Aviation more adequately accounts for global temperature change since 1940 then do earthbound CO2 concentrations, furthermore aviation  and ships account for recently stalled warming and new trend towards cooling by Dr Chris Barnes Bangor Scientific and Educational Consultants 

Dr Barnes' Homepage Link  http://drchrisbarnes.co.uk



Global temperature rise between 1940 and 2000 is shown to correlate far better with world air flight numbers than incremental earthbound carbon dioxide increase. Aircraft contrails have a much stronger climate forcing effect than carbon dioxide. However when contrails evolve into cirrus like cloud with appropriate ice crystal size, shape and distribution, particularly if daytime flights dominate there can be a net cooling effect. Shipping too induces an enormous cooling effect. Taking the air corridor which passes to the North of Bangor in Wales as an example, the author has noticed a predominance of this type of cloud evolution only over the last decade or so. When data up to 2011 is included global warming as a function of air flight numbers appears to have stalled. When a quadratic fit is applied a new trend of cooling is predicted.  It is thus proposed that this can be adequately explained by the switch from linear to spreading contrails and subsequent cirrus evolution.  It is further proposed that by adjusting ice crystal size and distribution a method of low cost geo-engineering should be feasible. Contrails and cirrus cloud can alter planetary hydrology budget and can also encourage the formation of low pressure systems or potentially alter the course of weather systems so    more research and a cautious approach will be essential. Aerosols injected by aircraft absorb UVB light and contrails reflectively scatter the same. UVB is essential for vitamin D synthesis and healthy living, additional caution will be needed here 


"Discovery consists in seeing what everyone else has seen and thinking what no one else has thought."

  --  Albert Szent-Gyorgoi Von Nagyrapolt



Over the past thirty years or so there has been considerable debate over global warming. In its heyday it was stated that 97% of climate scientists accepted global warming and doubtless most accepted that global warming was caused by anthropogenic greenhouse gas emissions particularly carbon dioxide.   However, greenhouse gases including Carbon Dioxide and others would be expected to mix by various diffusive processes throughout the planetary atmosphere yet most of global warming is observed in the Northern Hemisphere.  74.6% of the entire World’s air traffic is also in the Northern Hemisphere http://www.choike.org/documentos/tourism_help_poor.pdf. On the other hand cloud generated by aircraft, although having a residency half life significantly and orders of magnitude   less than that of C02, would be expected to remain more localised and is regularly replenished while ever aircraft remain in the skies. 

Thus to the present author it is blatantly obvious that here is a most obvious potential association between air traffic and global temperature change which has not been adequately investigated to date.    Very recently indeed the UK met office have released data from the Hadley Centre that appears to show that global warming is over or at least that there has been a sixteen year pause [1].  The work presented here below will very broadly support this but for hitherto unconsidered reasons. 


The present author is not a climate scientist by training but does have scientific training and is educated to a high level in both scientific and engineering disciplines. Further the present author has a number of international publications and patents and patent specifications. Further the present author has during the last decade or so been turning his attention to unexplained physical and environmental phenomena and has a number of internet publications on the same. The present author has also a keen interest in the weather and has local temperature and rainfall records going back to 1981.


Living in North Wales under a busy air corridor the present author has witnessed changes in the skies above and changes in the local climate on a previously unprecedented scale. At first sight these do not appear to be changes for the better.  The skies appear far cloudier, particularly with contrails and aviation cirrus and the mean temperatures have been falling significantly.    Indeed once could say that whole new families of hitherto rare or unseen cloud types have been spawned in recent times. The average member of the public who does not have an interest in natural science and who does not look up at the sky would, perhaps, not even notice these changes. Such displays are interesting in other senses as one can visualise AGW’S in real time.  One can also see the most phenomenal solar optical displays ranging from cloud edge iridescence in blue and orange or pink and green to sun dogs and full solar or lunar halos and circum-zenithal arcs.     Prior to the last decade such displays were extremely rare and might only be seen in Alaska and Northern Scandinavia.  These displays are associated with ice crystals usually at cirrus cloud heights.


