Arctic Amplification and mid-latitude extreme weather

Prof. Edward Hanna
School of Geography and Lincoln Centre for Water and Planetary Health, College of Science, University of Lincoln, UK
Seminar Date: 
29. August 2018 - 11:15 - 12:00
Lecture room, Ground Floor, NERSC

Recently there has been a significant increase in some types of extreme weather over the UK and other northern mid-latitudes: for example winters 2013/14 & 2015/16 in the UK were exceptionally mild, wet and stormy, while large parts of winters 2009/10 and 2010-11 were unusually cold and had record deep snows. Snowmageddon hit the eastern seaboard of the USA in the last few winters. Meanwhile several recent summers, most notably 2007 and 2012, experienced record UK rainfall and widespread flooding. These extreme events are closely related to recently-observed shifts in the eastward-moving atmospheric jet stream over the North Atlantic, where the jet has at times become slower moving with more north-south meanders exchanging air masses between mid- and high-latitudes. These changes may be partly driven by the major reduction in Arctic sea-ice cover and amplified warming that has occurred in high northern latitudes over the last decade. I will present new research results concerning recent changes in Arctic Amplification (AA) and jet-stream circulation/blocking changes. Although AA is just one of the factors affecting jet-stream changes, there is mounting evidence, partly from our work at Lincoln together with the Met Office and other research partners, that the state of the jet (speed and position) is inherently largely predictable 2 or 3 months in advance for both the summer and winter seasons. Global warming is not a uniform process - as seen through recent erratic temperature rises in the UK, Iceland and Greenland - and is prone to spring surprises through some subtle but high-impact changes in mid-latitude extreme weather.