Preprints
https://doi.org/10.5194/acp-2022-58
https://doi.org/10.5194/acp-2022-58
 
03 Feb 2022
03 Feb 2022
Status: a revised version of this preprint is currently under review for the journal ACP.

Volcanic stratospheric injections up to 160 Tg(S) yield a Eurasian winter warming indistinguishable from internal variability

Kevin DallaSanta1,2 and Lorenzo M. Polvani2,3,4 Kevin DallaSanta and Lorenzo M. Polvani
  • 1NASA Goddard Institute for Space Studies, New York, New York, USA
  • 2Department of Applied Physics and Applied Mathematics, Columbia University, New York, New York, USA
  • 3Department of Earth and Environmental Sciences, Columbia University, New York, New York, USA
  • 4Lamont-Doherty Earth Observatory, Columbia University, Palisades, New York, USA

Abstract. Early observational and modeling work suggested that low-latitude volcanic eruptions, comparable to the one of Pinatubo in 1991 or Krakatau in 1883, cause substantial surface warming over the northern continents at midlatitudes in wintertime. The proposed mechanism consists of the formation of an anomalously strong equator-to-pole temperature gradient in the stratosphere due to the presence of volcanic aerosols in the tropics, which is accompanied by an acceleration of the stratospheric polar vortex, which then shifts the Northern Annular Mode into a positive phase, resulting in warming surface temperatures over Eurasia.

However, a large body of research in the last decade has shown that, for eruptions such as Pinatubo or Krakatau, no such warming is seen in simulation with more recent climate models which, in general, have much finer vertical and horizontal resolution than the early ones, and which have separated the forced response from the internal variability by using large ensembles of integrations. Since the proposed mechanism is fundamentally sound, it is then possible that the 1991 Pinatubo eruption is simply not strong enough, but larger ones might indeed cause Eurasian surface warming in winter.

In this study, we explore this possibility using a state-of-the-art, stratosphere-resolving climate model, forced with prescribed volcanic aerosols from the Easy Volcanic Aerosol protocol. We consider eruptions with stratospheric sulfur injections of 5, 10, 20, 40, 80, and 160 Tg(S). With 20-member ensembles, we find that with injections of 20 Tg(S) or more – roughly twice the amplitude of Pinatubo and Krakatau eruptions – our model simulates a winter surface warming over Eurasia, which is statistically significant with a t-test given our 20-member ensembles. However, for all injection masses up to 160 Tg(S), the forced volcanic signal on Eurasian winter surface temperatures is so small as to be practically indistinguishable from internal variability.

Kevin DallaSanta and Lorenzo M. Polvani

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on acp-2022-58', Alan Robock, 19 Feb 2022
  • RC2: 'Comment on acp-2022-58', Anonymous Referee #2, 13 Mar 2022
  • AC1: 'Comment on acp-2022-58', Lorenzo Polvani, 09 May 2022

Kevin DallaSanta and Lorenzo M. Polvani

Kevin DallaSanta and Lorenzo M. Polvani

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Short summary
Volcanic eruptions cool the earth by reducing the amount of sunlight reaching the surface. Paradoxically, it has been suggested they may also warm the surface, but the evidence for this is scant. Here, we show that a small warming can be seen in a climate model for large enough eruptions. However, even for eruptions much larger than any of the ones that have occurred in the last two millennia, post-eruption warm winters are indistinguishable from those occurring without a prior eruption.
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