An article from the British magazine Nature reports on a study that may dampen the enthusiasm of some advocates of a hydrogen economy. The authors' research looked at the difficulties in generating hydrogen without producing large quantities of the very greenhouse gases that the use of hydrogen is intended to eliminate. Their calculations suggest mind-boggling numbers of windmills or new nuclear plants (a million or a thousand, respectively) would be needed to produce enough greenhouse-free hydrogen to run the US transportation system. There is sound logic here, but also a glaring blind spot.
Few of us really think about the scale of global fossil fuel use, and how it relates to sunlight. The world uses 3.4 billion gallons of oil every day, to put in more familiar units of measurement. Each gallon started as sunlight and plants, compressed and processed by heat and pressure underground. In the space of a couple of centuries, we will consume an energy larder that took millions of years to create. It stands to reason, based on this kind of concentration, that replacing fossil fuels would require harvesting today's sunlight (either directly with solar collectors, or indirectly by harnessing wind that is driven by sunlight) on a truly awesome scale.
So far, then, the authors' dose of reality holds up pretty well. But I believe they have fallen into the same trap as those who focus only on the pristine tailpipe emissions of a hydrogen vehicle, without considering the source of hydrogen. The only way to compare energy systems is to examine the effect on the entire system using a measure such as the "well-to-wheels" efficiency. This is where the hydrogen opportunity--even hydrogen created from fossil fuels--shines.
Because of the much greater thermodynamic efficiency of a fuel cell compared to an internal combustion engine (or any other heat engine), a hydrogen fuel cell based transportation fleet has the potential to cut greenhouse gas emissions by roughly half. Add to this the compounding effects of other efficiency improvements (carpooling incentives, better mass transit), and the potential reduction in greenhouse gas emissions is even more impressive.
So while we may not get to zero emissions this century, reducing current emissions by half or more would be a tremendous improvement. (The Kyoto Treaty targets a reduction of about 8% vs. a 1990 baseline.) Just to be clear, though, I'm not saying this will be cheap, easy, or quick. But putting up impossible targets and impractical pathways and saying that proves that hydrogen isn't worth the effort is obtuse and misleading.