California's revamped low-carbon fuel standard took effect early July, despite fierce Republican criticism and increasing Democratic trepidation over its potential to raise gas prices.

The new rules, which expand a program to reduce climate- warming gases and clean the air, ratchet up requirements for cleaner fuels and broaden a $2 billion credit market aimed at cutting emissions from cars, trucks, and freight.

Governor Gavin Newsom's office issued a fact-check memo defending the rule and saying the impacts are exaggerated, while Republicans in the legislature and Congress say it would damage the economy because Californians already pay the most of the nation for gasoline.

Democratic lawmakers introduced legislation that would cap the price of the standard's fuel credits in an effort to rein in price spikes at the pump.

The measure is supported by one of the state's most powerful Democrats, Senate President Pro Tem Mike McGuire, who said it will reduce costs for drivers across the Golden State while continuing to move our climate and energy goals full steam ahead.

The new fuel standard is projected to reduce carbon dioxide-equivalent gases by 558 million metric tons through 2046, according to the Air Board's economic assessment.

Those reductions are equal to the emissions of more than 120 million cars on average in a year.

Cleaner, low-carbon fuels include biofuels made from soybeans or cow manure.

The program has been particularly successful in reducing the diesel fuels used by medium and heavy-duty trucks.

Over the 13 years, it has displaced 25 billion gallons of petroleum fuels, according to the Air Board.

Experts say the future impact is uncertain because it depends on how much the oil industry spends on buying credits and then passing it on to consumers.

For CalMatters, I'm Alejandro Lazo.