The Great Cataclysm had a severely detrimental effect on Earth's weather. One effect of this is the periodic occurence of Nega-Storms.
Nega-Storms have crimson colored acidic rain that is harmful but not deadly to humans. Their most dangerous aspect is the crimson Negative Lightning. People struck by it rarely survive. Thundarr managed to get struck by the Negative Lightning in Master of the Stolen Sunsword.