Oh yeah, Red Mountain's eruption during the First Era did cause climate change that affected plants as recorded by the http://www.imperial-library.info/obbooks/nirnroot_missive.shtml.
Sun's Death occurred near the end of Resdayn at 1E 668. http://www.imperial-library.info/pge3/other_lands.shtml, 6 centuries before.
Therefore, you have evidence that a Red Mountain eruption occurred at a time that caused frost fall in Atmora during the Merethic?