"The FCX Clarity’s only emission is water. Carbon Dioxide (CO2) emissions come only from the production of hydrogen, which varies by source; however, well-to-wheel CO2 emissions using hydrogen reformed from natural gas -- the most widely used method of production today -- are less than half that of a conventional gasoline vehicle. With the production of hydrogen from water by electrolysis, CO2 emissions can be further reduced and ultimately approach zero if the electricity used for electrolysis is generated using solar, wind, water, or nuclear power."