Impact of air travel on CO2 levels

Looks like about 2-3% of human CO2 emissions come from airplane exhaust. That means that airplanes account for:

(3% from airplanes) * (0.7% increase in CO2 levels attributable to humans) = 0.02%

So, air travel accounts for 0.02% of the increase in CO2 levels. Lions and tigers and bears - oh my!

One of the news reports I read points out that "travel by ship produces 160x less CO2 than by air" which I had to laugh at. They don't give any explanation as to how they calculated that -- is that point-to-point or per hour, or what? I have a vision of super-commuters that were flying from NYC to L.A. now piling into ships bound for the panama canal aboard a giant, diesel powered beast, rumbling through the waters. LOL. Am I really to believe that a ship full of people crossing oceans over a period of weeks produces less waste than a jet in the air for 4 hours?