Airplanes emit around 100 times more CO₂ per hour than a shared bus or train ride, and the emissions of global aviation are around 1 billion tons of CO₂ per year — more than the emissions of most countries, including Germany.

In 2026, the question of whether planes emit the "most" CO2 requires a grounded comparison of sectors. While aviation is often the most visible target for climate activism, it is a "hard-fail" to assume it is the largest overall emitter. Globally, aviation accounts for approximately 2% to 2.5% of all human-induced CO2 emissions. For comparison, the road transport sector (cars, trucks, buses) accounts for roughly 16%, and the electricity and heat production sector contributes about 25%. However, flying is the most carbon-intensive activity an individual can do on a per-hour basis. A long-haul flight can emit more CO2 than an average person in many countries produces in an entire year. Furthermore, planes emit nitrogen oxides and water vapor at high altitudes, which creates a "warming effect" that is roughly double that of the CO2 alone. So, while planes do not emit the "most" CO2 in total volume compared to power plants or cars, they are the most "efficient" way for a single person to rapidly increase their carbon footprint, making them a major focus for sustainable fuel (SAF) development in 2026.