In a very detailed article, Andrew Johnson recounts his attempt to correlate the frequency of air traffic over various parts of the UK with the frequency of persistent contrails observed in those locations.
http://www.checktheevidence.co.uk/c..._content&task=view&id=393&Itemid=50#_ftnref20
After much analysis, the conclusion of the report was what you would expect:
While there are various methodological objections that could be raised about this study, the primary problem is the ignoring of what 100 years of science tells us is the reason for persistent contrails: the weather.
Contrails persist in regions of air that are ice-supersaturated. Regions of ice-supersaturated air (sometimes referred to as Ice Super-Saturated Regions, or ISSR) are essentially invisible clouds. The plane passing through them makes them visible by temporarily raising the humidity. ISSRs vary in almost exactly the same way that clouds vary. So just like the sky can one day be clear, and the next day be cloudy, you can also have one day with no ISSRs, and the next day with lots, or a few broken ones (giving broken persistent contrails). And like clouds, ISSRs occur in layers, so planes flying at slightly different altitudes leave very different contrails.
None of this should be controversial. It's backed by science and observation dating as far back as the first observations of persistent contrails in the 1920s, and by discussions about contrails in over 70 years worth of weather books:
And this has been well discussed in the scientific literature for a similar length of time:
http://www.pa.op.dlr.de/issr/Cha1.html
So while I applaud Andrew's hard work, and the database created might even have some interesting data in it, it seems like he was looking at the wrong thing. Nobody had ever claimed that days with more contrails were the result of more air traffic. It's always been about the weather, at 28,000 to 40,000 feet.
http://www.checktheevidence.co.uk/c..._content&task=view&id=393&Itemid=50#_ftnref20
Contrails persist in regions of air that are ice-supersaturated. Regions of ice-supersaturated air (sometimes referred to as Ice Super-Saturated Regions, or ISSR) are essentially invisible clouds. The plane passing through them makes them visible by temporarily raising the humidity. ISSRs vary in almost exactly the same way that clouds vary. So just like the sky can one day be clear, and the next day be cloudy, you can also have one day with no ISSRs, and the next day with lots, or a few broken ones (giving broken persistent contrails). And like clouds, ISSRs occur in layers, so planes flying at slightly different altitudes leave very different contrails.
None of this should be controversial. It's backed by science and observation dating as far back as the first observations of persistent contrails in the 1920s, and by discussions about contrails in over 70 years worth of weather books:
And this has been well discussed in the scientific literature for a similar length of time:
http://www.pa.op.dlr.de/issr/Cha1.html
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