In terms of carbon emmissions way way worse. Like not even close. A cargo ship consumes about 91 times as much fuel as a plane per trip, while transporting about 6000 times as much cargo, meaning the plane burns about 66 times as much fuel per unit of cargo.
Jet fuel and marine bunker fuel both produce between 3.1 and 3.2 kg of CO2 per kg of fuel; jet fuel is slightly less dense at .74 kg/L vs .86 kg/L for marine bunker, but still planes are producing about 56 times as much CO2 per unit of cargo.
Marine bunker has way higher sulpher content, which is a whole other issue, but as of earlier this year not by as much. Until this year, sulphur for marine fuel was capped at 3.5% by weight, now it's down to 0.5%. Jet fuel, for comparison, is required to be under 0.3% by weight.
It should be noted though that planes release their emissions at higher altitudes, where both CO2 and sulphur do more damage, and ships can carry scrubbers to be cleaner (though many still don't) because they are not nearly as sensitive to weight as a plane. While in absolute terms there are larger sources of pollution, per unit of utility flying is one of the most polluting things humans do.
Considered and widely rejected due to issues like acid rain, ozone depletion, and decreased photosynthesis. Maybe if carefully distributed at optimal locations and altitudes you could maximize the cooling effects while minimizing damage, but random emission from flights in no way optimized for that purpose? No, it's just pollution.
Seconding what jjk said, also airliners cruise in the troposphere, not the stratosphere.
> From the planetary surface of the Earth, the average height of the troposphere is 18 km (11 mi; 59,000 ft) in the tropics; 17 km (11 mi; 56,000 ft) in the middle latitudes; and 6 km (3.7 mi; 20,000 ft) in the high latitudes of the polar regions in winter; thus the average height of the troposphere is 13 km (8.1 mi; 43,000 ft).
Airliners cruise around flight level 310-380 (31-38,000', about 5.9 to 7.2 miles).
Zeppelins have all the slow speed of ships and all the inefficiency of flight. Remember, planes spend very little energy on keeping themselves in the air (hence why unpowered gliders can stay aloft for hours), their engines are for overcoming drag, pushing large volumes of air out of the way. Airships move at much lower speeds, but they have immensely larger cross sectional areas. They don't need to push it as fast, but to travel the same distance they must push substantially more air out of the way. Airships are great if you need long endurance, for example for aerial photography, but they're a terrible option for transportation.
Jet fuel and marine bunker fuel both produce between 3.1 and 3.2 kg of CO2 per kg of fuel; jet fuel is slightly less dense at .74 kg/L vs .86 kg/L for marine bunker, but still planes are producing about 56 times as much CO2 per unit of cargo.
Marine bunker has way higher sulpher content, which is a whole other issue, but as of earlier this year not by as much. Until this year, sulphur for marine fuel was capped at 3.5% by weight, now it's down to 0.5%. Jet fuel, for comparison, is required to be under 0.3% by weight.
It should be noted though that planes release their emissions at higher altitudes, where both CO2 and sulphur do more damage, and ships can carry scrubbers to be cleaner (though many still don't) because they are not nearly as sensitive to weight as a plane. While in absolute terms there are larger sources of pollution, per unit of utility flying is one of the most polluting things humans do.