Cold waves in North America are no longer as cold as a century ago

Zach MacGregor, of Framingham, Mass., clears snow from a sidewalk as a snowstorm begins, Thursday, Feb. 9, 2017, in downtown Wellesley, Mass. (AP Photo/Steven Senne)

Cold waves, like the recent one in the United States, are found to be 15x rarer in today’s climate than that of a century ago.

Says who? Read more about who the World Weather Attribution team is.

Read the full report below:

World Weather Attribution scientists have analyzed the 2017-2018 North American cold wave and have concluded that this type of event is approximately 15 times rarer in the current climate, as cold waves are now, on average, approximately 4°F (2°C) warmer than they used to be. This type of extreme cold event has decreased in both intensity and frequency over the last century, but continues to occur.

The 2017-2018 North American cold wave persisted from the last week of December 2017 through the first week of January 2018. During that time, many cities in the United States and Canada saw numerous record low daily maximum and minimum temperatures, record low wind chill temperatures, and record persistent cold conditions. According to the National Weather Service, Buffalo, New York had the coldest last seven days of the year since record keeping started in 1871. New York City’s temperature remained at or below 32°F for two weeks, which ranks among the top five records for the most consecutive number of days at or below freezing. Boston tied for consecutive days of temperatures at or below 20°F with a previous cold spell in 1917. Chicago’s 12 consecutive days below 20° tied a record seen only twice before in 1895 and 1936. The impacts of the cold have been far ranging. 22 deaths in the U.S. and two in Canada have been attributed to the cold wave. Wildlife has been affected by the extreme cold, as well: iguanas have been falling from trees in Florida, sea turtles have washed up on shores in Florida, and frozen sharks have been found on the shores of Cape Cod.

The WWA analysis looks at the coldest two week daily mean averaged temperatures between December 26, 2017 and January 8, 2018 in the northeastern U.S. and southeastern Canada. While the cold wave coincided with Winter Storm Grayson, the blizzard also known as a “bomb cyclone” that brought snow as far south as Florida and as far north as Maine, WWA researchers did not specifically address the blizzard in this analysis.

“This cold wave was exceptional,” said Gabe Vecchi, Professor of Geosciences and the Princeton Environmental Institute at Princeton University, “for being 7°F to 11°F (4°C to 6°C) 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.” As Geert Jan van Oldenborgh, senior researcher at the Royal Netherlands Meteorological Institute (KNMI), noted, “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.”

The scientists concurred that cold spells will continue to occur in the current climate and this cold wave exemplifies this understanding. As to whether climate change played a role in the cold wave, Claudia Tebaldi, a science fellow at Climate Central, explained, “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.” Regarding a possible climate change link through the effects of lower sea ice extent in the Arctic, the team showed that the circulation pattern that led to this two-week cold period did not occur more frequently in recent years.

The full paper can be found on the WWA website.

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