“likely contrails are affecting precipitation to a much greater extent than are present deliberate seeding operations.” 
Illinois and New Jersey officials will not settle pollution suits against the nation’s major airlines out of court, despite Tuesday’s agreement between the airlines and the federal government to lean up the jet aircraft exhaust. Representatives of 31 major domestic airlines agreed to install “burner cans” to eliminate most of the smoke from their nearly 1,000 aircraft by 1972. 
The government will tell the nation’s 43 commercial airlines Tuesday that they must end pollution of the skies with jet engine smoke by 1972 or face punitive legislation from Congress. Mainly at issue is the installation of a redesigned combuster – or burner can – on 3,000 existing commercial jet engines of one maker that reportedly account for 70 percent of all smoke pollution from airliners. 
There will be a marked aesthetic improvement, since the so-called burner cans cut out something like 70 percent of the visible pollution and thus the familiar “black belch” will be seen no more. 
A jet air plane in one landing and takeoff drenches the environment with as much soot as 2,500 automobiles produce in a entire day … In addition to soot, jets also emit such injurious gases as carbon monoxide, aldehydes (irritants in smog), hydrocarbons, and nitrogen oxides ... jets using three major New York metropolitan airports emit 10,000 tons of particulate matter and carbon monoxide in a year. 
Despite airlines' promise to clear the sky of cirrus clouds by 1972, nothing changed.
The vapour trails, called contrails by the climatologists, don’t take long to spread out across the sky. They expand to a width of three kilometres in one hour, and to 32 kilometres in two hours. Observing one much-travelled air lane into Chicago that carries about 700 flights a day, Dr Changnon noted, "You can start off with a clear day in the morning and by evening Lhc sky will be covered by a cloud shield from jet contrails”.
Ho estimates some 2,000 commercial aircraft fly over Illinois every day. more than hair going to or from O’Hare.
“Illinois is definitely getting cooler, cloudier and rainier", he said. “While neighbouring States outside the flight paths are not". 
“Clouded Judgment: Do Jet Contrails Increase Cloud Cover?”
This video shows the mindset in pre-1980: contrail cirrus is a good thing!
“Unlike most changes in the atmosphere caused by man, this one is beneficial.” said Richard Semonin from the Illinois Institute of Natural Resources. “No one is trying to make clouds now using jet engines, but this study suggests that jet travel is inadvertently making our days more cloudy and some day, weather researchers may be able to use jets on purpose to change our weather.“
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