The recent deep freeze that shattered low-temperature records in Michigan and elsewhere across the U.S. was a freak of nature in terms of weather events, according to an international group of scientists who study climate.

The type of Arctic blast that hit Michigan on Christmas Day - and hung on for two weeks - is actually 15 times rarer than it was a century ago, according to World Weather Attribution.

The private organization analyzes current weather data to determine if extreme events are natural or due to climate change, the Associated Press said.

"It was very definitely strange, especially now," said study co-author Gabriel Vecchi of Princeton University. A century ago "it wouldn't have been that strange. Things like this are becoming stranger."

Among the group's findings:

Scientists found no evidence that this cold wave was made more intense by rapid Arctic warming.

This winter's coldest 2-week stretch so far has ranked as the sixth-coldest on record.

The last recent winter with a colder 2-week span? 1981/82.

The other four stretches of colder weather occurred before the 1920s.

By analyzing historical weather records, the team found that the spate of bitterly cold weather that gripped states from Maine west to Minnesota tends to happen about once every 250 years, the AP said.

Climate change has made these cold snaps less frequent, and less intense.

Last year, this same team of scientists determined many of the headline-making weather events - from Hurricane Harvey to heavy flooding in France - could be connected to man-made global warming.