Washington state could be the first in the nation to enact a voter-approved carbon tax if a ballot initiative succeeds there in November, an outcome that supporters say would prove the political tenability of a major policy to combat climate change.

“Even being in a competitive position is a significant achievement,” Washington Gov. Jay Inslee, a Democrat and rumored 2020 presidential candidate, told the Washington Examiner in an interview. “If it doesn’t happen this year, we are not done."

However, if voters in this progressive western state reject a carbon tax for the second time, after voting down a similar plan two years ago, it may slow what modest momentum there is for pricing pollution at the national level.

“I do think about the consequences of it failing," said Noah Kaufman, a Columbia University economist who studies energy and climate change policy. “If a blue state fails again to pass a carbon tax, it certainly doesn't look good for efforts in states elsewhere, and at the federal level.”

The logic behind a carbon tax is simple, economists say: Raise the price of carbon intensive products — based on the damage they cause society — so consumers use less of them, and encourage producers to find other solutions to limit emissions.

But California is the only U.S. state to have a carbon pricing plan, imposing a cap-and-trade system that started in 2012, and anti-tax sentiment has led most Republicans to reject any form of the concept.

Supporters of this year’s version of the carbon pricing plan in Washington say they have found a winning formula. They strived to learn from the failures of the 2016 campaign, which had the rare distinction of repelling Republican voters (less than 20 percent of them supported it), and most environmental groups.

Yoram Bauman, an economist and stand-up comedian, organized the lightly funded 2016 effort, designing it to be revenue-neutral, meaning it cut other taxes by an equal amount of what would be raised. It achieved this by mostly cutting the sales tax.

But environmental groups, such as the Sierra Club, opposed that initiative, arguing the state government could achieve more meaningful emissions reductions if it used the revenue from the carbon tax to invest in renewable energy projects.

“Last time, it was an initiative without a home," Inslee said.

The 2018 version of the plan, supported by a broader coalition, would require fossil-fuel companies to pay $15 per ton of carbon dioxide they release into the atmosphere, beginning in 2020. That rate would rise $2 a year (plus inflation) until 2035, reaching around $55 per ton.

The carbon pricing plan will appear on the ballot as a fee, not a tax, to make the initiative more appealing to voters, and for technical reasons. According to Washington state law, money raised from a fee cannot be diverted to other unrelated purposes.

Money earned from the fee — roughly $1 billion annually by 2023 — would not be used to offset any other taxes. Instead, it would be spent on clean-energy and climate change resilience projects, such as wind and solar plants, mass transit, and energy-efficiency improvements to buildings. A lesser amount of the revenue would support rural and poor communities most vulnerable to climate change — and the higher cost of energy products that would result from the tax.

The changes have helped earn the measure the support of environmental, labor, tribal, and social justice groups.

But oil and gas companies oppose the new proposal, just like they did the first one, even if some are not so vocal about it — and are even backing a revenue-neutral carbon tax plan proposed by free-market groups at the federal level.

A political action committee formed by the Western States Petroleum Association, which represents companies such as BP, Chevron, Shell and Exxon, is spending millions to oppose the Washington state carbon fee, vastly outraising supporters. The opponents say the tax would raise the cost of gasoline and electricity without meaningfully lowering emissions.

"This is a costly, unfair and ineffective measure," said Dana Bieber, an official spokeswoman for the initiative's opponents.

Oil and gas companies don’t like certain aspects of the plan, and say it unfairly targets their products.

The proposal exempts roughly 20 industries from the carbon tax that are deemed to be crucial to trade for the state, and would have a hard time selling their products overseas if it is more expensive. The list of protected industries includes pulp and paper mills, glass, iron, aluminum, and cement, among others — but it does not include refineries.

Washington state’s only remaining coal plant is also exempted from the carbon fee, because its owners already agreed to shut it down by 2025.

“If you look at this from a business perspective for the oil and gas majors, it's not that surprising they oppose the plan,” Kaufman said. “There is very little upside for them. A carbon tax is always a tax on oil, coal, and gas. When you do that in a place with no coal, it’s a tax on oil and gas.”

But the impact of these omissions is minimal, Kaufman says, noting the trade-exempt industries produce 5 percent of the state’s emissions. Coal only makes up 2 percent of the state’s electricity mix.

That may be why some oil and gas companies, such as Shell and Exxon, say they aren’t actively lobbying against the Washington state carbon fee plan, even if a trade group they belong to is.

These companies, and many others, prefer a national carbon tax that would treat their products the same in each state.

Nick Abraham, an official spokesman for the initiative’s supporters, said it is aiming to overcome multimillions in spending from the industry-backed group by deploying more than 5,000 volunteers to knock on doors, make phone calls, and seek endorsements from local city councils.

Abraham, and others following the campaign, say polling for the initiative is tight, and can’t predict the result.

“I am not sleeping a whole lot of nights,” Abraham said. “We knew they would have to massively outspend us on the airwaves to compete with our field program.”

Kaufman said Washington state’s carbon fee, if it passes, may have a “modest” immediate impact, because Washington already has one of the cleanest electricity grids, running mostly on zero-carbon hydropower.

The biggest emissions reductions, he said, could come from spending on projects to electrify transportation, making it easier for drivers to shift away from gas-powered vehicles, to use more mass transit. Transportation recently passed the power sector as the higher greenhouse gas emitter nationally.

“People should have modest expectations for what the carbon fee will accomplish because transportation and industry are unlikely to change as rapidly as the power sector,” Kaufman said. “It would achieve emission reductions, maybe more so if the revenue is used efficiently. But it would not be something as dramatic as you'd see at the federal level where you would see a huge shift away from coal.”