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Fuel-cell cars should be introduced gradually rather than adopted widely right away. Although they produce no harmful emissions from their tailpipes and can refuel quickly, making hydrogen often requires fossil fuels, which can create greenhouse-gas emissions. Supporters can counter that producing hydrogen with renewable energy would reduce this impact. Fuel-cell cars and refueling stations are also expensive, so an immediate large-scale rollout could burden consumers and taxpayers. However, careful investment and starting with areas where the technology is most useful could bring costs down over time. A gradual introduction would allow the technology and clean-hydrogen supply to improve before fuel-cell cars become widely available.