Global temperatures on the rise, and yet Toronto is in the midst of what may be one of the city's coldest winters on record.
How could this be?
Conor Anderson, an environmental science PhD student at the University of Toronto, has studied Toronto’s climate data – and has some theories.
In a Q&A blog post, Anderson said our current cold snap and the previous coldest winters of the past 30 years (1993-94, 2013-14, and 2014-15) all included the jet stream veering south, bringing cold, polar air for extended periods – sometimes for 25 days or more in a row.
What has climate change got to do with it?
Anderson's research suggests that the jet stream itself is weakening due to a warming climate, allowing arctic air to push southward. "This in turn," he said, "has led to colder recent winters in Toronto, which seems counter-intuitive."
Overall, Toronto winter temperatures have warmed considerably since winter 1840/41. But since winter 1985/86, there was a significant expansion of extremes partly due to anomalies in the position of the polar jet stream over Toronto.
It's entirely possible that these cold snaps are a complication of climate change. Anderson said, "More and more climate scientists are focusing on the impact of climate change on extremes rather than average conditions, and these extremes can be cold ones as well as warm ones."