Data on accelerated ageing and the effect of temperature and relative humidity (RH) are reviewed for paper, film and magnetic media studies. The activation energy for most paper and film studies falls in the range (80 to 120) kJmol^-1. For decay in magnetic media binder and yellowing of damar resin, the activation energies fall in a lower range, (60 to 80) kJ mol^-1. The average activation energy value of 100 kJmol^-1 implies a rule of thumb: double the lifetime for each 5 C drop, so 70 kJmol^-1 implies 7 C. A theoretical derivation from transition state theory suggests that these approximate rules are predictable and, hence, universal for materials in museums with chemical instability problems. The available data on relative humidity dependence suggests that half the relative humidity will more than double lifetimes for acid hydrolysis. Hence, the title of this article holds generally for museums. A graph of constant lifetimes on the psychrometric chart is presented. -- CCI=IC