the weather changes
In her monologue, Titania describes all the changes that the world has been going through since she and Oberon started fighting. She begins her list of changes in weather by saying "Therefore the winds, piping to us in vain, As in revenge, have suck'd up from the sea Contagious fogs". This shows that the winds have shifted and the world has gone foggy--and that is just the first of all the terrible things she lists.
