One problem I have in telling people that contrails can actually persist, and can even spread out to cover the sky, is that people tend to be suspicious of random people on the internet. So I decided to simply let 70 years of books on clouds speak for themselves.
Result: Every single book on clouds that I could find for the last 70 years says that contrails can persist for hours.
So next time some random guy on the internet tells you contrails can't persist and spread, then ask them why 70 years of books on clouds say the opposite.
My cloud book collection:
Selected References:
1991: National Audubon Society Field Guide to North American Weather
https://www.flickr.com/photos/metabunk/sets/72157644020551293/
1988: Exploring the Sky By Day, Page 49
https://www.flickr.com/photos/metabunk/sets/72157643850292503/
1981: Peterson Field Guide to the Atmosphere, page 137
http://www.flickr.com/photos/metabunk/sets/72157641675780313/
1972: Clouds of the World, page 130
https://www.flickr.com/photos/metabunk/sets/72157641669574294/
1969: Clouds and Weather. Page 28
https://www.flickr.com/photos/metabunk/sets/72157641629656855/
1957: Cloud Study: A pictorial Guide, page 79
https://www.metabunk.org/sk/1957CloudstudyapictorialguideOCR.pdf
1943 -Clouds, C. J. P. Cave, page 10
1943 - Cloud Reading For Pilots, page 73
http://www.flickr.com/photos/metabunk/sets/72157642316592915/
The above are simply the books I personally own. There are many other books that can be found in scanned form on the internet:
1983: Encyclopedia Britannica:
http://books.google.com/books?id=SBM8AAAAMAAJ&q=contrails "last for several hours"
1975 International Cloud Atlas:
http://library.wmo.int/pmb_ged/wmo_407_en-v1.pdf
1946, Brewer, Condensation Trails: Weather, June 1946
http://www.metoffice.gov.uk/media/pdf/c/3/1946_Brewer_condensation_trails.pdf
1921, July, U.S. Air Service
Result: Every single book on clouds that I could find for the last 70 years says that contrails can persist for hours.
So next time some random guy on the internet tells you contrails can't persist and spread, then ask them why 70 years of books on clouds say the opposite.
My cloud book collection:

Selected References:
1991: National Audubon Society Field Guide to North American Weather
https://www.flickr.com/photos/metabunk/sets/72157644020551293/

1988: Exploring the Sky By Day, Page 49
https://www.flickr.com/photos/metabunk/sets/72157643850292503/

1981: Peterson Field Guide to the Atmosphere, page 137
http://www.flickr.com/photos/metabunk/sets/72157641675780313/

1972: Clouds of the World, page 130
https://www.flickr.com/photos/metabunk/sets/72157641669574294/

1969: Clouds and Weather. Page 28
https://www.flickr.com/photos/metabunk/sets/72157641629656855/

1957: Cloud Study: A pictorial Guide, page 79
https://www.metabunk.org/sk/1957CloudstudyapictorialguideOCR.pdf

1943 -Clouds, C. J. P. Cave, page 10

1943 - Cloud Reading For Pilots, page 73
http://www.flickr.com/photos/metabunk/sets/72157642316592915/

The above are simply the books I personally own. There are many other books that can be found in scanned form on the internet:
1983: Encyclopedia Britannica:
http://books.google.com/books?id=SBM8AAAAMAAJ&q=contrails "last for several hours"

1975 International Cloud Atlas:
http://library.wmo.int/pmb_ged/wmo_407_en-v1.pdf

1946, Brewer, Condensation Trails: Weather, June 1946
http://www.metoffice.gov.uk/media/pdf/c/3/1946_Brewer_condensation_trails.pdf

1921, July, U.S. Air Service
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