Is Arctic Warming Influencing UK’s Extreme Weather?
By Paul Homewood
WUWT covered this story last week:
From the UNIVERSITY OF LINCOLN, where they are trying to make the North Atlantic Oscillation bend to their will part of climate change.
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 North Atlantic jet stream and the Greenland blocking phenomena appear to be influenced by increasing temperatures in the Arctic which have averaged at least twice the global warming rate over the past two decades, suggesting that those marked changes may be a key factor affecting extreme weather conditions over the UK, although an Arctic connection may not occur each year.
Edward Hanna, Professor of Climate Science and Meteorology at the University of Lincoln’s School of Geography, carried out the study with Dr Richard Hall, also from the University of Lincoln, and Professor James E Overland from the US National Oceanographic & Atmospheric Administration Pacific Marine Environmental Laboratory.
Professor Hanna said:
“Arctic warming may be driving recent North Atlantic atmospheric circulation changes that are linked to some of the most extreme weather events in the UK over the last decade.
“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. 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.
“While part of the uneven seasonal North Atlantic Oscillation changes might be due to natural random fluctuations in atmospheric circulation, the statistically highly unusual clustering of extreme NAO values in early winter, as well as extreme high summer Greenland Blocking Index values since 2000, suggest a more sustained, systematic change in the North Atlantic atmospheric circulation that may be influenced by longer-term external factors. This includes possible influences from the tropical oceans and solar energy changes as well as the extreme warming that has recently occurred in the Arctic.
“Of course, weather is naturally chaotic, and extremes are a normal part of our highly variable UK climate, but globally there has recently been an increase in the incidence of high temperature and heavy precipitation extremes. The cold UK winter episodes we noted are not so intuitively linked to global climate change but reflect part of a long-term trend towards more variable North Atlantic atmospheric circulation from year to year during winter months, especially early winter.
“This trend has culminated in the last decade having several record negative and positive December values of the North Atlantic Oscillation, with lots of resulting disruption from extreme weather over the UK. On the other hand there has been no really notably dry, hot, sunny summer in the UK since 2006; summers overall have either been around average or exceptionally wet, and this appears to be linked with strong warming and more frequent high pressure over Greenland in the last decade.”
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https://wattsupwiththat.com/2018/01/04/claim-arctic-warming-is-influencing-the-uks-extreme-weather/
Now that the Met Office has published the data for 2017, we can see what the facts tell us.
Wet Summers
First, summer rainfall.
Remember the claim is that:
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.
Summers overall have either been around average or exceptionally wet, and this appears to be linked with strong warming and more frequent high pressure over Greenland in the last decade.
However the data from the Met Office’s England & Wales Precipitation Series give us a totally different story.
Although there have been a couple of wet summers recently, there is absolutely nothing unusual at all about these, when looked at with a longer term perspective.
https://www.metoffice.gov.uk/hadobs/hadukp/data/download.html
Indeed, it is plain that wet summers were more common in the 19thC, tending to indicate that a colder Arctic, and correspondingly more southerly jet stream, leads to wetter summers. Not a warmer Arctic, as Hanna suggests.
The facts are even more stark when we look at extreme rainfall months:
https://www.metoffice.gov.uk/hadobs/hadukp/data/download.html
Plainly Hanna’s argument falls flat on its face as far as summer rainfall is concerned, but what about his other claim?
Wet Winters
Severe snowy weather in winter or extreme rains in summer in the UK might be influenced by warming trends in the Arctic.
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.
Yes, we have had two wet winters recently. But were they anything more than simple weather events?
https://www.metoffice.gov.uk/hadobs/hadukp/data/download.html
Obviously the winter of 2013/14 stands out, but even that weather was not unprecedented. Between November 1929 and January 1930, rainfall totalled 500mm, compared to 455mm in 2013/14.
Of course, November to January is not a season, but the exceptional rainfall then, a record for any three months on the Series, was no less remarkable for that.
[The paper puts a lot of emphasis on weather blocking. In that respect, it is worth noting that the extraordinarily wet weather in 1929/30 actually lasted for four months, not just three. Between October and January, precipitation totals were 624mm.
The wettest four month period in 2013/14 was much less, with 556mm from October to January]
Other than that standout winter of 2013/14, there has been nothing out of the ordinary in the last decade or two.
As for extreme months, the wettest winter months were in the 1860s and 70s, and later in the 1910s.
https://www.metoffice.gov.uk/hadobs/hadukp/data/download.html
So, as with summer rainfall, Hanna’s theory simply does not correlate with any of the very clearly known facts.
