Black swans are unforeseen, unusually large occurrences that have catastrophic results. For example, a huge volcanic eruption is a black swan event.
Almost every unusually cold summer over the past 2500 years was preceded by a volcanic eruption.
A really bad year for humanity and probably one of the worst years to be alive was 536 AD.
In early 536 a cataclysmic volcanic eruption in Iceland spewed ash that drifted across the Northern Hemisphere. Two other massive eruptions followed, in 540 and 547.
The resulting fog in 536 plunged Europe, the Middle East, and parts of Asia into darkness, day and night for 18 months. Temperatures in the summer of 536 fell 1.5°C to 2.5°C, initiating the coldest decade in the past 2300 years. Crops failed. People starved. Snow fell that summer in China.
Then, in 541, bubonic plague struck a Roman port in Egypt and spread rapidly, wiping out one-third to one-half of the population of the eastern Roman Empire.
Volcanic ash followed by plague, plunged Europe into economic stagnation that lasted until 640. Kinda puts things in perspective.