San Diego claims to be America's Finest City. And now it could become America's greenest city too -- a fine distinction.

San Diego wants to be clean -- 100 percent clean energy, to be exact -- in just 20 years, under an ambitious plan unanimously passed last week by the city council. This is big news. San Diego is America's eighth largest city, with a population of more than 1.5 million. It also has a Republican mayor, who, unlike his compatriots railing against climate action at presidential debates across the country, is making a bold plan that puts his city at the forefront of America's clean energy future.

The plan -- which got unanimous, bi-partisan support from the city council -- could become a model for other cities around the country to also move to 100 percent renewables.

Already, we've see that cities around the world are far ahead of national governments in taking actions toward sustainability. Whether it is banning plastic bags, setting up municipal composting systems, or shifting away from dirty coals, it is cities that paved the path for countries to make a climate accord in Paris just last week.

San Diego's plan is ambitious but realistic. It relies on expanding the city's vehicle fleet to 90 percent electric cars by 2035, expanding bicycles and public transit, creating more walkable neighborhoods, and better managing waste.

It helps that the city is already making strong, green moves. San Diego was ahead of the curve when it came to dealing with the state's drought, and has, thus, not had to see the same level of drastic cuts. Its local energy company is already at 33 percent renewables, ahead of the state's deadline and most of its peers in the supposedly more-progressive Bay Area and Los Angeles regions.

This will also be good for San Diego's economy. Mayor Kevin Faulconer sold this plan to businesses by hailing the financial benefits of going green. And if San Diego does become a green energy hub, expect its economy to expand as well, as study after study has shown that clean energy produces more well-paying jobs.

What would make this even better is if other cities decide not to let San Diego take the green mantle, but come up with their own, ambitious plans. In fact, that is exactly what many hope.

Evan Gillespie of the Sierra Club told the New York Times that San Diego has laid down a challenge to other cities. “We need others to see this and say, ‘Game on,’” he added. “We need places like Los Angeles, like San Francisco and New York, to step up.”

Exactly. We need more San Diegos. That's because, earlier this month, countries around the world agreed on an ambitious plan that would require us to completely stop using fossil fuels by 2050. San Diego's plan would put it nearly 15 years ahead of schedule – exactly the kind of strong ambition we need to avoid the 1.5-degree warming that scientists say should be the cap globally.

Image credit: Joe Wolf via Flickr