Cold Winters
Severe snowy weather in winter or extreme rains in summer in the UK might be influenced by warming trends in the Arctic.
The cold UK winter episodes we noted are not so intuitively linked to global climate change but reflect part of a long-term trend towards more variable North Atlantic atmospheric circulation from year to year during winter months, especially early winter.
According to the official Met Office data, however, there has been nothing remotely unusual about recent winters:
https://www.metoffice.gov.uk/climate/uk/summaries/actualmonthly
December 2010 was notoriously cold, as was the previous winter. However, as Julia Slingo confirmed in a report to Sir John Beddington at the time, neither episode was particularly unusual.
As for cold monthly extremes, again we find that they are not becoming more severe or more frequent.
https://www.metoffice.gov.uk/climate/uk/summaries/datasets
Final Thoughts
According to Hanna, “we need extended records over at least a further decade to more reliably attribute these changes to global warming”. (Translation – give us some more money!)
He needs no such thing. He already has two centuries of data which wreck his little theory.
Comments are closed.
NOT A LOT OF PEOPLE KNOW THAT 
“Arctic warming may be driving recent North Atlantic atmospheric circulation changes that are linked to some of the most extreme weather events in the UK over the last decade.”
key paragraph = prime BS.
I do aver that, the NAO is little understood and undoubtedly influences the north west shelf of the Eurasian continent, if also influences and interacts with the AO and we only know of that darkly, Arctic sea ice is more influenced by Oceanic forces rather than the atmospheric influence but the Sun and corriolis drives the lot of it.
There is no climate crisis in the Arctic, there is no man made owt – ‘warming the Arctic’ the Arctic ocean it’s climate influences do change however and anecdotal evidence – reports clearly demonstrate it, in that Arctic sea ice is always in flux, it retreats and refreezes – period.
Lincoln College of – University pretensions, needs to quieten down before people actually notice what it is, the backwater of inferior academia.
Indeed!
When I was young Professors and Doctors were held in awe and looked up to with enormous respect, as they the pathfinders of the 20thC cadre revealed their wondrous discoveries, mostly beneficial to mankind, and others less able toiled unsung and without acclaim to produce the fruits of these discoveries for practical use.
How disheartening it must be for those doing real science today to see these charlatans feted by politicians and press for papers and findings that are written in the conditional tense, whilst the reputation of science here in the real world increasingly lies in tatters.
I’ve never heard of the University of Lincoln before. I note that Chris Packham is a visiting professor – no need to say more.
What does he profess ?
verb
1.
claim, often falsely, that one has (a quality or feeling).
2.
affirm one’s faith in or allegiance to (a religion or set of beliefs).
https://dictionary.cambridge.org/dictionary/english/profess
https://www.collinsdictionary.com/dictionary/english/profess
Even in the 1960s there were many academics who were not worth their salaries: the large expansion of the universities has just added massive numbers of second-raters to the list of professors.
Peer review was a serious business until the 1980s, since when it has been cronyism in a rocketing number of pseudo-academic publications..
There is a global outbreak of mildness. Maximum temps are slightly down , minimums are just ever so slightly more up, producing ever so slightly increased averages. Terrifying, isn’t it?
One of the major problems we have is the (mis)use of so called anomalies. The whole conversation is based on these figments of imagination. So we get colourful global maps showing red bits which are supposed to scare us into thinking everything is hotter. A recent example is the red spots over Siberia which we are told ‘balance’ the deep blue bits over N America. Until the actual temperatures are uncovered, which show the Siberian red spots are actually MINUS 15C rather than some arbitrary 30 year average of minus 17C. So although most of the NH is minus degrees , the anomalies really tell us its getting warmer.
Its complete BS. Somehow the discussion needs to be forced back to talking about real temperatures, not some artificial anomalous anomalies.
Yes, but – if we show REAL temperatures, we’ll need to use VERY fine graph paper, otherwise it’ll come out as a flat line! /sarc
Is the warming in the Arctic real, measured and confirmed? Without that fact established it is all speculations in an invented theory.
There’s only a handful of measurements from land stations around the Arctic Circle, but most of the Arctic is just guessed at
“Is the warming in the Arctic real, measured and confirmed?”
No, no and no.
What Arctic warming?
Snow cover in the NH has shown no trend for well over two decades.
If the Arctic was warming you’d think snow would notice.
Paul
You have both the knowledge of and access to the relevant data and statistics to warrant a comment on the letter in todays Times (Global Cooling January 10th 2018). Even to my simple understanding 200 years in 50,000 is statistically unimportant.
Have you got a copy? The Times is behind a paywall