Under orders from a judge, California air quality regulators released a study Monday of potential greenhouse-gas-cutting measures, including alternatives to a controversial cap-and-trade system due to begin operations in the state next year.

But the analysis, from the California Air Resources Board, still gives cap and trade higher marks than any of the alternatives, including a carbon tax. As a result, the study is unlikely to settle the lingering debate over the state's cap-and-trade system, which will set a limit on greenhouse gas emissions and create a market for trading the right to produce those gases.

The air board has been developing a cap-and-trade system as a way to implement California's global warming law, which calls for cutting the state's emissions back to 1990 levels by 2020.

Looking at alternatives

But environmentalists sued the board, arguing that the regulators didn't fully analyze alternatives that might be more effective. In March, a Superior Court judge agreed, ordering the regulators to stop working on cap and trade until they performed a more thorough examination of the options.

Monday's study did not satisfy some of the environmentalists suing the board. The study examines the same alternatives to cap and trade that the board already considered and rejected. Caroline Farrell, executive director of the Center on Race, Poverty & the Environment, said her group wanted fresh options.

"The alternatives themselves weren't adequate, and so the whole thrust of the court's order, as well as our case, was that they should go look at some true alternatives to cap and trade," she said. "It wasn't just that they should go back and fill in some detail."

Public comment time

The air board is scheduled to reconsider its approval of cap and trade on Aug. 24, after giving the public time to make comments on the new report. But the study appears to favor the decision the board already made.

It finds, for example, that placing a tax on emissions of carbon dioxide, the most common greenhouse gas, would be politically unlikely because it would require a two-thirds vote of the California Legislature. A carbon "fee" could be created by a simple majority in the Legislature but would face restrictions on how the money could be used.

Setting hard limits on industry's greenhouse gas emissions through regulations, rather than a cap-and-trade system, would be difficult and could lead to increased greenhouse gas emissions outside the state, in a phenomenon known as "leakage." For example, owners of cement plants might choose to close their California plants and open new ones elsewhere, providing no real benefit to the environment.

E-mail David R. Baker at dbaker@sfchronicle.com.