Mat Collins of Exeter University clarified to the world a week ago that the direct cause of the UK's wet and windy winter was/is the North Atlantic Jet Stream. It has been directly responsible for the 'conveyor belt' of powerful storms which have hit the UK, one after another, in seemingly endless succession, since December 2013 all the way into February of this year. The rain precipitated by those storms has resulted in widespread river flooding.
In addition, a particularly deep depression which coincided with a very high tide on the 5th/6th December also resulted in fairly severe coastal flooding along eastern coastal areas. Nothing as bad as the devastating tidal surge of 1953 but that was more down to massively improved flood defences in the last 50 years. The Dec 2013 tidal surge was probably only a shade less menacing in terms of actual sea level rise than was the 1953 event. Severe gales and storm force winds have also driven huge waves over sea defences in Wales and the West Country, resulting in yet more localised flooding.
All this chaos due to the Jet Stream, due to the run of extreme weather caused by that Jet Stream. But, given the exhaustive news coverage and the opportunity for a propaganda coup, it was inevitable that the proponents of CO2 induced global warming would figure out some way to link in the storms with 'climate change' and, right on cue, up stepped Julia Slingo to claim that 'all the evidence' pointed to a link between the UK floods and 'climate change'.
It turns out that what she really meant was that there was moderate confidence in climatological circles that a warmer world would result in a more humid atmosphere and hence increased frequency and intensity of downpours. Not at all comparable to increased storminess, especially in winter, but the effect was immediate and very favourable - the warmist press and politicians leapt on the bandwagon to claim that this winter was due to global warming. Scientific proof not needed, only the word of the Met Office chief scientist.
It has become increasingly apparent that the Jet Streams are implicated in the patterns of extreme weather which we seem to be increasingly seeing across the globe. There are four altogether, two in each hemisphere, the stronger polar jet streams and the weaker subtropical jet streams, each marking the boundaries between major air masses.
For example, it was a deep 'meander' in the Northern Hemisphere polar jet stream which created the 'blocking' conditions responsible for the Alaskan heatwave last year. Similarly, the 'washout summer' of 2012 here in the UK was caused by an abnormally southerly trending jet stream, again driving Atlantic storms over the British Isles, but this time during summer. The meandering jet stream over the USA this winter has allowed polar air to push far into the continent, giving Americans an exceptionally cold winter. Last winter (2012/13), the UK experienced a very cold late winter/early spring due to the jet stream moving way down south, missing the UK altogether and allowing the ingress of cold polar air and that memorable run of savage east/north-easterlies. A 'normal' UK winter would have the jet stream sitting generally a little further north, across Scotland. This winter it has been 'stuck' over southern Britain and has been abnormally strong.
With global mean temperatures static for 17 years but extreme weather seemingly on the rise linked to a changing jet stream, it is hardly a surprise that the man-made climate change advocates are looking to associate these changes with global warming. Hence Jennifer Francis at Rutgers University now postulates that a warming Arctic has 'slowed' the polar jet stream and made it meander more, much like a river meanders when it loses kinetic energy on the gently sloping flood plains way downstream of its upland source.
The speed of the jet stream is driven primarily by the temperature difference between the polar and subtropical air masses. If Arctic air is warmer due to accelerated warming in the polar regions because of global warming, the theory is that the difference in temperature between polar and subtropical air will be less. Thus the jet stream will slow and start to meander more, producing the 'loops' which have been responsible for weather getting 'stuck' in various locations, producing localised droughts or deluges, heatwaves or extreme cold spells.
The theory is tentative and Francis admits that there are uncertainties, but it does illustrate that alarmists are starting to line up in order to link jet stream changes (and hence patterns of extreme weather) with AGW. Trying to explain this year's flooding in the UK using such a theory runs into a big problem however - the jet stream may be meandering, but it has actually increased in speed over the North Atlantic, hence the ferocity and persistence of the storms which it has spawned and driven to our shores.
This belies the somewhat simplistic theory which equates a slower moving jet stream with a more meandering one and a faster jet stream with a much straighter course. Also, in a warmer world, climate models predict the jet streams will move polewards, just as they do during summer each year due to increased solar insolation, sinking southwards again during the winter months. This appears not to be happening.
Which rather neatly brings us to explanations for jet stream changes based upon solar activity, not seasonal changes in insolation but longer term changes over the 11 year solar cycle and beyond, plus - and this winter being a particular case in point - very brief changes marked by sudden bursts of increasing sunspot activity (solar flares and coronal mass ejections - CMEs). For it may be no coincidence that this winter has seen the Sun burst into life in what has otherwise been a remarkably subdued solar cycle, so remarkably subdued in fact that scientists are predicting a Grand Solar Minimum, at least as severe as the Dalton minimum, possibly even as pronounced as the Maunder minimum, which coincided with the coldest period of the Little Ice Age.
What we need to investigate, especially as far as this winter is concerned, is a link between solar activity and the character of the jet stream which might lead to increased extreme weather/storminess. Stephen Wilde, in his New Climate Model, equates a more active sun with a 'tighter', faster, more northerly tracking jet stream; conversely, a less active sun with a slower, more meandering, southerly trending stream. We seem to be at the stage of the latter now, where the general decrease in solar activity has rendered the jet stream more 'sluggish'.
But bursts of solar activity within the envelope of a generally less active period of solar activity seem to have energised this 'sluggish', meandering jet stream, not enough to push it northwards and straighten it out, but enough to make it move faster, at least along certain sections. Hence we have the storms which have slammed into the British Isles this winter.
