I continue with the recovery of materials relating to research on the contrail (condensation trails) in past decades. And I 'have seen, among many supporters of the alleged evidence of "chemtrails", a strong increase in the use of the argument that before a certain date (1995) basically there were no contrails in the sky. Until you get to real challenges, retrieve old photos to show you they were contrails (not counting the obvious point, namely that in the past decades the traffic was much less than today).
As already ' I started doing this blog, the answer to this question is 'much more' simple. In fact in the scientific literature over the years there 'has been a growing attention to the phenomenon of condensation trails, mostly out of concern that with the increase in air traffic, the relative increase in contrail formation could lead to climatic changes ( leading to increased cloud cover, thus blocking a certain percentage of solar radiation). In many studies published even before the '90s, is a clear indication of condensation trails, how are visible and common, but how often is persistent over time.
Turning to practical examples, in a study of 1975 proposes the study of the contrail found in some satellite images of the island of Cyprus (full reference: Joseph JH, Levin Z, Y, Mekler, G Ohring, J. Otterman, "Study of contrails Observed from ERTS-1 satellite imagery", J. Geophys. Res, 1975, vol. 80, no. 3, 366-372 ). , The article reports - should be repeated - explicitly as the contrail formation of both normal and as the trails can be persistent enough to develop into cirrus clouds:
in Some Areas of heavy jet traffic, contrails released by a number of Aircraft May spread to cover a portion of the sky With thin cirrus-type clouds. The Possibility That May Such contrails lead to an increase in the average amount of high cloudiness and that such an increase of clouds may affect the earth's weather and climate has been raised [Murcray, 1970; Machta and Carpenter, 1971].
A parte questo, nel paper si ritrova una delle immagini satellitari usate:
Per la precisione, si noti che le immagini sono state prese nel 1972.
Un altro esempio e' uno studio del 1970 , sempre focalizzato su come le scie di condensazione possano influire sul clima (reference completa: PM Kuhn, "Airborne Observations of Contrail Effects on the Thermal Radiation Budget",Journal of the Atmospheric Sciences, 1970, vol. 27, 937-942 ). Anche in questo caso vale la pena di estrarre alcuni passaggi che rendono palese come le contrail fossero abbondantemente note, osservate e studiate:
The spreading out of jet contrails into extensive cirrus sheets is a familiar sight. Often, when persistent conditions exist from 25,000 to 40,000 ft, several long contrails increase in number and gradually merge into an almost solid interlaced sheet.
Nell'articolo si riportano dunque alcune fotografie di contrail, in territorio statunitense, come ad esempio:
La foto risale al 1969.
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