Humidity is the great enemy of paper. High average humidity levels will rust staples and discolor paper over time. Warm, humid regions pose the greatest danger: Hawaii, Florida, the Gulf Coast. But even cool humid locations like Oregon or Maine are a threat.
Two Temple of Elemental Evil game books. Bottom book spent years in a storage locker, no climate control to lower humidity levels.
See Also: AD&D Module T1-4 “Temple of Elemental Evil” – 1ST PRINT IDENTIFICATION