The present author has noticed that almost all these phenomena appear to arise from aircraft contrails which often don’t dissipate but spread out into huge sheets with often the most spectacular   patterns. Ship tracks too cause similar patterns.  One can see evidence of wake vortex induced swirl in these patterns and sometimes evidence of Kelvin Helmholtz instability.  In other words text book type fluid dynamics type processes can be visualised in real time by a ground to sky observer!  From a cloud perspective you can see fall streaks, hole-punch effects and mammantous and scuds at times you would not normally expect. The author asks two questions if all these spectacular, perhaps local,   effects have developed as a result of aircraft in the last decade or so firstly, are such effects more widespread and secondly surely they will be having a profound effect on both weather and climate?  Indeed so concerned about these changes was the author that he placed an article in his local newspaper several years ago and also contacted a scientist at the UK Met Office.  He also recently took discussions with a leading climate scientist in the USA regarding the cooling he had noticed. He also took discussions with a contrail scientist and an optical physicist regarding the optical effect he had noticed. Persistent contrails are not entirely new. They were first noticed in WW2 but there sudden proliferation in all our skies since the turn of the millennium demands the application of some serious science.     


From the point of view of a lay person commonsense dictates that cloud ought to cool the planet by screening out the sun. The true picture is of course far more complicated than this and depends on both Long and Short Wave radiation effects; cloud optical depth, ice crystal or water droplet size and distribution etc.   


It is rewarding to see then that aviation science has at least now caught up with the personal observations of the author and indeed from a Google Scholar literature search it would appear there is presently intense research going on into the climate forcing effects of aircraft contrails.   The consensus of this research appears to be that linear and spreading contrails have a positive climate forcing effect i.e. they warm the planet,[2]     , however the paper goes on to say that possible changes could be made to aircraft to change this into a cooling effect. 


However, when contrails or aerosol form aircraft spread out to form cirrus like cloud, presumably the likes of which the present author has been observing the picture is far less straight forward.  Natural cirrus has a warming effect [3]

Some scientists have concluded that contrail cirrus has also a warming effect [4]  http://www.met.reading.ac.uk/~sgs02rpa/PAPERS/Haywood09JGR.pdf and [5] Atlas et al 2006  http://journals.ametsoc.org/doi/abs/10.1175/JAM2325.1.

However, for both persisting contrails and contrail cirrus when ice crystal size and its distribution is taken into account, a different picture emerges, see Zhang et al 1999 [6]  http://directory.umm.ac.id/Data%20Elmu/jurnal/A/Atmospheric%20Research/Vol52.Issue1-2.Aug1999/835.pdf.   See also Geerts and Linacre 2002 [7] which also refers to the cooling effect of ship tracks   http://www-das.uwyo.edu/~geerts/cwx/notes/chap08/contrail.html.

Whereas, some remain convinced that further studies will be necessary, Ramanthan 1987 [8]  http://www.agu.org/pubs/crossref/1987/JD092iD04p04075.shtml.

Finally, Sassen concludes contrail cirrus may cause cooling depending on such factors as day and night flights. Cooling is favoured by daytime flying. [9] http://cat.inist.fr/?aModele=afficheN&cpsidt=2828565. In this respect it should be noted that in Britain night flying is very limited which ought to support the Sassen model[10]  http://www.richmond.gov.uk/home/environment/pollution/noise_pollution/aircraft_noise/night_flights/current_limits_for_night_flights_at_heathrow-5.htm




