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 co ntrol experiments to investigate the role of the ocean-atmosphere coup ling and of diffusive heat uptake by the thermocline. The effect of va rying equilibrium climate sensitivity by varying the coupling of the a tmosphere and ocean is examined, high sensitivity being associated wit h weak coupling. A model representing a coupled land-ocean system, wit h a reasonably realistic representation of the large-scale physics is used. It is found that systems with large equilibrium sensitivities no t only respond somewhat more strongly to radiative perturbations but a lso return to equilibrium with much longer timescales. Based on this b ehavior pattern, we examine the model response to a series of volcanic eruptions following Krakatoa in 1883. Comparison between the model re sults 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 vol canic eruptions, the present study constitutes a possible test of diff erent assumptions about the sensitivity of the climate system.