The issues with aviation are two-fold: First, the amounts of emissions are very high relative to total passenger throughput. Second, the issue is very difficult to address meaningfully, because heavier-than-air aircraft have inherently high energy requirements that must be fulfilled by very dense, high-quality fuel, which we have no way to sustainably produce in sufficient quantities.

This video series explains the issues well: https://www.youtube.com/watch?v=k50qD40p3WU&list=PL_AaC0duf8...