Ferretti, vice president at the Chicago Climate Exchange, extolled emissions trading, noting that the practice had helped bring sulfur dioxide and acid rain under control much less expensively than traditional command-and-control regulation.

FORBES: Carbon Emissions: The Next Sarbox

Back then, the concern was sulfur dioxide, the culprit behind acid rain.

FORBES: Is Obama Actually a Moderate Republican?

The limit is now set at about half of the amount of sulfur (the leading cause of acid rain) released in 1980.

FORBES: California's Carbon Caps are Contentious but Coming

Sulfur dioxide produces fine particulate matter and acid rain.

CNN: Nature - America's most wanted: Power plants urged to clean up their act

The sulfur dioxide and soot thrown off results not only in a polluted atmosphere but also acid rain that falls on a third of China's cities.

FORBES: Pollution And Prosperity

Media-fueled alarm about acid rain provided a basis for legislation to create markets for buying and selling excess sulfur dioxide (SO2) and nitrogen dioxide emission credits, and Project 88 became the Clean Air Act of 1990.

FORBES: Magazine Article