“The Mysterious Deadly Frost of 1709 that Killed Thousands”, on the Grunge Channel (12 min, Aug 2021).
The worst year of the Little Ice Age, and it started with a cold snap on January 5, 1709 that didn’t let up until March.
Theories range from volcanic activity, to weak sunspot cycles (Maunder Minimum) to maybe some kind of disruption of the Gulf Stream, which is feared again.
Over 600,000 died and society became very unglued. The event may have made Russia stronger.
Wikipedia data charts, click for attribution on Maunder Minimum article