With Palo Alto's housing shortage now a topic of national attention and residents increasingly calling for more housing options, City Council members agreed Monday night that two more-extreme scenarios for future growth should be evaluated as part of the city's process of creating an official vision that will guide it until 2030.

But the consensus belied plenty of divergent opinions, with some council members calling for the city to build thousands of new housing units and others favoring a more cautious approach that would protect its suburban ambiance.

As the council debated the ongoing update of the city's official land-use vision -- the Comprehensive Plan -- it took a series of close votes Monday aimed at shaping how this update will proceed.

The votes marked a hard-won milestone for a tortuous update process that began nearly a decade ago. In the end, the council embraced, with some modifications, the staff proposal to increase from four to six the number of growth scenarios that will be studied in the update's Environmental Impact Report (EIR). These include the four that had already been studied in the draft EIR and two new ones, which the council refined and agreed to pursue over a series of meetings last spring.

The two new scenarios go further than the original four in reducing the city's gaping imbalance of jobs to employed residents, which is currently estimated at about 3 to 1. (Read "Palo Alto struggles to provide housing that's affordable")

Both call for slowing down job growth, with each projecting 8,868 new jobs between 2015 and 2030 (by contrast, the business-as-usual scenario, known as Scenario 1, would generate about 15,480 jobs). But while Scenario 5 also calls for 3,546 new housing units by 2030, Scenario 6 calls for 6,000 -- far more than in any other alternative. The scenario would reduce the jobs-housing imbalance to 2.71 by 2030, still far higher than in most other jurisdiction, but lower than it is today.

What exactly would it take to achieve these more "sustainable" scenarios? According to a new report from planning staff, it would require a host of new zoning amendments, infrastructure investments and sustainability measures.

Like the four scenarios that have already been analyzed, the new scenarios would include zone changes that increase densities in transit-friendly areas, most notably downtown and California Avenue. Parking policies in these areas would also be revised, with paid parking becoming the new norm. Scenario 6 also calls for greater residential densities along El Camino Real, with sites near Stanford Research Park and Stanford Shopping Center eyed for housing opportunities.

Despite the 9-0 vote to move ahead with the new scenarios, council members sharply disagreed over the specific policies that would be analyzed. Councilman Tom DuBois proposed exploring a policy that would reduce the allowed density in certain commercial areas around California Avenue. In community-commercial (CC2) zones, the maximum floor-area ratio would be decreased from 2 to 1 1/2 in Scenario 5 (the ratio would remain 2 in Scenario 6).

The proposal moved ahead by a 5-4 vote, with slow-growth "residentialist" members and Mayor Pat Burt joining DuBois. Vice Mayor Greg Scharff, and council members Marc Berman, Cory Wolbach and Liz Kniss all dissented.

By the same vote, the council agreed to change a program that would have created "performance-based zoning," where developments would be approved based on their sustainability features and impacts on traffic, noise, aesthetics and other areas (the actual list has not been set).

DuBois and other council members affiliated with the residentialist philosophy -- Eric Filseth, Karen Holman and Greg Schmid -- voted against performance-based zoning and opted to retain the existing "density-based zoning." Burt joined them, giving them the bare majority.

While the discussion was long, wide-ranging and procedurally exhausting (the final motion was longer and included more than a dozen provisions), council members also recognized that they have plenty of common ground, particularly when it comes to their commitment to sustainable transportation policies.

Even so, some frustration was evident. Councilman Cory Wolbach, who in the past lobbied to study scenarios that are even more aggressive about building housing, again made his case. He lamented the fact that not a single scenario calls for as many housing units as jobs between 2015 and 2030.

Holman, who is considerably more cautious than Wolbach on growth, said she was troubled by the city's reliance on mitigations to take care of the problems that growth would bring. Mitigations, she said, can at times be "worse than -- and can't fully account for -- impacts."

"If everything we look at requires mitigations, I think we're going down the wrong path," Holman said. "We may be looking at too much happening here in terms of change."

Several residents shared their own concerns. Doria Summa, a College Terrance resident who serves on the Citizens Advisory Committee that is helping the city update the Comprehensive Plan, suggested that the city is "moving ahead with scenarios that do not represent the full range of options that the residents of Palo Alto want."

Summa, who was speaking for herself and not representing the committee, characterized most of the alternatives on the table as "high-growth options" and urged the council to consider scenarios more focused toward preserving residents' quality of life.

"I also feel like I'm looking at six baskets of groceries and I need something from each one and I can't combine them," Summa, who is affiliated with the citizens group Palo Altans for Sensible Zoning, said of the scenarios.

Some council members shared her concerns about what the process of mixing-and-matching the policies in the six scenarios will actually look like once the environmental analysis is complete and the time arrives to conclude the Comprehensive Plan update. Another critical question, posited by Burt, was: How will the city pay for the needed improvements?

It's important, Burt said, that "we don't just go throwing around ideal solutions without tackling the tougher issue of how to achieve them without necessarily achieving the funding."

"We have a lot of laudable goals but grossly inadequate revenue streams to achieve them," he said.

While this question isn't expected to get resolved any time soon, the council's unanimous vote at the end of the meeting represented a small but important victory for the update process.

First proposed in 2006, the Comprehensive Plan update stayed largely under the community radar until six years ago, when the Planning and Transportation Commission began revising each chapter. The council later decided to set the commission's work aside and launch a new process, which includes a 25-member citizens committee, a special planning summit, a long procession of public hearings and an environmental analysis with six alternatives.

Once the new scenarios are analyzed in a "supplement EIR," the document will undergo a public review process before the council adopts it. If things go as planned, the environmental document would be certified and the Comprehensive Plan adopted in the second half of 2017.

"I think we have to move forward at this point," Kniss said during Monday's discussion. "I think staff has done a great deal of work on it."

"I never guessed we'd end up with six scenarios," she added. "It's really a grocery cart full that we're choosing from."