The LA Department of Water and Power announced plans last week to be coal-free by 2025 after the utility confirmed it would sell off one coal-fired power plant in Arizona and grant approvals for a second plant in Utah to be converted to run on natural gas.

"This is a big deal," Gore said at the event at the LADWP headquarters.

"Only five cities in the world are leaders in this – London, Toronto, Copenhagen and Berlin and now Los Angeles. And Los Angeles is the only city in the United States to do this."

Sierra Coal executive director Michael Brune said the decision proved that coal’s days were numbered.

“Thanks to Mayor Antonio Villaraigosa’s leadership, the city of Los Angeles has proven that we as a nation can move beyond coal, cut dangerous carbon pollution and go all in on cost-effective clean energy,” Brune said.

“Across the country Americans are already seeing the benefits of replacing dirty coal with clean energy and energy efficiency.

“If a city like Los Angeles that was so deeply dependent on coal can move beyond coal, anyone can.”

The decision to sell and modify the two plants, which together provide LA with 40% of its energy requirements, is an emissions reduction unmatched by any major utility in the nation.

LADWP owns a 21% interest in the 2250 megawatt Navajo generating station, receiving 477MW of coal-fired power from the plant.

LADWP last week announced it would sell its stake in Navajo to Salt River Project, ending LA’s use of coal-fired power from the plant by December 31, 2015.

LADWP also holds a long-term power sales agreement with the Utah Intermountain power plant until 2027, contractually obliging it to purchase coal until this time.

In order to meet Villaraigosa’s target to quit coal by 2025, LADWP signed a new agreement with Intermountain and its other customers to convert the plant into a combined-cycle natural gas plant by 2025.

The conversion is scheduled to begin no later than January 1, 2020.

LADWP general manager Ronald O Nichols said the decision ended LA’s reliance on coal.

“We are very pleased that we have made progress with Salt River Project to enable moving forward with the negotiation of the final agreements that would enable LADWP to fully divest of coal power from Navajo by the end of 2015,” he said.

“Our effort to create a clear path to ending our use of coal-fired power from the Intermountain power plant is also a major achievement for a complex arrangement involving 30 Utah public power utilities and six California municipal utilities who receive power from that project.

“This allows us to focus on the new low-carbon future of Los Angeles.”

Villaraigosa initially set two goals – to achieve 20% renewable energy in the city’s mix by 2010 and to get LA coal-free by 2020.

The city has reached the 20% renewables goal.

Villaraigosa recently moved the target to quit coal back to 2025 because long-term sales agreements, such as the Intermountain contract, were proving difficult to modify.

"There were a lot of sceptics and naysayers out there when I talked about making Los Angeles the greenest, cleanest big city in the nation," Villaraigosa said at the Friday event.

"When I grew up, we used to have smog days where you couldn't go outside, couldn't have recess.

“When I became mayor, I knew we had to do something so my children and grandchildren wouldn't have to live that way."