The Triathlon World Championships eh?
Between January and October 2019 staff of the ITU took 1,471 flights covering 4,181,200 km and producing approximately 790 tonnes of CO2.
The Triathlon World Series events have roughly 120 athletes competing from all over the world, all of which will need to travel to Sunderland along with coaching and technical staff, family, friends and other associated hangers on.
I would suggest that the "environmental impact" of a small airshow mostly attended by locals will produce orders of magnitude less CO2 than an international sporting event.