The  crucial effect of jet stream position on the  climate forcing effect of persistent spreading aircraft contrails and contrail cirrus based on daytime  temperatures in Bangor, North Wales during  2006,2007 and 2013, by Dr Chris Barnes, Manager, Bangor Scientific and Educational Consultants, July 2013.

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The effect of jet stream position on the climate forcing effect of persistent spreading aircraft contrails and ensuing contrail cirrus based on simple observation of maximum daytime temperatures in Bangor, Wales during summer months of 2006, 2007 and 2013 is evaluated.  It is found that flying at night always causes positive forcing irrespective of the jet stream, although the positive forcing with a normal summer jet stream position to the north of the British Isles us minimal. Flying in the daytime with the jet stream in this position may cause very slight cooling but the statistical relevance is not concrete.  In the case of jet stream which has been displaced equator ward thus hitting the British Isles broadside from a Westerly direction, the climate effect of persistent contrails and ensuing cirrus appears to be far more serious. Possible explanations for these differences are proposed.   Based on the results, the possible use of jet aircraft as a means of local weather control is discussed.  Perhaps as expected, the presence of low to medium level cloud cover with or without coincident precipitation has a far more dramatic negative forcing effect. Ship tracks are already known to modify/create such cloud and use of ships as a mode of climate mitigation is also discussed. At least over Britain,   ships and some air flights may already be off-setting all potential CO2 warming. In North Wales, however, climate and other anthropogenic changes such as use of renewable energy technology are bringing major changes to hydrology and this will be discussed elsewhere.  Finally, arguments against stratospheric engineering are advanced based on disruption of the global electric circuit and catastrophic    atmosphere/lithosphere interactions. 




There is concern that growing International air traffic emissions and contrails may be a major player in global climate change (1).   Indeed some including the present author have suggested that contrails in various guises could be the major player in climate change (2, 3) even outstripping the positive forcing effect of CO2.


Under certain conditions however, and when laid down at certain times of day, persistent contrails might also cause a cooling effect (2,3).   


The present author has also previously established two distinct weather cycles associated with contrails and has suggested that their behaviour might be due to the type of natural or anthropogenic aerosol nucleation particles entrained.  There has been much conflict and uncertainty in the scientific literature regarding effects of persistent contrails and their attendant cirrus formations.  For an adjunct to the aerosol entrainment hypothesis it is instructive to look at the effect of jet streams.  De Grand et al (2000) (4)  reach the conclusion that climate forcing of contrail outbreaks in the troposphere is always positive and weak based on the fact that contrail outbreaks are more likely in association with jet streams, cyclone waves and frontal systems.         


More recently, Irvine et al (2013) (5) ,studying New York to London flights, have realised that not only the probability of contrails persisting is influenced by climatic conditions but also is the climatic impact of every single flight.  They have also noted that the climate impact of winter flights is greater because stratospheric contrails occur.  They have also noted that the climate impact of westbound flights appears greater than that of Eastbound flights.  The present author asserts that this is because many westbound flights are at night.   Irvine et al also remark that the CO2 impact of Eastbound flights is weakest when there is a strong jet stream tilted 'north eastwards' towards the UK.


There has been much talk recently about the North Atlantic Jet Stream being displaced and often too far Southwards, particularly in   the summer months. In the UK such displacement brings cool, more winter-like temperatures and excessive conveyor belt driven rainfall.  Jet stream positions are thought to depend on a range of complex variables such as the NAO, El Nińo, solar cycles, volcanic eruptions  etc. (6-12).  Some have even speculated they may be just the subject of random walk (13, 14).  Others have suggested that CO2 driven climate change is moving Atlantic jet streams in a pole ward manner (15, 16).  Except in the month of September this does not seem to have been borne out in the UK in recent years.     If jet streams respond  to stratospheric injection as a result of volcanic eruptions than maybe also they are starting to respond to anthropogenic aerosol.  Thus in terms of the climate forcing of aircraft and their contrails this opens up the possibility for yet another unconsidered feedback mechanism.   Some have said jet streams may also link to modulations of geo-physical phenomena via the ionosphere (17), so perhaps we should not even rules out possibly influence of World Power Grids and ionosphere heaters such as HAARP and SURA.  Even the influence of turbulence from wind farms should not be ruled out (18). 


In July 2006 and for some reason again in July (2013) the North Atlantic Jet stream has been in a far more stable and natural summertime position tilting North Eastwards over Iceland  and remaining generally well to the North of the British  Isles.  


