Even with those improvements, providing the energy to produce gasoline on a commercial scale  say, 750,000 gallons a day  would require a dedicated power plant, preferably a nuclear one, the scientists say.

According to their analysis, their concept, which would cost about $5 billion to build, could produce gasoline at an operating cost of $1.40 a gallon and would turn economically viable when the price at the pump hits $4.60 a gallon, taking into account construction costs and other expenses in getting the gas to the consumer. With some additional technological advances, the break-even price would drop to $3.40 a gallon, they said.

Image In a proposal by two scientists, vehicle emissions would no longer contribute to global warming. Credit... Alexander Ruesche/European Press Agency

A nuclear reactor is not required technologically. The same chemical processes could also be powered by solar panels, for instance, but the economics become far less favorable.

Dr. Martin and Dr. Kubic will present their Green Freedom concept on Wednesday at the Alternative Energy Now conference in Lake Buena Vista, Fla. They plan a simple demonstration within a year and a larger prototype within a couple of years after that.

A commercial nuclear-powered gasoline factory would have to jump some high hurdles before it could be built, and thousands of them would be needed to fully replace petroleum, but this part of the global warming problem has no easy solutions.

In the efforts to reduce humanity’s emissions of carbon dioxide, now nearing 30 billion metric tons a year, most of the attention so far has focused on large stationary sources, like power plants where, conceptually at least, one could imagine a shift from fuels that emit carbon dioxide  coal and natural gas  to those that do not  nuclear, solar and wind. Another strategy, known as carbon capture and storage, would continue the use of fossil fuels but trap the carbon dioxide and then pipe it underground where it would not affect the climate.