SAN FRANCISCO — California’s fledging market-based system for reducing greenhouse gas emissions makes its formal debut on Wednesday with its auction of state-issued pollution allowances.

More than six years in the making, the state’s so-called cap-and-trade program sets limits on carbon dioxide emissions for virtually all sectors of California’s economy, the ninth-largest in the world. Emissions allowances are allotted to polluters, and companies whose emissions exceed their allocations must either obtain extra allowances or buy credits from projects that cut greenhouse gas emissions.

Almost all of the 23.1 million allowances that California has given out to utilities and industry for complying with the program in 2013 have been free; the auction will measure how they are actually valued by the market. Some 39.5 million allowances covering emissions in 2015 will also be on sale Wednesday.

Sealed bids can be submitted over the Internet in the three-hour auction, with the results to be announced on Monday.