It's all in how long you want the books to last without degrading. If the answer is around a decade, you're fine, you'll do a little damage but not much. If the answer is 30-50 years or more and we assume the pages are white today (I'm sure many aren't), then the pages are highly likely to go offwhite or cream in this environment while in your possession.
The average collector barely cares about offwhite and cream pages with raw books in hand, so storage in highish temperatures is deceptively safe to people who largely ignore page color. Books can go from white to offwhite after 10-20 years in 80-90 degree temps, but to most people, that's no change at all, although obviously since CGC started noting page quality in addition to the numerical grade, this has gained a LOT more attention from the high-end collector.