Renewing Boulder's carbon tax is essential if the city is to keep making progress toward reducing greenhouse gas emissions, but a potential county sustainability tax could make it harder to get voters to say yes in November, Boulder City Council members said Tuesday.

During a study session devoted to climate and energy issues, City Council members agreed that the Climate Action Plan tax -- set to expire in March -- should be placed on the November ballot as an extension of an existing tax.

But they expressed frustration that Boulder County appears likely to place a sustainability tax that would go in part to address climate and energy issues on the same ballot.

Councilwomen Lisa Morzel and Suzanne Jones said preliminary information from a Boulder County survey, which was shared with them by county officials, indicates support for both taxes is less than would be hoped for this far ahead of the election. Plus, they said, the survey shows support for the county tax was slightly higher than the city tax, and of those who would only vote for one, more chose the county tax.

Not renewing the CAP tax, which generates around $1.8 million a year for energy-efficiency and renewable-energy programs, would be devastating, city officials said.

"I'm very concerned that if the county goes ahead, our CAP tax will stand a very good chance of losing," Mayor Matt Appelbaum said. "And that will just kill us. That will set us way back. It would be a huge loss for us if we lost the momentum. There are many programs that are just getting going."

Councilwoman Suzy Ageton said the programs will "crash" if the tax is not renewed.

"We're going to go off a cliff if this doesn't pass," she said.

Concern about whether the carbon tax can compete successfully with a county sustainability tax comes as the city is adopting more ambitious carbon reduction goals and considering forming a municipal energy utility that would get more power from renewables.

The Climate Action Plan set the Kyoto Protocol -- reducing greenhouse gas emissions to 7 percent below 1990 levels -- as its goal. Even as the city, along with many other entities, has failed to meet that goal, climate scientists have warned that more urgent action is needed.

Boulder officials want to adopt climate neutrality or carbon neutrality -- net-zero man-made carbon emissions -- as the goal, which was supported by the City Council on Tuesday.

A recent report from Rocky Mountain Institute found that Boulder had achieved significant reductions in energy use at reasonably cost-effective rates, but that meeting the city's climate goals would not be possible as long as most of its electricity comes from coal-fired power plants. The difficulty of getting more energy from renewable sources from Xcel Energy is a major driver in the push for municipalization.

Several City Council members said they found the report difficult to understand and hoped its findings could be distilled in a way that shows voters what they've received for their tax dollars since 2006.

"There are two things we're trying to figure out," Jones said. "What can we tell people they got for their CAP tax and how will we get the most bang for our buck going forward, regardless of where the money comes from?"

Boulder Regional Sustainability Coordinator Jonathan Koehn said city staff is working on establishing 5-year climate plans, with targets or benchmarks for each year. Those climate plans would be integrated into all the city's master plans, from transportation and waste to grassland management.

At the same time, the community needs to be excited and engaged in the effort.

"This is not a suite of City of Boulder programs," Koehn said. "This is a community effort, and it depends on the entire community."

While Boulder can't make much of a dent in global warming by itself, its efforts can lead the way for other communities, council members said.

"What we can do ourselves is relatively small, but we can serve as a city on a hill and by our example have a much larger impact," Councilman Tim Plass said.

County officials are willing to work with Boulder on ballot language so that voters don't think the two taxes are redundant, Morzel and Jones said.

Morzel said the city needs to find a positive message, rather than appearing to put down the county effort, and explain to voters what the CAP tax has accomplished and could accomplish in the future.

"There is a lot more work that has to be done to hone the message we want to express," she said.