On the climatic implications of volcanic cooling

A simple energy balance model is used to investigate the response to a volcanic-type radiative forcing under different assumptions about the climatic sensitivity of the system. Volcanic eruptions are used as control experiments to investigate the role of the ocean-atmosphere coupling and of diffusive heat uptake by the thermocline. The effect of varying equilibrium climate sensitivity by varying the coupling of the atmosphere and ocean is examined, high sensitivity being associated with weak coupling. A model representing a coupled land-ocean system, with a reasonably realistic representation of the large-scale physics is used. It is found that systems with large equilibrium sensitivities not only respond somewhat more strongly to radiative perturbations but also return to equilibrium with much longer timescales. Based on this behavior pattern, we examine the model response to a series of volcanic eruptions following Krakatoa in 1883. Comparison between the model results and past temperature records seems to suggest that use of small sensitivity parameters is more appropriate. Despite the uncertainties associated with both the physics and the quantitative characteristics of the radiative forcing and the temperature anomalies produced by volcanic eruptions, the present study constitutes a possible test of different assumptions about the sensitivity of the climate system.