the climate pattern that led to this two-week cold period did not occur more frequently in recent years.

“We do not find any evidence of intensification of this type of cold wave due to climate change; in fact, the Arctic air moving south is now warmer, which accounts for the trend of warmer cold waves,” said Claudia Tebaldi, a science fellow at Climate Central.

They found that although this type of extreme cold event has decreased in both intensity and frequency over the last century, it will continue to occur.

“This cold wave was exceptional,” said Gabe Vecchi, a geoscientist at Princeton University, “for being 7°F to 11°F colder than the coldest two weeks in recent decades and for occurring so early in the season, especially in light of the decrease in intensity and frequency of cold waves over the past century.”

Meteorologist Ryan Maue of weather.us, who was not part of the World Weather Attribution team of researchers, said "this attribution study is a straightforward yet concise analysis of the recent record cold in the context of our historical records. From the recent National Academy 'attribution science' review, we have 'high certainty' and 'high confidence' in attributing the reduction in extreme cold events to human caused climate change." 

"The Climate Central led study conclusions fit exactly with that consensus opinion: less frequent and severe cold is a consequence of global warming."

However, Maue does not agree that global warming due to lack of Arctic ice can be directly linked in any way to these sort of cold waves, as some scientists have claimed: "Instead of baffling the public with emerging theories or counter-intuitive explanations, scientists should simply explain what we confidently know:  winters will still exhibit extreme cold for decades to come but the historical trend is toward less frequent and extreme cold due to global warming."

Contributing: The Associated Press