When I was a kid, I read a fiction novel about the Norse Gods, focusing a lot on the Fimbulwinter prior to Ragnorak. It was published prior to 1983. All I can recall about it was that the cover was white and light green. I know it's not much to go on, but if anyone has any information I'd be extremely grateful.
day of the giants lester del rey
or possibly the first of the incomplete enchanter stories The Roaring Trumpet by L. Sprague de Camp & Fletcher Pratt
