The change will mark a major shift to renewable and other cleaner forms of energy for America’s second largest city within 12 years.

On Tuesday, commissioners at the Los Angeles Department of Water and Power (DWP) moved forward with plans to dump the utility’s interest in a coal-burning plant in Arizona and convert another one in Utah to natural gas. The plants provide nearly 40 percent of the city’s energy to a population of 3.8 million

Those changes, coupled with new commitments to renewable power, would make the city coal-free in 12 years – something broadly welcomed by environmentalists.

“Los Angeles is setting an extraordinary example to other fossil fuel dependent US cities that they too can end their dependence on coal and switch to renewables,” said Bellona President Frederic Hauge. “If America’s second largest city can do it, so can the rest.”

Hauge and Bellona Advisor Svend Søyland, however, acknowledged that Losa Angeles’s plans would have eventually materialzied as a result of market forces anyway.

“Before we pop the champagne for Los Angeles’s Mayor, let’s remember that this is a trend primarily driven by market forces and the ‘dash for gas,” said Søyland. “There will be a benefit from shifting to gas. If the methane leaks at the gas wells in the shale gas operation exceeds 3.2 percent the entire benefit [to net emissions reductions] dissapears.”

The switch off of coal comes two years earlier than a state-imposed deadline that requires the utility to be coal-free by 2027, when its contract with Utah’s Intermountain Power Project runs out.

But it is five years later than a target set by Mayor Villaraigosa at the outset of his second and final term, when he pledged to drop coal completely by 2020. Shakeups in DWP leadership, the failure of several renewable energy proposals and the grip of long-term contracts with out-of-state power producers have kept the mayor’s goal out of reach, the Los Angeles Times reported.

Still, Villaraigosa is expected to burnish his environmental credentials with the move.

He declared victory Tuesday, calling the coal divestment plan “game-changing” even though it won’t meet the timeline he set.

“I believe the only way to get the goal is to set aggressive timetables,” he told the newspaper. “Climbing mountains that have never been climbed before [isn’t] easy.”

Villaraigosa’s office issued a news release with a congratulatory quote from former President Bill Clinton and announced the plans for a Friday news conference celebrating the measures with environmentalists and Gore whose efforts to make climate change won him a shared Nobel Prize with the United Nations Climate Panel in 2007.

The city’s DWP is in negotiations to sell its 21 percent share of the Navajo Generating Station in Page, Ariz., which will allow the utility to stop receiving power from the plant by 2015, four years before its current contract is up.

Getting free of coal at the Intermountain Power Project in Delta, Utah, is more complicated because the DWP does not own the plant and is bound by contract to buy its power through 2027.

On Tuesday the Board of Water and Power Commissioners approved an amendment to its contract with Intermountain Power to allow the plant to transform its power supply to cleaner natural gas, the Los Angeles Times said. The gas plant would be smaller than the current one, freeing up space along existing transmission lines for new renewable energy projects.

The plan still requires the agreement of the Los Angeles City Council.

Cost questions linger

But questions remained about how much the plan would cost. The utility’s commissioners did not discuss how the changes would affect electricity rates for customers.

A report released by the utility last year estimated that ending coal-power consumption at the Utah plant four years ahead of schedule would cost nearly $1 billion over four years in higher replacement fuel costs and other expenditures.

DWP General Manager Ron Nichols told the Los Angeles Times that the exact costs will be determined over time.

But he said that getting out of contracts that require the city to buy coal is a smart move, given new federal regulations that will require many coal plants to make costly improvements to reduce emissions in the future.

“It’s the least risky approach forward for us,” he said.

The DWP’s ratepayer advocate said he supported the acceleration of the phase-out of coal, but that he wants to see more details about how the city will provide reliable power, and at what cost.