In the 1960s, a University of Wisconsin graduate student named Thomas Crocker came up with a novel solution for environmental problems: cap emissions of pollutants and then let firms trade permits that allow them to pollute within those limits.

Now legislation using cap-and-trade to limit greenhouse gases is working its way through Congress and could become the law of the land. But Mr. Crocker and other pioneers of the concept are doubtful about its chances of success. They aren't abandoning efforts to curb emissions. But...