PaperTiger
I am sorry, but you, like many others, are drawing incorrect conclusions about this research because you have not read the actual source.
The authors of the paper (i.e. the scientists) DO NOT say that contrails do not form between 24,000 and 31,000 ft. Indeed, they say explicitly that they do. What they say is that the height of widescale contrail production varies hugely (and provide a mathematical function to describe this). As a result they are investigating the effects that would occur if cruising altitude were restricted when contrails can be formed at these altitudes.
In their calculations, the suggest the following:
June - September: altitudes up to 31,000 ft would be allowed, as contrail production at lower levels is limited (NOT zero though)
Nov-Jan: altitudes would be limited to 24,000 (or thereabout) as contrail production at higher levels is quite high
Other months: altitude varies between 24,000 and 31,000 ft
There is a graph in the paper to decsribe this
The 3.9% increase in CO2 production as a result of these altitude limitations seems to be quite in keeping with the very interesting figures provided by Notso Fantastic, given that this paper considers predominantly short-haul flights. Again I remind you that the authors explictly recognised that when long-haul flights were considered the figures would change:
'The results of this case study predict an annual fuel burn change only for the traffic mix and atmospheric conditions of the five states region in Europe. Other regions would be expected to
have a different seasonal cycle of maximum permitted cruise altitudes dependent on the local atmospheric conditions. The fraction of flights affected by those altitude restrictions would be
dependent on the nature of the traffic mix.'
Notso Fantastic, I can't work out what your comments about the hydrological cycle are meant to show. No-one is suggesting that once injected at high altitude the water stays there. Of course it is redistributed and rejoins the hydrological cycle. However, under current conditions the water is replaced by further air traffic, meaning that there is a nett long term impact.
This point was beautifully illustrated by the other research that we have been discussing, in which N. America became essentially contrail free during the short period of the Set 11th shutdown.
Oh, and by the way, I'm not that sort of Dr...but my wife is a physio if you need help for your back.
DrDave