Abstract

AbstractThe effects of Arctic sea ice loss on cold air outbreaks (CAOs) in midlatitudes remain unclear. Previous studies have defined CAOs relative to the present‐day climate, but changes in CAOs, defined in such a way, may reflect changes in mean climate and not in weather variability, and society is more sensitive to the latter. Here we revisit this topic but applying changing temperature thresholds relating to climate conditions of the time. CAOs do not change in frequency or duration in response to projected sea ice loss. However, they become less severe, mainly due to advection of warmed polar air, since the dynamics associated with the occurrence of CAOs are largely not affected. CAOs weaken even in midlatitude regions where the winter mean temperature decreases in response to Arctic sea ice loss. These results are robustly simulated by two atmospheric models prescribed with differing future sea ice states and in transient runs where external forcings are included.

Highlights

  • Cold air outbreaks (CAOs) are persistent events of intrusions of cold air into warmer regions

  • The frequency and duration of cold air outbreaks (CAOs) do not show any robust change in the future, either in response to solely Arctic sea ice loss or in response to increasing greenhouse gas (GHG) concentrations, in either model, or in either the mid-21st century (M21) or late 21st century (L21) (Figure S2 in the supporting information)

  • In the rest of our analysis we focus on three midlatitude areas in different continents which warrant more detailed analysis due to their high population and noteworthy aspects of the simulated changes

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Summary

Introduction

Cold air outbreaks (CAOs) are persistent events of intrusions of cold air into warmer regions. In the Northern Hemisphere (NH), they are often linked to the occurrence of blocking highs (BHs) [e.g., Walsh et al, 2001] with frequently dramatic effects on society, agriculture, and economy of the affected areas. In spite of the global warming trend, a high number of CAOs have occurred in NH midlatitudes, and several studies have cited the rapid warming of the Arctic in recent decades as a potential cause [e.g., Petoukhov and Semenov, 2010; Francis and Vavrus, 2012]. Its effects are reinforced by other factors such as local radiative feedbacks owing to the stable Arctic lower atmosphere [Bintanja et al, 2011; Pithan and Mauritsen, 2014] and changes in water vapor content [Screen and Simmonds, 2010]

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