Robust winter warming over Eurasia under stratospheric sulfate geoengineering – the role of stratospheric dynamics

Antara Banerjee,Isla R Simpson,Amy H Butler,Lantao Sun,Lorenzo M Polvani,Alan Robock

doi:10.5194/acp-21-6985-2021

Abstract

Abstract. It has been suggested that increased stratospheric sulfate aerosol loadings following large, low latitude volcanic eruptions can lead to wintertime warming over Eurasia through dynamical stratosphere–troposphere coupling. We here investigate the proposed connection in the context of hypothetical future stratospheric sulfate geoengineering in the Geoengineering Large Ensemble simulations. In those geoengineering simulations, we find that stratospheric circulation anomalies that resemble the positive phase of the Northern Annular Mode in winter are a distinguishing climate response which is absent when increasing greenhouse gases alone are prescribed. This stratospheric dynamical response projects onto the positive phase of the North Atlantic Oscillation, leading to associated side effects of this climate intervention strategy, such as continental Eurasian warming and precipitation changes. Seasonality is a key signature of the dynamically driven surface response. We find an opposite response of the North Atlantic Oscillation in summer, when no dynamical role of the stratosphere is expected. The robustness of the wintertime forced response stands in contrast to previously proposed volcanic responses.

Highlights

Mitigation of greenhouse gas emissions remains of utmost importance in counteracting anthropogenic climate change
Precipitation trends in summer are reversed over Eurasia relative to winter (Fig. 1e), which is again suggestive of a stratospheric dynamical influence in winter
We have investigated the role of stratospheric dynamics for Northern Hemisphere regional climate changes under continuous and steadily increasing stratospheric sulfate injections to meet multiple annual mean surface temperature targets under the RCP8.5 scenario in the Geoengineering Large Ensemble (GLENS) simulations

Summary

Introduction

Mitigation of greenhouse gas emissions remains of utmost importance in counteracting anthropogenic climate change. Known as solar radiation management, describes one set of approaches which proposes to cool the planet by reflecting sunlight to space. Among these approaches, confidence is highest in stratospheric sulfate injections resulting in a net negative radiative forcing and, a cooling of the planet (Crutzen, 2006; MacMartin et al, 2018) through the scattering effect of sulfate aerosols. Compelling observational evidence for the global cooling effects of stratospheric sulfate aerosol is offered by large, low latitude volcanic eruptions which, to some extent, provide a natural analog for sulfate geoengineering.

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