I came upon this a few weeks ago:
San Jose Mercury News:

In the first such program in California, and perhaps the United States, Bay Area air pollution regulators are proposing to charge an annual fee to thousands of businesses based on the amount of greenhouse gases they emit.
The fee – 4.2 cents per metric ton of carbon dioxide – would affect everything from oil refineries to power plants, and landfills, factories and small businesses like restaurants and bakeries.
“The climate is changing, and we think that everybody needs to help with the solution and pay their fair share to reduce greenhouse gases,” said Jack Broadbent, executive officer of the Bay Area Air Quality Management District in San Francisco.
“This is the next step in addressing the problem. The public is demanding that we be part of the solution.”

It’s a tiny amount compared to the [currently voluntary] trading price of carbon — and the potential infrastructure costs the Bay Area will face in dealing with the prospect of sea-level rise — but I think we can safely call this a milestone, and a harbinger of things to come.