Insensitivity of global temperature response to the magnitude of volcanic eruptions

We investigate how the global mean temperature responds to single volcanic events of different magnitudes and to multiple events occurring close in time. We are using the Community Earth System Model version 2 (CESM2) to simulate the Earth system forced only with stratospheric aerosols from explosive volcanoes, with the rest of the climate system fixed at 1850 conditions. The model is run with a dynamical ocean component, and the Whole Atmosphere Community Climate Model version 6 (WACCM6) atmosphere component using middle atmosphere chemistry.

Previous efforts of estimating a response function assume a linear relationship between the forcing and the deterministic temperature response to the forcing [1], defined as T^det(t)=L[F(t)]. Studies also show that the forcing is similar across forcing agents [2] (although this is not a settled debate [3]), in which case volcanoes could provide a valuable means of estimating global temperature response to radiative forcing due to their short-lived and large temperature responses.

We present simulations of single volcano events with ejected sulphate aerosol loadings differing in orders of magnitude and simulations where two volcanic eruptions are close enough in time that the second eruption occurs as the temperature is still recovering from the first event.

We show that the functional form of the temperature response is similar for volcanic events of different magnitudes and that non-linearities are not important as a second eruption occurs when the temperature is well below equilibrium in a perturbed state. The results further suggest the global mean temperature time series may be reduced to a simple superposition of individual pulses, and thus that it may be described by a convolution between a linear response function and some forcing, analogous to the model used by [1].

[1] K. Rypdal and M. Rypdal, ‘Comment on “Scaling regimes and linear/nonlinear responses of last millennium climate to volcanic and solar forcing” by S. Lovejoy and C. Varotsos (2016)’, Earth System Dynamics, 2016, vol. 7, no. 3, pp. 597–609.
[2] T. B. Richardson et al., ‘Efficacy of Climate Forcings in PDRMIP Models’, Journal of Geophysical Research: Atmospheres, 2019, vol. 124, no. 23, pp. 12824–12844.
[3] P. Salvi, P. Ceppi, and J. M. Gregory, ‘Interpreting differences in radiative feedbacks from aerosols versus greenhouse gases’, Geophysical Research Letters, 2022, vol. 49, no. 8, p. e2022GL097766.