Once you understand the scale of the operation, the environmental consequences become more apparent. As the Suzuki Foundation notes:
Jets account for somewhere between 4 and 9% of total human impact on the climate. .... A special characteristic of aircraft emissions is that most of them are produced at cruising altitudes high in the atmosphere. Scientific studies have shown that these high-altitude emissions have a more harmful climate impact because they trigger a series of chemical reactions and atmospheric effects that have a net warming effect. The IPCC, for example, has estimated that the climate impact of aircraft is two to four times greater than the effect of their carbon dioxide emissions alone.
Thus, comparisons such as the one below, which represent the comparative impact of carbon dioxide emissions alone and show air transport to have essentially the same impact per kilometer traveled as car transport, understate the impact of air travel.