Atmospheric Carbon dioxide levels are still increasing due to anthropogenic activity yet global warming has apparently stalled.  Either carbon dioxide is not responsible for global warning or another (feedback?) process or other processes are countering the increase due to carbon dioxide by themselves causing a cooling effect.  If carbon dioxide is not responsible for global warming in modern times then what is?  Based on the author’s observations it would seem logical to explore the once unseen possibility that a large proportion of or even possibly all of global temperature change might be due to aviation. The author does not regard his temperature data of sufficient quality to employ in the testing of this hypothesis so only internationally published data available in the public domain (Internet) will be employed. If air flights alone rather than anthropogenic CO2 are responsible for global warming then there should be a better correlation with the former. Furthermore in many parts of the World, including here in North Wales, spreading persistent contrails and contrail cirrus have only been noticed by observers on the ground for about that decade.  If these do in fact contribute to global dimming or global cooling as has been hypothesised by some above then this should be noticeable in say a plot of total number of air passengers versus temperature.   Indeed if there are only two major processes at work, one warming due to the contrails alone and one cooling due to the contrail cirrus or aerosol effects then this plot should fit a simple quadratic equation.  



The data sets used in this study are shown graphically below:





Figure 1 Aviation fuel use and emissions since 1940 courtesy of http://www.cate.mmu.ac.uk/research-themes/climate-change/impacts-of-aviation-on-the-climate/



Figure 2: Global Temperatures since 1860 courtesy of http://www.planetseed.com/relatedarticle/temperature-change-history





Figure 3 Linear regression plot 5 year average temperature from figure 2 against aviation fuel use from figure 1.

               ( period 1940-2000) 



Figure 4:  Linear regression plot 5 year average temperature from figure 2 against total anthropogenic CO2 emissions from figure 1.

                  (Period 1940 -2000)

Figure 5:  Linear regression plot 5 year average temperature from figure 2 against total aviation CO2 emissions from figure 1.

                  (Period 1940 -2000)




Figure 6:  Total revenue passenger kilometres since 1970 Courtesy of Money Week.com 



Figure 7 Linear regression   Global temp change Versus RPK 1970 -2000





Figure 8: Total World Air Passengers



Figure 9:  Global temperature change versus total number of air passengers (cumulative World data obtained from central source)    



Figure 10:  Global temperature change to 1970- 2011 versus passengers per annum quadratic fit


Discussion of the results

The results show unequivocally that in two of the modern times periods considered, namely 1940 -2000 and 1970-2000, aviation use correlates significantly better with global temperature change than total anthropogenic (mainly earthbound emissions) carbon dioxide does.  In the period 1940 – 2000, aviation use has been assessed using the only available data in terms of either fuel usage or aviation carbon dioxide emissions both of which will have some considerable bearing on contrail emissions.    For both cases the correlation with global temperature change is significantly higher R=.973 and .96 compared with R=.93 for total anthropogenic CO2.  One would perhaps expect a better correlation for fuel usage as it is other combustion products such as particulates and water vapour from the fuel which give rise to contrails.  This is an outstanding result especially given that aviation technology has changed over the period.  Long haul aviation technology changed less in the period 1970 -2000 and this is borne out by an excellent correlation between global temperature change and total passenger number in that period, with a regression factor  R= .993*.


Since 2000 many different types of contrails and contrail cirrus clouds have been seen by the present author in the skies over Bangor North Wales and in different parts of the UK. Shipping especially container shipping is also increasing significantly  and contributes toward new types of cloud formation due to salt spray. Likewise  contrails and new cloud types these are often seen by visitors to other countries or on television broadcasts or internet sites from other countries.      


  If one takes the view that a majority   proportion of these persisting contrails and contrail cirrus clouds  and ship tracks can create a cooling effect in line with the consensus of scientific publications then this should be directly observable in the climate data.  It is certainly observable in the author’s own data wherein his part of North Wales appears to be experiencing the coldest summers since his records began.  The only available point in the climate data is a point for 2011 indicating a rise of .52 Celsius with respect to the 1860 -2000 mean.  When this data point is fed into the above linear equation* together with the corresponding number of air passenger’s data point for the same year a significant deviation from linearity is noticed hence a slowing down in the warming rate is noticed. It is logical to suspect that the slowing down process was introduced sometime in the interim. In terms of a time period then perhaps anything as far as 13 years before the present and not that inconsistent form the recent claim of the UK met office [1].  If the total data from 1970-2011 is refitted to a quadratic equation a near perfect fit with a regression factor R=.998 is obtained.        It is instructive to use this fit as a predictive algorithm.  If aviation growth continues as forecast there will be 3.6 Billion air passengers annually in 2016. The algorithm predicts a continued cooling trend with a temperature only .44 Celsius higher than the mean.


