But as tantalizing as they are, these goodies are peripheral to the challenge of delivering the quantum leap in efficiency that will satisfy environmental demands. In the long run, even shape-changing airplanes won't cut it.

"The real problem we face," says Ian Poll, "is not the airplane. It's the engine. The only feasible long-term solution is to switch the form of energy used."

This is where the ideas get bizarre. Hydrogen power would eliminate CO2 altogether, and it weighs only a third as much as regular fuel, but its adoption entails a gas tank as big as the plane itself. Daggett showed me such a concept, and the tank reminded me of an airship. ("I know," he said, "it's a Hindenburg of a tank. People still remember the Hindenburg!")

Poll's own favorite requires an even greater leap of faith: nuclear power. We have nuclear-powered submarines and aircraft carriers, and the switch to an airplane engine would not be technically impossible. The energy source, the reactor, would have to be shielded, and the shielding would be heavy, but a nuclear-powered aircraft wouldn't need gas tanks, could cruise over long distances without fouling the skies, and would not create a fuel fire if the airplane were to crash. Nonetheless, when Poll proposed it he could see my disbelief.

"Why not?" he asked. "For the last forty years, nuclear power has been demonized."

He said he frequently advances the idea at conferences. I asked him what reaction he got.

"People think I'm barking mad."

I come solidly back to earth in Seattle with Billy Glover, who, as managing director of Environmental Strategy, sits at the top of all of Boeing's efforts to work the magic. We talked about a lot of tweaking: refinements that will come in the generation of airplanes that follows the 787 Dreamliner (which itself has been an innovation breeder with an impact on the future); some much ballyhooed improvements in the efficiency of jet engines; and, something close to every traveler's regular torments, airport congestion and the subsequent mindless waste of energy as planes get locked in holding patterns or sit steaming on the ground.

"The hospitality industry, travelers, and particularly frequent fliers," says Glover, almost pleading, "would make a huge difference if they would consistently tell policymakers to get on with the air-traffic management issue. It's a matter of political will, not of technology. We could save up to eighteen percent of fuel costs right there."

But therein lies the rub. In the end, everything I saw and heard promised a series of incremental advances, not one transforming breakthrough. They will add up, of course. And they must happen. But, I wondered, was more possible?

"Is there a silver bullet?" I ask Glover, as we wind up.

"There's absolutely no silver bullet," he replies. "But there are a number of bronzes, and those are the ones we're looking for."

It is at this moment that Dave Daggett makes his noisome entrance. It might well turn out that there is silver (or even liquid gold?) in the jam jar–sized plastic bottle that he shows us in his presentation: harvested algae, murky and fecal before it transits to a smaller bottle of bio-crude and then, having been refined, emerges as clear and colorless as the beckoning mirage of an alpine lake.