That's absolute nonsense. Numbers vary, but domestic airliners have an industry average of about 51 miles per gallon of fuel per passenger. That puts it right around the average car trip (1.5 passengers).
Not saying air travel is bad but to play devil's advocate,
1. OP didn't give a reason for why we should slow down, but
2. if we presume environmental, then equating it to something else widely criticized for being wasteful and environmentally injurious isn't persuasive. At best, it is as bad, but we're well short of the best case, because
3. miles flown don't replace miles driven anywhere near one for one. The alternative to a cross-Atlantic flight isn't a cross-Atlantic drive. It's probably not even a cross-Atlantic cruise. More likely, it's a trip not taken at all, or as often. (Which is a bummer, of course!)
4. Both highways and air travel have conspired to chill investment in rail, which is the cleanest of the three.
5. Air travel is an economically-stimulating activity. I'd be very surprised if the net effect isn't more--probably many, many more--miles driven overall.
Of course there are lots of upsides to air travel and economic activity in general, but I feel like that's obvious!
