Live Science:  http://www.livescience.com/13462-contrails-climate-change-global-warming-clouds-air-travel.html

Science Daily:  https://www.sciencedaily.com/releases/2004/04/040428061056.htm

NOVA:  http://www.pbs.org/wgbh/nova/space/contrail-effect.html

Chemtrails Planet:  https://chemtrailsplanet.net/2015/03/27/chemtrails-nexrad-and-the-deliberate-engineering-of-climate-change-explained/

Bibliotecapleyades.net:  https://www.bibliotecapleyades.net/ciencia/ciencia_chemtrails34.htm

Metabunk.org:  https://www.metabunk.org/debunked-welsbach-patent-5003186-as-evidence-for-chemtrails.t6510/

Veterans Today:  http://www.veteranstoday.com/2013/12/14/correction-chemtrails-an-exotic-weapon-is-not-geoengineering-for-global-warming/