A review of studies of effects of temperature, moisture, solar radiation, and other aggressive environmental factors on the properties of polymer composite materials are presented to substantiate the mechanism of their aging in extremely cold climates. It has been shown that composites develop internal stresses caused by unequal thermal expansion of reinforcing fibers and polymer matrices. These internal stresses cause the occurrence of microcracks, their coalescence, and formation of macro-damages in the bulk of the binder or at the interface with fibers. Fiberglass, carbon fiber, and other reinforced materials exposed to climatic conditions can accumulate water in pores and capillaries, which can turn into a solid phase at temperatures below 0 °C and increase internal stresses. Even in cold climates, the surface of materials undergoes destruction and microcracking under the impacts of UV components of solar radiation, thus increasing the number of sources of internal stresses. The mechanical properties of composite materials deteriorate under the effects of seasonal and daily thermal cycles.