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.

Earth System Model Response to Large Midlatitude and High‐latitude Volcanic Eruptions

“…This result confirms the finding of the climate response to volcanic eruptions mediated by ocean heat uptake in the previous climate model studies (e.g., Gregory et al, 2016;Gupta & Marshall, 2018;Merlis et al, 2014). Gupta and Marshall (2018) suggest that the ocean heat exchange parameter significantly exceeds the climate feedback parameter in the immediate aftermath of a volcanic eruption. In our model, the ocean heat exchange parameter is estimated at 8.4 W·m −2 ·°C −1 from the climate feedback parameter, 1.6 W·m −2 ·°C −1 (MRI Climate General Circulation Model, version 3 in Table 1 of Gregory et al, 2016), and the climate resistance (the sum of the two parameters, the inverse of the transient climate response parameter; Gregory et al, 2016), 10 W·m −2 ·°C −1 .…”

“…This value is about five times smaller than evaluated under atmospheric CO 2 concentration increasing at 1 % yr −1 for AOGCMs (Table 1 of Gregory et al, ). This result confirms the finding of the climate response to volcanic eruptions mediated by ocean heat uptake in the previous climate model studies (e.g., Gregory et al, ; Gupta & Marshall, ; Merlis et al, ). Gupta and Marshall () suggest that the ocean heat exchange parameter significantly exceeds the climate feedback parameter in the immediate aftermath of a volcanic eruption.…”

Comparing the spatial patterns of climate change in the 9th and 5th millennia B.P. from TRACE-21 model simulations

“…Further studies of the role of external forcing are needed to provide a better understanding of such mechanisms (cf. Ottera et al, 2010;Gupta and Marshall, 2018). Nevertheless, we conclude from the model simulations that the "4.2ka B.P.…”

Triggering Global Climate Transitions through Volcanic Eruptions

“…For step forcing experiments, the insolation is changed abruptly at t = 0 and subsequently held constant in time. For volcanic forcing experiments, we crudely emulate the effects of stratospheric aerosol injection by uniformly reducing the insolation for one year and subsequently turning the forcing off (as in Gupta and Marshall (2018)). We also conduct simulations comprising successive eruptions separated by a specified time interval.…”

“…This mechanism can shield the cold temperature anomaly away from atmospheric damping processes acting at the surface for decades to centuries (e.g. Stouffer (2004), Stenchikov et al (2009), Gupta and Marshall (2018)). The peak cooling in the abyss is set by enhanced deep convection around the poles, particularly at the sea ice margin in the SH (see Figure S2).…”