Based on the above, the present author viewed this as an ideal time to make a study of the   effect of jet stream position on the climate forcing effect of persistent spreading aircraft contrails and contrail cirrus based on daytime temperatures in his home city of Bangor, Wales.  Given that persistent and spreading contrail outbreaks are often 100km wide there is some potential relevance for more of Wales or even parts of the British Isles as a whole.  


Details of the Study 

The study has been designed to make a comparison of the climate forcing effects of persistent contrails and ensuing cirrus by comparing sets of daytime temperatures in consecutive Summer months with and without a displaced jet stream and in the same summer month   with a normal and an equator ward displaced jet stream.  


In July 2007 the 300mb jet stream was displaced towards the equator resulting in almost unprecedented summer rainfall and flooding in the UK.  In much of the period between July 2007 and July 2013 the jet stream has been too far south resulting in a lot of summer flooding and resulting in three very cold winters. In July 2006 and in July 2013 the jet stream was in a more normal position to the North of the UK.  For much of June 2013 ( 6th -22nd ) the jet stream was also  displaced to the South.  Indeed since the 1970's the jet stream has often been displaced.  Dr Peter Stott, a leading climate scientist at the UK Met Office, states that since the 1970s the amount of moisture in the atmosphere over the oceans has risen by 4%, a potentially important factor.  Other possibly significant changes in the 1970's were; vastly increased jet aviation, the first ionosphere heaters also transmitted.  Following this, there have certainly been recent and abrupt changes in the monthly distribution of regional weather types in the British Isles. Such changes are thought by some to have began abruptly in 1981, see Mayes (19, 20).  Other potentially significant anthropogenic changes  potentially influencing the jet stream were: the first wide bodied high bypass turbofan aircraft were introduced in the 1980’s. (21)      The Sura Ionospheric heating facility also commenced operations about this time (22).

The study will make a comparison of the data from the three Julys and from June 2013. In more detail the method involves calculating the   average temperature for four separate conditions with the exception of July 2007 where shortage of data led to only three of the conditions being met.   The four conditions are peak daily temperature data has been acquired from within those periods and averaged for:


1.      Sunny days with no persistent contrails or contrail linked cirrus.

2.      Sunny days with persistent contrails and linked cirrus.

3.      Next 24h  after significant night time ( 7pm+) persistent contrail outbreaks *

4.      Days with overcast and /or rain.


Assumptions made in the study

The main assumption made is that flight numbers average out. The Bangor location is almost under a major E/W flight path and reference to the website flightradar24 suggests this to be a valid assumption. The other assumption made is that there is sufficient homogeneity of atmosphere and temperature not to worry too much about the precise location of each patch of persisting contrail or ensuing cirrus.  For certain solar zenith angles this may not be a valid assumption.  Weather and climate are naturally variable and random for this reason large standard deviations in the temperature data are unavoidable and are, indeed, to be expected.  


Results and Discussion

The results in which ‘JS’ stands for jet stream and ‘Cons’ stands for the presence of persistent, usually spreading, contrails  are tabulated below :


The results for July 2006 and 2013 (listed as 'summer 2006 and 2013' respectively in the table) with a normal summertime jet stream are remarkably similar.   Based simply on average daytime maximum temperatures it would appear that persistent contrails have statistically very little effect if the jet stream is well north of the UK

If anything persistent contrails which break out in the morning cause a very slight cooling effect whereas the days after evening contrail outbreaks are marginally warmer, presumably due to heat trapping and reduction of daily temperature range. 


On the other hand when the jet stream is displaced to the south so it strikes the UK   directly the results (listed as summer 2007 (July 2007) and summer 2013 (part of June 2013) in the table)   show a very different outcome, with significant warming or positive forcing in both cases with an average of .38C warming by day and a very significant 2.45C of warming on days following evening persistent contrail outbreaks.


The data in the table also shows another perhaps obvious, yet nevertheless, striking feature. That is the temperature reducing effect of medium and low level cloud or overcast whether or not associated with frontal precipitation. This is more pronounced and statistically more relevant when the jet stream is displaced to the south relative to its normal summertime position.  There has been talk of engineering the climate by stratospheric injection.  From these results, it would appear that quite simply low level cloud creation would have a far more dramatic and stabilisation effect.   Ship tracks modify marine stratus and indeed produce just this effect.  They may be indeed be offsetting virtually all CO2 warming. The crucial paper is that of Eyring et al 2010 (23).     


