There were no supervolcanic eruptions that year, no evidence of meteor/comet impact. It’s theorized Iceland had an eruption that spread on the jet streams to affect the northern hemisphere, but the Smithsonian Global Volcanism Project has never reported a volcanic event higher than a VEI 6 (basically, amount of ejection and damage), and nothing higher than a 5 from the two most Speed Test active volcanoes of the period (Katla and Hekla).