Hydrogen is not a transportation panacea–that’s the conclusion of a new calculation by two British researchers. In order for our fossil fuel vehicles to be replaced by true hydrogen automobiles, the U.S. would have to erect a million wind turbines or 1,000 extra nuclear plants. Anything else would continue to put greenhouse gases into the atmosphere and would not solve the problem of global warming.

Hydrogen is an energy carrier, not an energy source. In other words, it matters how it is produced. Most hydrogen today is made from methane, a process that releases carbon dioxide into the atmosphere. Or it can be made by splitting water molecules with electricity–but the electricity, today, is likely to have been generated by fossil fuels.

Hence the conundrum. Unless hydrogen is produced in a way free of greenhouse gases, the global warming problem remains. But generating it without introducing more greenhouse gases is, for all practical purposes, impossible. Remember that the next time some politician preaches hydrogen-powered cars as the cure of the future.