I recall reading an article, but can't seem to find it, that studied changes in the atmosphere after the post-9/11 grounding of US flights. Granted, it was only free of condensation trails for a short period, but it was an unprecedented opportunity to test hypotheses related to their effect on the atmosphere.
The three or so days without US air traffic showed warmer days (because of lowered albedo, and thus less reflected sunlight) and cooler nights (because less of the earth's radiative heat energy was trapped). The thought, because of the efficiency differences of the albedo-vs-"heat blanket" effect that clouds bring, was that it was a net-warming effect that contrails cause. Scientists continued studied that, IIRC, and found that its contribution is indeed measurable, but accounts for an increase of something like 0.02° Fahrenheit.
The primary concern with commercial air traffic is their conversion of matter millions of years in the making to energy and waste products that have a more measurable effect on climate. The physical contribution of their condensation trails, via their reflective and absorptive properties, is a minor player. A player, certainly. I suspect air traffic won't decrease until we see other modes of transportation compete economically, which isn't happening any time soon.
The effect on daily temperature range is huge (1.1 to 1.8 degree C depending how you look at it). The effect on global average temperature is harder to get at, but it looks quite likely that planes increase average temperature. How much is very much in question and I'm skeptical of 0.02 degree F - that seems really low. Unfortunately we can't repeat the experiment and good models don't exist yet.
The three or so days without US air traffic showed warmer days (because of lowered albedo, and thus less reflected sunlight) and cooler nights (because less of the earth's radiative heat energy was trapped). The thought, because of the efficiency differences of the albedo-vs-"heat blanket" effect that clouds bring, was that it was a net-warming effect that contrails cause. Scientists continued studied that, IIRC, and found that its contribution is indeed measurable, but accounts for an increase of something like 0.02° Fahrenheit.
The primary concern with commercial air traffic is their conversion of matter millions of years in the making to energy and waste products that have a more measurable effect on climate. The physical contribution of their condensation trails, via their reflective and absorptive properties, is a minor player. A player, certainly. I suspect air traffic won't decrease until we see other modes of transportation compete economically, which isn't happening any time soon.