In this talk I will present my groups' recent thoughts and findings on links between the Arctic Amplification of climate change – enhanced warming of the Arctic relative to the global mean – over the last 2–3 decades and Northern Hemisphere (NH) midlatitude extreme weather. Improving our understanding of Arctic/midlatitude weather-climate linkages has the potential to enhance both subseasonal-to-seasonal weather prediction and long-term climate projections, as well as improve our understanding of societal and economic impacts: particularly on sectors like energy, water, agriculture, ecology, transport and tourism. Although global warming will increasingly make midlatitude cold-air outbreaks (CAOs) less severe, some recent studies argue that AA has contributed to more frequent severe weather in NH midlatitudes, including disruptive CAOs. In a warming climate CAOs could become more disruptive in many regions of North America and Eurasia even if their severity declines, especially if they do become more frequent, due to reduced preparedness and the potential for CAOs to still give widespread snow and frost. This raises a critical question: are trends in AA and CAOs coincidental, or is there a physical link between AA and extreme winter weather?

Severe winter weather events in the northern continents are often linked to the stratospheric polar vortex (SPV) and atmospheric blocking, but despite their importance these mechanisms are not well understood. Here I review recent research advances and paradigms including: (1) a nonlinear theory of atmospheric blocking that helps to explain the location, timing and duration of AA/midlatitude weather connections; and (2) studies of the SPV’s zonal asymmetric and intra-seasonal variations, its southward migration over continents, and its surface impacts. A full understanding of SPV variability may have been hampered by the predominant research focus on sudden stratospheric warmings. I make recommendations for future work that can leverage recent theoretical and empirical insights into blocking and SPV dynamics as a framework to evaluate possible linkages between AA and NH midlatitude severe winter weather. 

About Edward Hanna

Edward Hanna is Professor of Climate Science and Meteorology in the College of Science, University of Lincoln, UK, and currently leads multi-institute research programmes into Greenland climate and ice sheet changes and North Atlantic atmospheric jet-stream variability. He serves as Co-Chair of the World Climate Research Programme Climate & Cryosphere (WCRP CliC) project's Scientific Steering Group, and is the WCRP representative on the Ice Sheet Mass Balance and Sea Level (ISMASS) expert group, as well as co-leading an Arctic-midlatitude climate linkages activity that is jointly sponsored by CliC and the International Arctic Science Committee.

Edward has published >150 research papers in international peer-reviewed journals, including several papers in Nature journals and in Science. Together his papers have attracted >19,900 citations (H index 65) according to Google Scholar. Prof. Hanna has led an international team to reconstruct Greenland Ice Sheet surface mass balance, the results of which have been used by the Intergovernmental Panel on Climate Change, on which he was a Contributing Author on their Fifth Assessment Report. Edward has developed the concept of the Greenland Blocking Index related to North Atlantic polar jet stream changes, as a key driver of the recently increased Greenland ice melt.