There has yet to be a concrete physical explanation for the decadal variability observed in all analyses. Several modeling studies have been done to examine whether this variability is natural or anthropogenically forced [ammann et al., 2003; broccoli et al., 2003; church et al., 2005; delworth et al., 2005]. These studies showed that model OHCA are closest to observations when natural forcings, such as solar and volcanic, are applied. Delworth et al. [2005] and Church et al. [2005] cited several volcanic eruptions which caused oceanic cooling due to a negative impact on the net planetary radiative balance. Following the eruptions of Krakatau, Agung, Chichon and Mount Pinatubo, the surface temperature a few years after a volcanic event returned to the state before the eruption, but the subsurface cooled waters persisted on a decadal time scale, revealing one possible explanation for the observed variability in the first part of our study. More detection and attribution studies need to be done to further address this issue.