It really depends on where the hydrogen is coming from. If it's being produced using electrolysis, and the electricity for that is coming from a coal-fired power plant, it's not much of a win, CO2-wise. However, if you can use Solar, Wind, Nuclear, Geothermal, etc., to produce the electricity, hydrogen fuel cells are a good deal, I think.

I believe in man-made climate effect but not man-made climate change - we are not tipping the balance, much less driving the climate in one direction or another. . Or we are. But there's little reason to believe we are. The science is...well, it's not science. Sorry. . Meanwhile on the real Earth that we actually live on and have lived on and will live on any 'green' technology that is based on a polluting technology is a shell game. Electric cars get electricity from coal pollution. Plastic bags were invented to save the trees but oh no! they turn out to pollute as do those plastic rings that hold six-packs together - in lieu of cardboard holders. . I don't mind improvements and less pollution. I kinda like the idea. . Unless it turns out to be as harmful or more harmful than what it was intended to replace in which case WHY spend extra money and government effort to break even?

It depends on the whole production cycle for the hydrogen -- just like for any other fuel. There is no fully non-polluting form of energy production. (Even solar panels and wind turbines require manufacturing facilities that involve melting glass and forging steel.) . I do tend to accept the argument that the carbon emissions we've been putting out for the last century or so are having an effect, as is the deforestation taking place to clear land for the production of, oh, ethanol. But I tend to think that it's more in the way of exaggerating a natural cycle. . In any event, the world is warming up (whatever's causing it) and research into alternative fuels and advanced technologies will pay dividends in dealing with whatever changes happen. I don't think it's necessary to embrace the "man as cause of global warming argument" to embrace the "sh** happens and the smarter you are the better you're able to deal with it" argument. . I do think it's important to take a good hard look at precisely what all these alternate technologies will mean. As others have noted here, it might be neat to know that my hydrogen fuel cell vehicle isn't emitting carbon. Nifty. But if the hydrogen plant is powered by a coal plant that's got to be added in. . I know that LA is worried about increased use of ethanol. Not that they're against it -- it reduces carbon emissions, but it can increase ozone emissions under certain conditions. It reduces emissions of some carcinogens, but boosts emissions of others. The net result appears to be a wash, but honest analysis requires recognition that there are positives and negatives to everything. . People forget that cars were (correctly) hailed as public health breakthroughs because their emissions were seen as healthier than those of their predecessor technology. (New York City used to have to collect several thousand tons of horse manure every day in the late 1800's. We have too many cases of asthma, cancer and heart disease, but when was the last time you ran across a case of cholera, typhus or diptheria?) . Anyway, I'll embrace hydrogen fuel cell cars if the power plants used to crack the water are nuclear. (That's not a joke.)