But here's the catch: If the total amount of air travel grows by more than 2.6 percent a year, then overall aviation emissions would rise.

Remember, the most optimistic scenario that Schäfer and his co-authors looked at envisioned the carbon intensity of aviation — that is, CO2 per passenger-mile — falling 2.6 percent per year between now and 2050.

The other question we've danced around so far is how much aviation emissions actually need to fall to avoid drastic climate change. This is a little trickier.

OK, this text is from Brad Plumer's report on CO2 emissions from world air travel.

Here at the outset I want to emphasize that I do not make this stuff up.

And right now, Schäfer notes, rapid growth in air travel seems quite plausible. As countries like China and India get richer and see their middle classes expand, more and more people are getting on airplanes and flying places. The expansion of travel alternatives like high-speed rail could help slow the growth in air travel demand, but it's unlikely to halt it altogether... [skipped some stuff, follow the link below] So how on earth can the aviation industry hit that 2020 target if technology alone isn't enough?

Yo, Brad! I can answer your question. And believe me, technology will not be enough in so far as it depends on a very large, continuous supply of low-carbon (cellulosic) biofuels which will not be forthcoming. (See the article).

And the answer is...

Humans are gonna have to stop flying! Stay home! Tend their gardens! Give it a try! People did it a hundred years ago. You can too!

But that wouldn't be Progress, would it? Homo sapiens would be going backwards, not forwards. So that sensible answer satisfies no one and will never be acceptable. Bogus alternatives must be found, and Brad found one.

I called Annie Petsonk, an aviation expert at the Environmental Defense Fund who is working with FlightPath 1.5°C. She argues that the airline industry will likely have to resort to carbon markets to make up that gap. The idea is that governments would come together and agree to a cap on global aviation emissions — say, they'd pledge to stay carbon-neutral after 2020. If airlines went beyond that cap, they would have to purchase carbon credits that essentially paid for reductions in CO2 emissions elsewhere in the world. Maybe that means buying renewable electricity for airports, or paying people to avoid cutting down forests.

Carbon credits? Bullshit!

There's a name for this kind of thing—it's called a shell game. Everybody is buying or selling carbon credits—this is market-based economics—but nobody is reducing emissions—this is simple physics. Doesn't work!

And so back to Brad's original question:

Growth in air travel could swamp technology improvements. So what then?

What then? Well, eventually, you can kiss your sorry ass goodbye.