Just found this -- main factors towards paper 
decay is the environment. Paper decays faster in 
hot, humid, and polluted climates. High 
temperatures are very bad for paper. Even if 
exposed for a short period of time, most paper 
will become brittle at high temps. As a rule of 
thumb, for every increase of 6 C or 11 F, the 
life of paper is halved. The average wood pulp 
book will last 100 years if stored at 20C before 
becoming fatally brittle.  

If you need reassurance, I have a book that's 60 
years old, and even though the paper is yellowed 
at the edges, it's not the slightest bit brittle.