There was time in Los Angeles when the smog was so bad you couldn’t see down the block. Then, the state mandated that catalytic converters were installed in every car, which had to be submitted to regular smog checks. The new requirements were a boon for auto mechanics, who were authorized to carry out the emissions tests.

In that instance, California showed that regulations can be a blessing for business, while dramatically improving environmental quality — and it’s about to do it again. The state is debating a new climate policy that even Donald Trump could get behind.

The Buy Clean California Act would require the state to consider the carbon footprint of materials used in infrastructure projects when purchasing steel, glass, iron and brass. The measure, which has passed the state Assembly and is being considered by the Senate, would direct billions of dollars in spending to low-carbon suppliers. California would likely buy more steel from local steel mills and less from firms overseas.

Globally, steel production is huge source of carbon pollution. To make steel, manufacturers heat iron, limestone and a carbon-rich form of coal in a furnace. The process yields enormous sums of carbon pollution. Globally, steel accounts for 5 percent of greenhouse gas emissions, more than every plane on Earth.

Manufacturers can limit pollution by recycling scrap metal in an electric furnace instead of refining iron ore in a blast furnace, among other methods. California mills tend to be cleaner, by virtue of the state’s strict emissions limits — California has some of the most ambitious climate policies in the country.

“A steel mill in Rancho Cucamonga, California that produces rebar from recycled steel, complies with state and local emissions control requirements, and uses energy complying with the state’s renewable energy portfolio requirements, produces about half the greenhouse gas emissions as a mill producing identical rebar in Arizona,” said Kathryn Phillips, director of Sierra Club California.

Under the proposed law, the state would likely do more business with steel companies based in California and less with firms based in China. Direct emissions are only part of the equation. The state will also take into account emissions from transportation, meaning California will likely buy more locally sourced steel, cutting down on pollution from shipping beams, pipes and rebar long distances.

For this reason, the bill has earned the support of labor unions, including the United Steelworkers of America and the International Association of Bridge, Structural, Ornamental and Reinforcing Iron Workers Union. The bill would likely drum up demand for California steel, while discouraging U.S. companies from shipping operations — and job — overseas.

“Our members in California work in facilities that are complying with the toughest climate law in the country,” said Robert LaVenture, director of United Steelworkers District 12. The Buy Clean Act “will give companies and their workers preference if they are doing the right thing.”

California will spend around $10 billion a year on infrastructure over the next decade. That includes construction at public universities along with transportation infrastructure — roads, bridges and a multibillion dollar high-speed rail system that will stretch from Sacramento to San Diego. The state government is the largest purchaser of steel and concrete in California, and it can transform markets through the power of the purse.

Advocates championed the Buy Clean Act after discovering the state had purchased steel for the new Oakland Bay Bridge from a carbon-intensive Chinese mill, even though cleaner mills in Oregon and California had bid on the project. The measure will help level the playing field for local, low-carbon manufacturers.

Compare this approach to President Trump’s order that new oil and gas pipelines be made of U.S. steel. Rather than use environmental policy to direct purchasing decisions, he issued a memorandum calling on the Secretary of Commerce to “develop a plan.” By all accounts, a federal mandate to buy American-made steel would have only the flimsiest legal grounding, and would almost certainly fail to stand up in court.

“The State of California can’t reach out and set regulations in other states or countries,” Phillips said. But, it “can use its consumer power to motivate manufacturers to invest millions in pollution reduction to be competitive in a market worth billions.”

That has happened with the car industry. Following California’s regulation requiring catalytic converters, car companies began making the technology standardized. Since California buys 10 percent of all new cars in the United States, the industry tends to follow the state’s regulations. In addition, 13 states have officially adopted California’s car program, which now includes requirements for electric vehicles.

California’s steel bill does have one conspicuous omission — concrete. Like steel, concrete comes with a sizable carbon footprint. That’s because cement, the binding agent in concrete, is made by heating clay and limestone, with carbon dioxide as a byproduct. Producers can limit the carbon footprint of concrete by using alternative binding agents, such as fly ash, a byproduct of coal-fired power plants.

Some members of the industry are disappointed that concrete was not included in the latest draft of the bill.

“It would have provided the state with an opportunity to put their money where their mouth is,” said Jeff Davis, vice president of U.S. Concrete, a producer of low-carbon concrete. “I’m disappointed. I thought we had this thing headed in the right direction.”

Environmental protections can spur the development of new technologies and new jobs. Emissions limits have bolstered jobs in auto shops that carry out smog checks. Fuel standards have buttressed hundreds of thousands of jobs in facilities that produce parts for fuel-efficient cars and trucks. Now, the Buy Clean California Act is expected to support jobs in low-carbon steel mills. For this reason, the policy has earned the backing of both environmentalists and labor unions, two groups that historically have found themselves at odds.

“The policy needs to work for working people,” said JB Tengco, West Coast director of the BlueGreen Alliance, a coalition of labor unions and environmental groups. “The crazy thing is, it’s not that hard. Sometimes it requires compromise, but oftentimes it’s about searching for common ground.”

The Buy Clean Act has passed the state assembly and is currently wending its way through the state senate, which is expected to vote on the measure sometime this summer.

Jeremy Deaton writes for Nexus Media, a syndicated newswire covering climate, energy, policy, art and culture. You can follow him at @deaton_jeremy.