 As an alternative or addition to the above it is possible that negative feedbacks associated with climate may also be relevant such as lapse rate and black body radiation.  In lapse rate, the atmosphere's temperature decreases with height in the troposphere. Since emission of infrared radiation varies with temperature, longwave radiation escaping to space from the relatively cold upper atmosphere is less than that emitted toward the ground from the lower atmosphere. Thus, the strength of the greenhouse effect depends on the atmosphere's rate of temperature decrease with height. Both theory and climate models indicate that global warming will reduce the rate of temperature decrease with height, producing a negative lapse rate feedback that weakens the greenhouse effect. Measurements of the rate of temperature change with height are very sensitive to small errors in observations, making it difficult to establish whether the models agree with observations.  With black body radiation, as the temperature of a black body increases, the emission of infrared radiation back into space increases with the fourth power of its absolute temperature according to Stefan–Boltzmann law. This increases the amount of outgoing radiation as the Earth warms. The impact of this negative feedback effect is included in global climate models summarized by the IPCC.  What will not be very relevant or what will only be of second order consequence will be Carbon Dioxide negative feedback effects as this present work has shown that CO2 is not the main driver of global temperature change.    


It cannot be stressed that for the observant sky watcher the hereinabove referred changes in contrails have been very dramatic.  Possibly because of this, a growing number of individuals world-wide have subscribed to some sort of a Conspiracy theory known loosely as ‘Chemtrails’ whereby they have believed that a number of  chemical additives have been added to aircraft contrails or sprayed out by aircraft with various goals such as climate and weather modification in mind. Such hypotheses are perhaps not that wildly fanciful, given for instance that there are obviously a huge number of published patents for both cloud seeding methodologies and contrail modification, both enhancement and suppression http://www.geoengineeringwatch.org/an-exaustive-list-of-patents/ [11].  Even without the need to invoke anything sinister, clearly a chance change in aircraft design in recent years, the author suspects this to be switching to higher engine bypass ratios may be what has changed contrails and our skies beyond previous recognition but yet also be what slowed global warming appreciably since approximately the start of this millennium.


However, we ought not to be complacent.  Increasing CO2 levels may not be causing global warming   but they are contributing to ocean acidity

http://www.pmel.noaa.gov/co2/story/Ocean+Acidification[12].  Furthermore we should not be complacent because although global temperature increase has stopped or halted, global climate change in the form of extreme weather events would appear at least in some parts of the world to be on the increase [13] http://focusonfloods.org/wp-content/uploads/2011/02/Observed-Variability-and-Trends-in-Extreme-Climate-Events-A-Brief-Review-Easterling-1999.pdf. Furthermore more contrails can affect planetary hydrology and the movement of larger weather systems.   Aircraft also inject aerosols into the atmosphere which absorb and scatter UVB [14]ftp://copernic.udg.es/pub/jordibad/98JD02350.pdf.  Given that 50% of Britain’s have been assessed as being Vitamin D deficient in the last 2 years there is another serious note of caution here. Contrails also reflect UV due to Rayleigh scattering. 



It would seem possibly that our saviour from run-away global warming is a chance event of inadvertent geo-engineering. Following logically from this it would seem that both aircraft and ships offer a cheap option for climate   and weather control in the future.

One possible problem is that some countries have already highly developed cloud seeding and microwave and ion based weather control systems, and, albeit these would only be expected to operate on a local basis weather is chaotic fractal system with often wildly  unpredictable knock –on effects.  

One can only hope that weather wars will not or have not already ensued. 


