Studies like these get based on the availability of fuel according to the IEA, which is paid for by Governments and whose job has always been to prevent 'panic' by 'reassuring' people that there is plenty of oil, and not to upset the Saudis' by calling into question their entirely unaudited claims of reserves, which remarkably have never changed by so much as a barrel after billions have been extracted.
If air travel is going to double or triple or whatever it will do on on something other than oil.

Actually Donough Shanahan it is hoped that by 2050 much of the land based traffic will be electrified, so even if it increases its GHG emissions should drop. However, unless we start building solar powered airships air travel will still need to burn hydrocarbons.

Both the military and commercial aviation industries have long recognized the need to find a renewable replacement for jet fuel. Different blends have already been flight tested and it's fairly evident that biofuels will be dominant within 20 years or so.

See today's GCC article:

UOP, PetroChina, Air China and Boeing to Collaborate with Government Agencies on Sustainable Aviation Biofuels Industry in China

It's too bad this article didn't take this into account, however, I believe that their projections of NOx will not be affected by renewable fuels.

It is known that automobile fuel use can be nearly eliminated by electric automobiles with an average non extended range of 20 miles. Range extenders should always be provided.

Fission reactors can produce and are producing hydrogen at relatively high cost right now, but this cost is less than the price of oil for the same amount of energy. And if the electricity is used in an electric car it may be more than five times as efficient and less expensive.

Thermal chemical processes can be developed and fitted to new and current fission reactors to produce even cheaper hydrogen. A process should be invented to produce CO from CO2 with heat or even first with electricity. This will allow the direct industrial recycling of CO2. Much of it can be done with existing processes.

Motorways can be electrified with methods invented a hundred years ago and also more modern methods at relatively low cost compared to the cost of the motor way, and the power to the contact is supplied with cheap direct current cables made with cheap sodium for the conductor. This electrification only suppliments the battery and fuel powered range extender with low cost, relative to gasoline, fission energy. There are very low losses with direct current cables and no power is being consumed.

Power can be beamed up from the earth to aircraft with radar waves very similar to the proposals to beam solar produced electricity down from space. (It would be cheaper to produce fission electricity in orbit and beam it down, and near earth space is already filled with radiation belts.) Power beam failure and take off is done with fuel in electric hybrid turbine and propellor systems. All planes with close destinations can be operated at lower speeds and higher efficiency without significant increase in total travel time considering time spent in airports and travel to and from airports.

Autotrains with the same Waggons used in the chunnel should be put in service between such cities, as LA and Las Vegas, to eliminate much of the need for and inconvenience with airtravel and extra overnight stays in hotels.

With very large battery bank locomotives now nearly economically possible with Durathon batteries, cheap non-continuous third rail electrification systems can be built, and all new light rail systems should eliminate the catenary and associated expense and distraction. Range extender engines now can garantee against electrification failure at low cost. Computer and electronic controls can eliminate cheaply most hazzards associated with third rail contact. Electronic high voltage direct current distribution cable systems are efficient and not as likely to be damaged.

The chunnel trains should be fitted with range extender engine generators that feed the motors directly without electronics for a speed of ten miles an hour. Microturbines can clean up the exhaust and supply lights.

There is a great deal of oil and even more coal and oil shale to make aircraft fuel, and every refinery should have several small nuclear reactors a hundred feet down for process heat. Using very high temperature steam from fission in gasification and refining processes can compensate more than fully for the fossil fuels used in aircraft. But then all coal now used for electric production can be diverted to liquid fuel production. ..HG..

Sanity Check: Something like 40,000 to 80,000 miles of high speed electrified trains could reduce short range flights to almost zero. China and EU are working at it and will meet that goal between 2020 and 2030.

That's another smart way to reduce liquid fuel consumption and GHG emissions. Electric trains are one of the lower cost and safest way to move people around.

Harvey.. do you have any idea how much high speed rail costs per mile?

Ill give you a hint .. just replacing a useful amount of air traffic with rail would cost more then building the entire h2 economy.

We could have made investments in rail, but went for the Interstate Highway system instead. It was seen that the private sector would take care of rail. That is why 2/3 of all freight is carried by truck today. Some decisions are SO important for the future that they should not be left up to idiots.

My point is that a lot of freight goes by big rigs that get 4 mpg with LOTS of roll and wind resistance when 2/3 should go by rail and not by truck. Long haul trucking may be cash flow for some, but may not be the best for the nation.