THE FEEL-GOOD stage of California's leadership on global warming is unsustainable. Kudos to the pop stars with their calls to switch lightbulbs and unplug cellphone chargers when not in use. But we can't pretend that we will actually reduce 2020 greenhouse gas emissions to 1990 levels without tackling our region's embedded patterns of auto dependence and suburban sprawl.

"A subway to the sea" remains largely talk. Instead, nearly $1 billion is being allocated to widen a stretch of the 405 Freeway. L.A. County transit fares have been hiked again, while Caltrans and the Metropolitan Transportation Authority continue to pursue the boondoggle of tunneling under South Pasadena to extend the 710 Freeway. In local City Council deliberations and planning commission hearings, business goes on as usual, with developers trying to jam as much density as possible into their projects and neighbors fighting them every step of the way.

Halting the slide toward irreversible global climate change starts with envisioning a new and better way of life. That is not as utopian as it sounds. Americans have risen to great urban challenges before.

At the close of the 19th century, the United States led the industrial world in rapid growth and change. Our cities were both the pride and shame of the nation. In 1893, Chicago launched the "City Beautiful" movement with the Columbian Exposition. The magnificent dream city that was erected on the shores of Lake Michigan was not only the launch for Ferris wheels and chewing gum, it was the inspiration for a national movement to lift the nation's cities above their harsh and chaotic conditions by creating great parks, civic centers and grand boulevards.

Frederick Law Olmstead Jr.'s design for Torrance, along with landmarks such as the Pasadena Civic Center, Griffith Park, San Clemente's downtown, Ventura's City Hall and the canals of our Venice, are the local legacy of that great crusade to civilize our booming cities.

A different kind of challenge faced the United States half a century later. Ten years of the Depression had devastated our cities. Americans were weary of living in tenements next to gritty factories. Sparked by the imagination of "radiant city" pioneers like Frank Lloyd Wright, the 1939 New York World's Fair launched the nation's most sweeping reshaping: suburbia.

General Motors showcased this vision in its "Futurama" pavilion. Millions of Americans waited an average of four hours to see a fantasy land of tract homes, shopping centers and business parks connected by free-flowing ribbons of highways. As they exited, they got a glimpse of the sleek GM cars designed to speed them toward this idealized landscape and a button that read, "I have seen the future."

Los Angeles emerged as the quintessential embodiment of that vision, the landscape of the future that spun off emulators around the globe. The "California dream" remains a suburban one, enforced by rigid zoning codes and churned out by developers on autopilot.

A countermovement to re-glamorize urban life has tentatively raised its profile in recent years. Residential towers rise south of downtown Los Angeles, lofts are sold to young professionals in Santa Ana and condos are built next to transit stations in Hollywood and Long Beach. But these exotic implants remain isolated islands in a sea of auto domination. Little wonder that residents there have failed to embrace car-free lifestyles when transit remains so limited and unattractive to anyone who has other choices.

It will take a far more sweeping urban renaissance to slash greenhouse gas emissions and our costly thirst for imported oil. It may be too late to wean aging baby boomers from their devotion to a suburban lifestyle that's unsustainable beyond their lifetimes.

That leaves the younger generations of Southern Californians with the challenge of inventing a landscape that can produce both livability and prosperity to support a 2020 population at 1990 emission levels.

It will take more than alternative fuels to bring about this nirvana. It will require finding room inside our already developed footprint for significantly more people and serving that larger population with real alternatives to auto mobility. Caving in to developer demands for more density will backfire without far greener urban building, far better urban schools, far more attractive urban parks, far safer urban streets and far more equitable ways to fund vital urban services.

It's easy to be pessimistic about the prospects for such a model to emerge here. L.A.'s charismatic mayor has lacked the focus to lead such a far-reaching transition. Local media seem more enamored of following Paris Hilton than of learning from Paris, France. The bureaucrats who run metro planning and transportation agencies talk a good game but take no risks. Real estate barons claim their mega-projects will save our cities, except their designs don't actually connect to them.

Yet there are also grounds for hope. Some planners, architects and developers are creating little gems that serve as promising models for what could be the new standard. The emerging downtowns of Pasadena, Santa Monica, San Fernando, Ventura and Glendale are catching the attention of more and more residents as alternatives to living in the suburbs or driving to the mall. But like switching lightbulbs, these hopeful prospects will remain noble gestures without a unifying vision and movement to propel them into the mainstream.

Meanwhile, the planet is getting hotter. The real work is ahead. But as President Kennedy told us baby boomers when we were youngsters, meeting a global challenge is important and ennobling: "I do not shrink from this responsibility — I welcome it…. The energy, the faith, the devotion which we bring to this endeavor will light our country and all who serve it — and the glow from that fire can truly light the world."