Abstract
Reductions in Arctic sea ice may promote the negative phase of the North Atlantic Oscillation (NAO−). It has been argued that NAO-related variability can be used an as analogue to predict the effects of Arctic sea ice loss on mid-latitude weather. As NAO− events are associated with colder winters over Northern Europe, a negatively shifted NAO has been proposed as a dynamical pathway for Arctic sea ice loss to cause Northern European cooling. This study uses large-ensemble atmospheric simulations with prescribed ocean surface conditions to examine how seasonal-scale NAO− events are affected by Arctic sea ice loss. Despite an intensification of NAO− events, reflected by more prevalent easterly flow, sea ice loss does not lead to Northern European winter cooling and daily cold extremes actually decrease. The dynamical cooling from the changed NAO is ‘missing’, because it is offset (or exceeded) by a thermodynamical effect owing to advection of warmer air masses.
Highlights
Reductions in Arctic sea ice may promote the negative phase of the North Atlantic Oscillation (NAO À )
NAO À events are associated with raised heights over Greenland and depressed heights over the North Atlantic in low ice (LI) compared with high ice (HI)
Given the similarities between the mean atmospheric state during NAO À events and that often simulated in response to Arctic sea ice loss, the NAO has been suggested as a prototype to understand how mid-latitude weather might change with Arctic sea ice loss
Summary
Reductions in Arctic sea ice may promote the negative phase of the North Atlantic Oscillation (NAO À ). The response of the large-scale Northern Hemisphere atmospheric circulation to Arctic sea ice loss has proven hard to elucidate, owing to its inherent nonlinearity15–17—with respect to the magnitude and spatial pattern of sea ice loss[18,19,20,21] and to the background climatic state22,23—apparent model dependence[24], and often low detectability amidst the large chaotic variability of the system[25] Despite this large uncertainty, a common conclusion is that reductions in Arctic sea ice tend to favour a shift towards the negative phase of the NAO26, or its hemispheric equivalent, the Arctic Oscillation (AO). Extreme caution is required when extrapolating conclusions from one mid-latitude region to another
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