Arctic – lower latitude coupling : What is the forcing and what is the response ?

1 R ecent Arctic changes are expected to, and may already be, impacting middle latitudes and the rest of the globe. For the first time, the US National Climate Assessment (Melillo et al. 2014) has called attention to a possible role of the Arctic in variations of the jet stream (now referred to as the “polar vortex”) over the contiguous United States (http://nca2014. globalchange.gov/report/our-changing-climate/melting-ice). As evidence of the increased public awareness of this topic, Hamilton and Lemcke-Stampone (2013) have recently reported results showing that a clear majority (60%) of surveyed members of the public now accepts that there is a connection between Arctic warming and mid-latitude weather. Yet the Arctic’s connection with middle latitudes represents a challenge to scientific diagnosis because the forcings and responses of the two regions are intertwined. Hence a key question about Arctic− lower latitude coupling is: What is the forcing and what is the response to Arctic warming?