Is hydrogen better for the climate?

A couple of years ago I wrote a series of articles about hydrogen. There was a lot of attention on it at the time, and several pilot studies were underway. Two years later a degree of clarity is emerging around the role that hydrogen might play in reducing emissions, but it depends on three important questions:

Does it work?Is it affordable?Is it green?

The answer to the first question is a qualified yes. There are hydrogen powered buses on the streets. There are trains, cars, sh...