Projected changes in regional weather patterns and associated temperature extremes arising from Arctic sea ice loss

Abstract:

The decline in Arctic sea ice cover has been widely documented and it is clear that this change is having profound impacts locally. An emerging and highly uncertain area of scientific research, however, is whether such Arctic change has a tangible effect on weather and climate at lower latitudes. Of particular societal relevance is the open question: will continued Arctic sea ice loss make mid-latitude weather more extreme? Here we analyse idealised atmospheric general circulation model simulations, using two independent models, both forced by projected Arctic sea ice loss in the late twenty-first century. The likelihood and duration of cold extremes are projected to decrease over high latitudes, and over central and eastern North America, but to increase over central Asia. Hot extremes are projected to increase in frequency and duration over high latitudes. We show that temperature extremes over central and eastern North America are more sensitive to Arctic sea ice loss than those over other mid-latitude regions. To better understand the drivers of these changes we utilise self-organising maps (SOMs) to identify the predominant regional weather patterns associated with surface temperature extremes. Then, the projected changes in temperature extremes are partitioned into dynamically and thermodynamically induced components. The former is estimated by examining the change in the frequency of occurrence of each pattern, whilst the latter is estimated from the change in the average number of temperature extremes associated with each pattern. We show that the contrasting responses over North America (fewer cold days) and central Asia (more cold days) can be largely explained by the differing relative importance of dynamics and thermodynamics in these two regions. Similar analyses for precipitation extremes will also be briefly discussed.