The recent warming trends in the Arctic may be linked to the increase in severe snowy weather in winter – as well as extreme rains in the summer – in the UK, according to a new study.
Climate scientists from the UK and the US analyzed data from extreme weather events over the last decade in the UK, and compared them with the position of the North Atlantic polar atmospheric jet stream using the North Atlantic Oscillation (NAO). The NAO is a measurement that indicates the position of the jet stream through a diagram that shows negative and positive spikes – similar to a heart monitor. The jet stream is an enormous current of air that flows east over mid-latitude regions around the planet.
During the extremely wet summers of 2007 and 2012 in the UK, the researchers found significantly negative readings of the NAO. These same readings showed up during the cold, snowy winters of 2009/2010 and 2010/2011. On the other hand, during the mild, wet, stormy UK winters of 2014/2014 and 2015/2016, the NAO showed notably positive spikes.
Furthermore, the researchers noted a correlation between the jet stream’s altered path during the past decade – known as jet stream ‘waviness’ – and an increase in Greenland high-pressure blocking, which is a phenomenon during the summer months that represents areas of high pressure that remain stationary over the Greenland region. These high-pressure areas distort the usual progression of storms across the North Atlantic.
An increase in jet waviness is linked to a weakening of the jet stream, and the ‘blocking’ is associated with some of the most extreme UK seasonal weather events that have been experienced over the last decade.
It appears that increasing temperatures in the Arctic are influencing both the strength and path of the North Atlantic jet stream and the Greenland block phenomena. This suggests that these changes may be a major factor in the extreme weather conditions that the UK has experienced.
“In winter, a positive North Atlantic Oscillation (NAO) is linked with a more northward, vigorous jet and mild, wet, stormy weather over the UK, while a negative NAO tends to be associated with a more southerly-positioned jet and relatively cold and dry but sometimes snowy conditions,” says Edward Hanna, a professor of climate science and meteorology at the University of Lincoln’s School of Geography and an author of the study. “In summer the jet stream is displaced further north, so a positive NAO is typically associated with warm dry weather, while a negative NAO often corresponds to wetter, cooler UK weather conditions.”
Hanna assures that while weather in the UK is infamously variable, globally there has been a recent increase in high temperatures and heavy precipitation. The trend in the last decade has resulted in multiple record negative and positive December values of the NAO. While scientists are continuing to keep an eye on this, it’s clear that Arctic warming is having an influence on weather in more places than just the Arctic.