The volcanic cooling signals in ocean heat content can persist for much longer time (decadal or mutil-decadal time scale), far beyond the duration of volcanic forcing. Several studies have revealed that Krakatau's effect in the heat content can be as long as one-century. Relaxation time of the effects recent volcanoes is generally shorter than those before the 1950s. For example, the recovery time of ocean heat content of Pinatubo, which caused comparable radiative forcing to Krakatau, seems to be much shorter. The reason is that Pinatubo happened under a warm and non-stationary background with increasing greenhouse gas forcing. However, its signal still could penetrate down to ~1000 m deep.