Why is the global climatic cataclysm of the sixth century virtually unheard of?

Why is the global climatic cataclysm of the sixth century virtually unheard of?
There was a sign from the sun, the like of which had never been seen and reported before. The sun became dark and its darkness lasted for 18 months. Each day, it shone for about four hours, and still this light was only a feeble shadow. Everyone declared that the sun would never recover its full light again. Historiae Ecclesiasticae