Warning: The Hydrogen Economy May Be More Distant Than It Appears - Popular Science: "Unlike internal combustion engines, hydrogen fuel cells do not emit carbon dioxide. But extracting hydrogen from natural gas, today’s primary source, does. And wresting hydrogen from water through electrolysis takes tremendous amounts of energy. If that energy comes from power plants burning fossil fuels, the end product may be clean hydrogen, but the process used to obtain it is still dirty.
Once hydrogen is extracted, it must be compressed and transported, presumably by machinery and vehicles that in the early stages of a hydrogen economy will be running on fossil fuels. The result: even more C02. In fact, driving a fuel cell car with hydrogen extracted from natural gas or water could produce a net increase of CO2 in the atmosphere."
