Proper compact disc storage, DVD, or Blu-ray storage conditions are required in order for these types of optical media to last many years. When discussing storage conditions we are usually talking about temperature and relative humidity levels.
Like most other storage media, cool temperature and lower relative humidity extend the lifetimes of information carriers and warmer temperature and high relative humidity conditions decrease lifetimes significantly. If you are storing very stable media such as the gold CD-R, then temperature and relative humidity storage conditions are less critical. However, for less stable media, controlling these two factors can make a large difference in lifetime and prevent the very early failure of these discs and loss of your digital information.
The acceptable temperature and relative humidity compact disc storage conditions, which are also valid for DVD storage and storage of most other optical discs as well, are given in the ISO standard (ISO 18925:2013 - Imaging materials - Optical disc media - Storage practices) for the storage of optical discs. This standard states that temperatures must be kept lower than 23 degrees Celsius. It is best not to exceed 25 degrees Celsius for extended periods of time and temperatures should NEVER exceed 32 degrees Celsius for any amount of time.
Monitoring of temperature and relative humidity can be performed with a device as shown below. There are many different types of these monitoring devices in various price ranges.
The average air conditioned home can maintain these minimum requirements on hot summer days. Without air conditioning, it is likely that on hot summer days the upper limit of 32 degrees Celsius will be exceeded and discs will have shorter lifetimes if kept under these conditions. However, lower temperatures will result in longer lifetimes. The standard for optical disc storage gives a lower limit of -10 degrees Celsius. It is generally not required to store CDs, DVDs, and Blu-ray discs at such low temperatures to get reasonable longevity (unless you are using very cheap and unstable disc media) and storage below about 12 degrees Celsius usually requires special packaging to prevent condensation on the discs. Removing discs from cold storage also requires slow warming to prevent possible delamination of disc layers.
The acceptable relative humidity range for compact disc storage or DVD storage is between 20 and 50%. Once again the drier the better for longevity but relative humidity for CD storage and other discs should be kept above 10%. Conditions that are too dry can lead to the delamination of disc layers.
Fluctuations in temperature and relative humidity should be minimized as much as possible, but generally the concern for CDs, DVDs, and other optical disc media is when rapid and large changes occur. As long as discs are not exposed to very large and rapid temperature and relative humidity changes, they should be fine.
Note that when Blu-ray, DVD, and CD storage of discs have been in conditions quite a bit different that the use environment, it is best to let the discs acclimatize to the use environment for one or two days prior to playing or reading them to ensure they play properly. Although the media is relatively waterproof, it can still absorb small amounts of moisture under certain conditions. This moisture can lead to slight changes in the dimensions of the optical disc and these small changes may be enough to affect the performance of the disc.