The mechanism whereby increased/decreased solar activity affects the jet stream is not totally clear. Total solar irradiance (TSI) varies little but there are increasing numbers of scientific papers suggesting amplification mechanisms. Stephen Wilde states: "The cause [of change in position and behaviour of the jet stream] appears not to be raw solar power output (TSI) which varies
too little but instead, the precise mix of particles and wavelengths
from the sun which varies more greatly and affects ozone amounts above
the tropopause". Svensmark of course postulated that periods of decreased solar magnetic activity allowed greater influx of galactic cosmic rays (GCRs) which he correlated with increased cloudiness leading to global cooling, and vice versa.
It might be worth noting that, apparently independently, earth's own geomagnetic field has weakened considerably over the last 100 years or so, possibly as a precursor to a complete geomagnetic field reversal. We can expect the geomagnetic field to weaken further in the coming years, allowing even more GCMs plus radiation from our sun to penetrate our atmosphere, affecting our climate in ways which may be hard to predict.
Coming back to solar activity and the effect it has had on this winter, particularly here and in the US, Tallbloke's TalkShop has a timely contribution from Polish contributor 'ren', which seeks, with somewhat limited clarity unfortunately, to explain why the polar vortex 'locked'. He says:
"In October 2013 there was a decrease in solar activity, as evidenced by the growth of cosmic rays at that time. This decline resulted in a short-term rise in temperature in the stratosphere, the ozone zone. . . . . . . . . . . Smaller solar activity means an increase of ionizing radiation over
the Arctic Circle, which in turn affects the reactions taking place in
the area of the ozone over the Arctic Circle. As is known the
temperature drops in the troposphere and the stratosphere borders later
grow depending on the amount of ozone formed in the ozone zone.
These seemingly small changes in the stratosphere were the beginning
of the lock polar vortex, which lasts all winter and causes influx of
polar air over North America and warm, with short breaks over Europe."
A comment from Stephen Wilde on this Tallbloke post is as follows:
"“This decline (in solar activity) resulted in a short-term rise in temperature in the stratosphere, the ozone zone.”
Yes, this is what I’ve been telling everyone for several years.
A quiet sun is supposed to REDUCE ozone and lead to COOLING of the
stratosphere and I think that is right above the equator but not right
above the poles."
Which only serves to confuse me further!
Another timely post on Tallbloke provides reference to a science paper which purports to show that the sun has distinct 'modes' of activity. I quote:
"Conclusions. The Sun is shown to operate in distinct modes – a main
general mode, a Grand minimum mode corresponding to an inactive Sun, and
a possible Grand maximum mode corresponding to an unusually active Sun.
These results provide important constraints for both dynamo models of
Sun-like stars and investigations of possible solar influence on Earth’s
This is important in that it demonstrates that the Sun behaves differently in these 2 (or possibly 3) modes and that variations in solar activity, increases or decreases, may not have exactly the same effect upon our climate and the general circulation, the specific effect being dependent upon what mode the Sun is in at the time. So, for instance, bursts of activity during a Grand Minimum may affect the jet stream differently than they would say when the sun is in main general mode. Likewise, quiescence during a Grand Maximum may be different in character than very quiet periods which occur during a Grand Minimum.
There is well documented evidence that the Little Ice Age, besides being considerably cooler, was also a particularly stormy period, especially in Northern Europe. The Great Storm of 1703 occurred on 26 November 1703 and remains the most violent and destructive storm ever to hit Southern England and the Channel. Virtually every ship in the English Channel was sunk on that fateful day, with the loss of 8000-10000 lives. Historical records abound which testify to its ferocity, seemingly unmatched before and certainly since. Even October 1987 paled in comparison.
What is fascinating is that 1703, in particular late 1703, marked an end to a very long period (from about 1645) during the Maunder minimum when virtually no sunspots were observed at all on the face of the Sun. A minor maximum of solar activity occurred in late 1703/early 1704 as shown here:
The graph was taken from this paper entitled 'The Revival of Solar Activity after Maunder Minimum in Reports and Observations of E. Manfredi'. The authors state:
"We have found in our archives a very great number of references to sunspots in the years 1703 to 1707."
So, 1703 marks a very important year in the revival of solar activity after the very pronounced Maunder Minimum, and indeed, we can see this revival on the record of sunspot activity stretching back 400 years from 2000:
It's the small red peak visible just after 1700. Insignificant one might feel against the backdrop of the much greater activity in the centuries which followed. But is it any coincidence that, at almost exactly the time when the Sun first first burst into life after decades of inactivity, the monster storm of 1703 hit our shores?
In summary then, the jet streams, in particular the faster, more powerful mid-high latitude polar jet streams, drive our patterns of weather. When they are in 'meander' mode, they can produce prolonged spells of severe weather, be it droughts, heatwaves, severe floods or bitingly prolonged cold. They shift north or south according to the seasons. An energised North Atlantic jet stream has been responsible for the remarkable run of UK storms this winter and the resultant flooding.
The race is on to discover what drives the jet streams and determines their character, whether 'sluggish' and meandering or faster moving and straighter. The CO2 warmists obviously have a vested interest in proving that global warming is responsible for the current jet stream anomalies, because then they can 'prove' that severe weather really is down to 'climate change' - rather, that is, than just stating it without any scientific evidence whatsoever.
For my money, there is far greater evidence and a lot more research in the literature which demonstrates that solar activity drives the jet streams - the exact manner and the specific physical mechanisms involved still yet to be pinpointed exactly, but we're getting there, fairly rapidly now.