The Committee on Climate Change’s recommendation on aviation December 2020 (p10) has a pessimistic baseline scenario where no action would predict passenger demand growth of 64% by 2050. At the optimistic extreme it has a scenario of widespread engagement allowing for a drop of 15%, and works on a balanced pathway scenario predicting passenger demand growth of 25% by 2050.
Stay Grounded asserts that half of aviation emissions is caused by frequent flyers who represent just 1 % of the world’s population. Meanwhile, more than 80% of people have never been on an aeroplane.
The CCC’s growth of 25% by 2050 will happen as more people become prosperous and aviation continues with an easy tax regime.