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

Between the years 535 and 536, a series of major global climatic events that took place that could easily be described as a global cataclysm with catastrophic consequences. The above abstract is from the sixth century historian and church leader, John of Ephesus, in his historical work, Church Histories (‘Historiae Ecclesiasticae’).

John of Ephesus is not the only one that mentions this event. Procopius lived between 500 and 565 AD and he was a late antiquities scholar and one of the main historians of the 6^th century. He also refers to the strange behaviour of the sun and believed that it was a bad sign and the beginning of other events.