<<Contrails could be eliminated if aircraft reduced their altitude from about 33,000 feet to between 24,000 feet and 31,000 feet...... if planes flew low enough to leave no contrails behind, their fuel consumption would increase by only four per cent>>
These people don't know what they are talking about. When climate scientists decide to look into areas not their expertise, then they come out with garbage like this. Had to fly back from MIA unexpectedly below 29,000' all the way instead of 33-39,000'. We used a darn sight more than 4% extra. To go even further down to 24,000'- we would not have made it- the differential would be large. Their figures are nonsense, so don't trust the rest of it! I shouldn't give it any further thought!