The Climate Response to Multiple Volcanic Eruptions Mediated by Ocean Heat Uptake: Damping Processes and Accumulation Potential

Abstract

A hierarchy of models is used to explore the role of the ocean in mediating the response of the climate to a single volcanic eruption and to a series of eruptions by drawing cold temperature anomalies into its interior, as measured by the ocean heat exchange parameter q (W m-2 K-1). The response to a single (Pinatubo-like) eruption comprises two primary time scales: one fast (year) and one slow (decadal). Over the fast time scale, the ocean sequesters cooling anomalies induced by the eruption into its depth, enhancing the damping rate of sea surface temperature (SST) relative to that which would be expected if the atmosphere acted alone. This compromises the ability to constrain atmospheric feedback rates measured by λ (~1 W m-2 K-1) from study of the relaxation of SST back toward equilibrium, but yields information about the transient climate sensitivity proportional to λ + q. Our study suggests that q can significantly exceed λ in the immediate aftermath of an eruption. Shielded from damping to the atmosphere, the effect of the volcanic eruption persists on longer decadal time scales. We contrast the response to an "impulse" from that of a "step" in which the forcing is kept constant in time. Finally, we assess the "accumulation potential" of a succession of volcanic eruptions over time, a process that may in part explain the prolongation of cold surface temperatures experienced during, for example, the Little Ice Age.