There has been much talk of how to mitigate the climatic effects of air travel.  The above results should significantly inform this process.   It has already been suggested that moving flight times from night to day could significantly reduce global warming (24). This present study strongly supports that notion.   However, when the jet stream is displaced, use of contrail avoidance algorithms is also advised.  Also there may be efforts directed at changing aircraft fuel or modifying exhaust emissions to maximise ice crystal size and morphology which brings about cooling rather than heating. The present author feels this ought to be possible without resorting to potentially dangerous climate mitigation schemes such as direct stratospheric injection and ocean seeding.         


To re-iterate, the findings, perhaps somewhat surprisingly suggest that at least over North Wales contrail outbreaks which occur when there is a normal summer jet stream pattern produce rather insignificant changes. Further work would be necessary to determine the overall statistical significant of the weak daytime cooling observed.   


There are several possible mechanisms which might explain the difference in the climate forcing behaviour of persistent contrails and  ensuing cirrus under these two very distinct jet stream conditions. Firstly there will be significantly different wind shear under the two conditions perhaps leading to different ice crystal configurations which are known to favour positive or negative forcing see the crucially important paper of Zhang et al (1999)  (25), secondly there will be different mixing of gases in the UTLS and, finally, there will be different aerosol nucleation particle entrainments.  For example, aircraft travelling on the West East Atlantic route often fly in a favourable jet stream to conserve fuel.  A displaced jet stream shortens the route and it is expected that under these conditions over North West Wales there will be always be significantly enhanced CO2, sulphate, ammonia and soot present in an   almost continuously replenished transport stream.    This alone may be sufficient to explain why there is so much extra positive forcing with the displaced jet stream.


Contrails as a means for local weather control. 

These findings prove beyond doubt that contrails have an inadvertent effect on weather and climate and hence it is further  proposed by the present author   that contrails could be employed as a means of local weather control either as an alternative to or as an adjunct to traditional seeding methods.   Interestingly, this point of view was first put forward by Murcray as early as 1970 (26).


A displaced jet stream can cause significant cold weather and snow precipitation disruption in winter and spring.  It is anticipated that contrail  engineering could be used to cause significance local warming as required  to mitigate snow fall and/or perhaps to change ice crystal shape/ size and/or hydrological distribution because contrails are known to scavenge moisture from other clouds and could be used to reduce precipitation n certain areas and enhance it in others.  



Climate control / Geo-engineering for the future

Whether we like it or not aviation has been inadvertently geo-engineering our climate at least since the dawn of the jet era.  The present author is sincerely of the opinion that appropriate use of aircraft and ships, particularly the latter, ought to be able to mitigate CO2 induced climate change well into the future. Clearly, we should still strive to become carbon neutral because of the ocean acidification and air quality degradation caused by the mitigating aerosols. These routes are however probably far more preferable than injecting other hitherto untested materials into the stratosphere and/or oceans.  For example, stratospheric injection as proposed by some, for example, Crutzen (2006) (27)  as supported by Mac Cracken (2006) (28)   could have catastrophic effects on the electrical properties of the atmospheric medium, see Beig 2008 (29).  Since the atmosphere and lithosphere are coupled via the earth’s global electric circuit (ref) the present author has very serious reservations against stratospheric injection in particular.  Of cause some inadvertent injection occurs at the UTLS due to normal flying and some natural injection due to volcanic action but surely we should not upset this sensitive balance any further?            




1.      Chapman 2007

2.      Barnes 2012

3.      Olivier Boucher

4.      J.Q. de Grand et al;2

5.      E.A. Irvine et al

6.      Woolings (2010)

7.      Price et al (1998)

8.      Tinsley (1988)

9.      Stuiver et al ( 1995)

10.  Tinsley (1989)

11.   Zanchetin et al (2011)

12.  Stenchikov et al (2006)

13.  Woolings et al (2013)

14.   Frame et al ( 2013)

15.  Kidston and Vallis (2011)

16.  Riviere (2011)

17.  Waldock and Jones (1987)


19.  Mayes (1994)

20.  Mayes (1995)



23.  Veronica Eyring et al (2010)



26.  Zhang et al (1999) ( link to Murcray 1970)

27.  Cutzen (2006)


29.  Gulfrain Beig (2008)