Further work

One can only properly test the aircraft global warming hypothesis fully by removing all aircraft from the skies. One can of course employ contrail avoidance strategies by flying at heights and places in the UT and below which are warmer or not at Relative Humidity conceive to contrail formation.  However even an aircraft without a noticeable contrail is still producing aerosol   and water vapour.  With regard to contrail avoidance there are also several patented methods for this used with certain types of military aircraft.  If it were practical to incorporate these into the civilian passenger fleet, contrail avoidance might be able to take place at heights and places in the atmosphere where less fuel would also be used. 



The present work strongly supports the hypothesis that it is global air traffic    and not anthropogenic carbon dioxide which has accounted for most global temperature changes in the period 1940 -2011.  A chance change in aircraft engine design has possibly been our saving grace from runaway warming.  The author concurs with Boucher that by adjusting the microphysics and or chemistry of contrails we should be able to take far more control over their global environmental effect in future.  In making such changes however, we should be very careful not to create scenarios which would starve our World’s population of essential UVB. [15]http://www.telegraph.co.uk/health/healthnews/9742176/Plethora-of-diseases-caused-by-low-vitamin-D.html or create global dimming to the detriment of vegetation on earth.

Of course finally no discussion of these topics would be complete without reference to either those who don’t accept any anthropogenic causes of global warming or those who think its demise is best left to mother nature, for example    [16] http://books.google.co.uk/books?hl=en&lr=&id=f5p76GoayfgC&oi=fnd&pg=PR5&dq=global+warming+hype&ots=l_TmZ1k76v&sig=fw_4HCTRyTo1u46hPUG88v5QyQE#v=onepage&q=global%20warming%20hype&f=false.




The author wishes to acknowledge his wife and son for interesting discussions on contrails.   He further wishes to acknowledge his son for providing interesting photographic evidence of weather research circular type of contrails. Finally the author wishes to thank Mr Peter Van Doorn of the Torro Tornado Research Organisation for years of valuable scientific contact and discussion.    



1.      http://www.dailymail.co.uk/sciencetech/article-2217286/Global-warming-stopped-16-years-ago-reveals-Met-Office-report-quietly-released--chart-prove-it.html.

2.      Olivier Boucher http://www.nature.com/nclimate/journal/v1/n1/abs/nclimate1078.html

3.      http://www.atm.damtp.cam.ac.uk/people/sf371/publications/fueglistaler06b.pdf

4.      http://www.met.reading.ac.uk/~sgs02rpa/PAPERS/Haywood09JGR.pdf

5.      Atlas et al 2006   http://journals.ametsoc.org/doi/abs/10.1175/JAM2325.1.

6.      http://directory.umm.ac.id/Data%20Elmu/jurnal/A/Atmospheric%20Research/Vol52.Issue1-2.Aug1999/835.pdf.  

7.      http://www-das.uwyo.edu/~geerts/cwx/notes/chap08/contrail.html.

8.      http://www.agu.org/pubs/crossref/1987/JD092iD04p04075.shtml.

9.      http://cat.inist.fr/?aModele=afficheN&cpsidt=2828565

10.  http://www.richmond.gov.uk/home/environment/pollution/noise_pollution/aircraft_noise/night_flights/current_limits_for_night_flights_at_heathrow-5.htm

11.  http://www.geoengineeringwatch.org/an-exaustive-list-of-patents/

12.  http://www.pmel.noaa.gov/co2/story/Ocean+Acidification

13.  http://focusonfloods.org/wp-content/uploads/2011/02/Observed-Variability-and-Trends-in-Extreme-Climate-Events-A-Brief-Review-Easterling-1999.pdf.

14.  ftp://copernic.udg.es/pub/jordibad/98JD02350.pdf. 

15.  http://www.telegraph.co.uk/health/healthnews/9742176/Plethora-of-diseases-caused-by-low-vitamin-D.html

16.  http://books.google.co.uk/books?hl=en&lr=&id=f5p76GoayfgC&oi=fnd&pg=PR5&dq=global+warming+hype&ots=l_TmZ1k76v&sig=fw_4HCTRyTo1u46hPUG88v5QyQE#v=onepage&q=global%20warming%20hype&f=false.