"A new era of clean power is dawning and we're blazing a new trail for the rest of the country and the world to follow," he said.
At the event downtown, the mayor was joined by former Vice President Al Gore.
"I want to say in the strongest way I possibly can, this is a really big deal," he said.
Right now electricity from the Navajo Generating Station in Arizona and the Intermountain Power Project in Utah make up 39 percent of the energy purchased by the DWP. Under the plan, the city will sell its share in the Navajo plant and convert the plant in Utah to natural gas.
Gore said only a handful of cities in the world have done anything like this.
"Los Angeles joins that list of the five greatest cities in the world where combating global warming is concern," he said.
But not everyone at DWP is sold on the plan.
"The problem that I have is that nobody has told us what this is going to cost," said Jack Humphreville, president of the DWP advocacy committee. "In the past, DWP numbers indicated that the early phase out of Navajo was going to cost us $800 million, and the early phase out of the Utah facility was going to cost us $1 billion."
Humphreville says the higher cost to buy electricity from other sources will be passed along to rate payers.
"Over the next five years, our rates are supposed to increase 36 percent according to DWP projections, and according to other documents from DWP they're going to double over the next 10 years," he said.
DWP General Manager Ron Nichols said the rate increase is nothing to worry about.
"Despite the fact that we will have higher rates, and we will, and we've been very clear about that, those rates are still going to be among the lowest rates in California," said DWP General Manager Ron Nichols.
The city still has to negotiate a contract to sell its share of the Navajo plant, and it then has to be approved by the City Council.