Very powerful volcanic eruptions send large amounts of ash high into the atmosphere, blocking sunlight and causing abnormally cold temperatures for a year or more after the eruption  In 44 B  C  there was a powerful eruption of Mount Etna in Sicily  In the following year, Chinese historians recorded summer frosts and dimmed sunlight in China, thousands of miles east of Sicily
If these phenomena were caused by volcanic ash in the atmosphere, then the ash sent into the atmosphere by Mount Etna' s eruption must have spread over great distances
the abnormal weather in China lasted for a full year or longer