Today I wanted to find out something about vapour trails and did what we all seem to do now and googled it ' BTW I dont like Google Chrome'All was good until I Looked at Wikipedia.Here is a chapter.
 September 11, 2001 climate impact study
The grounding of planes for three days in the United States after September 11, 2001 provided a rare opportunity for scientists to study the effects of contrails on climate forcing. Measurements showed that without contrails, the local diurnal temperature range (difference of day and night temperatures) was about 1 degree Celsius higher than immediately before; however, it has also been suggested that this was due to unusually clear weather during the period
The last sentence had me thinking ''well that's clever' duh