SACRAMENTO, Calif. (AP) — California companies that must pay to emit greenhouse gases have saved up so many pollution credits it could hurt the program's ability to reduce emissions.

California runs one of the world's largest carbon markets, known as cap-and-trade. It requires companies to buy, trade or sell “allowances" equivalent to how much they plan to emit, and the state makes fewer available over time.

But the companies that participate have collectively saved hundreds of millions of credits and observers say that could undermine cap-and-trade's ability to spur emissions reductions.

The program is a key part of California's efforts to drastically lower emissions by 2030.

State officials who oversee the program say they have tools to deal with oversupply.