The new system will add costs "because it offers better cooling and an added fuel consumption lower than its competition," said Behr CEO Markus Flik in a speech last month in Stuttgart. "R744 is the refrigerant of the future," boasted Flik, using CO₂'s industry code name.

The CO₂ in air-conditioning systems is a fluid, compressed to as high as 140 bar -- five times higher than the maximum pressure in conventional car air conditioners. The liquid CO₂ absorbs and dispenses heat more efficiently than hydrofluorocarbon refrigerants, so the system can be engineered to deliver an equivalent amount of cooling faster and, on average, using less energy.

Of course operating at higher pressure requires tougher, more expensive parts. And it also requires a more sophisticated control system. In fact, Glober says that a CO₂-based system under conventional controls can exert substantial torque on the engine when it starts up -- enough to stall a small car.

Denis Clodic, director of the Center for Energy and Processes at École des Mines in Paris, points to another cost: establishing servicing networks for the high-pressure systems. "There is a lot of complexity to these systems. That means lots of training," he says.

Clodic predicts that, at least in 2011, CO₂–based systems will appear only in high-end luxury cars, and only in Europe. "We will see some thousands of cars made by Audi, BMW, and Mercedes, to show the European Commission that they really tried to prepare something alternative," he says. "But there won't be a mass market for 2011."

That is, assuming the hydrofluorocarbons from the chemical manufacturers pass muster in long-term testing. DuPont has said that it could take five years to commercialize its new hydrofluorocarbon refrigerant. By that time, companies like Behr may have overcome the remaining challenges with the CO₂ systems -- identifying affordable CO₂ sensors and reducing the cost of high-pressure hoses and compressors. If so, both technologies could enter the market -- initiating a classic competition based on performance and price.