Is Arctic warming influencing the UK’s extreme weather?

Is Arctic warming influencing the UK’s extreme weather?

SOURCE: University of Lincoln DATE: January 4, 2018 SNIP: Severe snowy weather in winter or extreme rains in summer in the UK might be influenced by warming trends in the Arctic, according to new findings. Climate scientists from the UK and the US examined historic data of extreme weather events in the UK over the past decade and compared them with the position of the North Atlantic polar atmospheric jet steam using a measure called the North Atlantic Oscillation (NAO) index. The NAO indicates the position of the jet stream – which is a giant current of air that broadly flows eastwards over mid-latitude regions around the globe – through a diagram which shows ‘negative’and ‘positive’ spikes, similar to how a heart monitor looks. The researchers highlight that the exceptionally wet UK summers of 2007 and 2012 had notably negative readings of the NAO, as did the cold, snowy winters of 2009/2010 and 2010/2011, while the exceptionally mild, wet, stormy winters experienced in 2013/2014 and 2015/2016 showed pronounced positive spikes. The scientists also highlighted a correlation between the jet stream’s altered path over the past decade – so-called jet stream ‘waviness’ – and an increase during summer months in a phenomenon called Greenland high-pressure blocking, which represents areas of high pressure that remain nearly stationary over the Greenland region and distort the usual progression of storms across the North Atlantic. Increased jet waviness is associated with a weakening of the jet stream, and the accompanying ‘blocking’ is linked to some of the most extreme UK seasonal weather events experienced over the past decade. The strength and path of the...
Stunning new analysis reveals just how unprecedented Harvey was

Stunning new analysis reveals just how unprecedented Harvey was

SOURCE: Think Progress DATE: September 14, 2017 SNIP: Hurricane Harvey’s landfall in Texas was “unprecedented” and “beyond anything experienced,” as the National Weather Service described it late last month. Now scientists are beginning to quantify just how unprecedented it was. A study released Friday by Metstat, a weather-analysis company specializing in “detailed precipitation analysis” and “weather frequency analysis,” found that Harvey delivered a stunning once-in-25,000-year deluge over much of southeast Texas. Some places saw an unimaginable once-in-500,000-year deluge, which translates to a 0.0002 percent chance of this deluge occurring in any given year. Since global warming has been making extreme precipitation events more likely, however, the U.S. won’t have to wait 25,000 years to witness the next event of Harvey’s proportion. As climatologist Michael Mann explained during the storm, “the kind of stalled weather pattern that is drenching Houston is precisely the sort of pattern we expect because of climate change.” Climate science predicted a weaker jet stream, and Harvey stalled because of a weakened jet...
Climate change: ‘human fingerprint’ found on global extreme weather

Climate change: ‘human fingerprint’ found on global extreme weather

SOURCE: The Guardian DATE: March 27, 2017 SNIP: The fingerprint of human-caused climate change has been found on heatwaves, droughts and floods across the world, according to scientists. The discovery indicates that the impacts of global warming are already being felt by society and adds further urgency to the need to cut carbon emissions. A key factor is the fast-melting Arctic, which is now strongly linked to extreme weather across Europe, Asia and north America. The new work analysed a type of extreme weather event known to be caused by changes in “planetary waves” – such as California’s ongoing record drought, and recent heatwaves in the US and Russia, as well as severe floods in Pakistan in 2010. Planetary waves are a pattern of winds, of which the jet stream is a part, that encircle the northern hemisphere in lines that undulate from the tropics to the poles. Normally, the whole wave moves eastwards but, under certain temperature conditions, the wave can halt its movement. This leaves whole regions under the same weather for extended periods, which can turn hot spells into heatwaves and wet weather into floods. This type of extreme weather event is known to have increased in recent decades. But the new research used observations and climate models to show that the chances of the conditions needed to halt the planetary waves occurring are significantly more likely as a result of global warming. Recent changes in the Arctic are particularly striking, with record low levels of ice cover and extremely unusual high temperatures. “Things in the Arctic are happening much faster than we expected,” said Prof...