factoids from the california acad. of science

Well it's important to put that factoid in context too.  The main reason airplanes emit so much too is because they go so far.  If you drive your car across country, it produces a lot of emissions too!  Plus airplanes carry a lot more passengers than cars.  In terms of emissions per passenger-mile, airplanes are better over long distances than cars.

But of course the idea from this exhibit is that you should try to avoid travelling long distances as much as possible, period.

Indeed I do.  I outlined it in the Carbon Footprint Calculations wiki.

Essentially, for most cars (particularly hybrids) it's not difficult to find emissions statistics.  For example, for the Prius the CO2 emissions are 104 g/km.

According to the IPCC, long-haul flights emit about 32 grams of carbon per passenger-kilometer.  So if you've got 3 people in a Prius, it's just about the same emissions per passenger-km as an airplane flight.  If you've got 1-2 people, emissions per person are higher, if you've got 4, you've got lower emissions in the Prius.

However, it's also important to note that because airplanes emit their CO2 higher up in the atmosphere, it has a bigger effect on global warming than emissions from cars at the surface (by a factor of 2.7).  So effectively, the long airplane flight has the equivalent of 86 g/km per passenger, which means if you've just got 2 people in the Prius, you're better off driving.

Or even better yet, take the train!