Is the hydrogen car going to fix globel warming?

The hydrogen combustion that you’re talking about is ultimately not the best use of the element in fueling automobiles. Fuel cells are far more efficient, and are emissions-free. The only hurdle to their mass production is, of course, cost. However, many laboratories across the world are looking for other materials than the platinum currently used as the membrane in proton exchange membrane (PEM) fuel cells. A break through in this area is approaching, although how far away it is is still a question.
Another potential problem for the propogation of hydrogen fuel-cell powered vehicles is a hydrogen infrastructure. Although the implamentation of such a thing would indeed be quite expensive (in the billions of dollars), similar amounts of money are spent annually in the defense budget and many other sectors of the U.S. Hydrogen embrittlement of steel is perhaps a larger issue in the way of this.
When it comes to hydrogen automobiles, they are, in truth, only as clean as the source of their hydrogen. Although they would be cleaner than current fossil fuel vehicles because of their efficiency and centralised Co2 production, if the hydrogen is produced from steam reformation via coal or electrolysis via any fossil fuel power plant than it is only partially green. Currently, the only method of energy production on a large scale, nuclear power, is seen by many as too problematic in terms of waste storage and safety. However, safety, in terms of potential meltdown and plant intrusion, is essentially a non-issue because of the containment buildings at all modern plants, as well as the high safety standards at any nuclear plant. Waste storage, as well, has a solution found under Yucca Mountain, despite what many anti-nuclear foundations would say about that issue….
Rambling aside, whether the hydrogen vehicle can be seen as a global warming-savior or not is dependant upon the method of hydrogen production more than anything else.