This time around, there are notable differences. The earlier efforts called for carbon taxes; this year’s version is technically not a tax but a fee, which may sound more palatable to voters. Unlike tax receipts, which legislators could get their hands on to use for other purposes, the fee revenue would have be spent on efforts like carbon and pollution reduction and forest health programs under a specified formula.

Some environmental groups opposed the previous ballot measure because it also would have lowered other taxes, meaning that the state would not have netted much new revenue for climate or energy projects.

Huge money is flowing into the campaign, making it one of the most expensive ballot-measure campaigns in state history. More than $26 million has been raised to oppose the fees, mostly from the oil and gas industry, while more than $14 million has been raised in support. Michael Bloomberg, the former mayor of New York City, contributed $1 million to back the initiative, as did Bill Gates, the billionaire philanthropist. Microsoft, the company Mr. Gates co-founded and a huge economic force in the state, came out in support of the initiative last week.

If the carbon fee initiative passes, the investments it would finance could include anything from energy efficiency upgrades to electrified transit projects. Aid to low-income residents and to workers who are displaced from fossil-fuel industries are built into the measure as well.

Washington starts the conversation about energy at a different place than any other state in the nation. By virtue of the region’s topography, hydrology and the engineering feats of the federal dam builders who began remaking the Columbia River basin in the 1930s, the energy debate in the Pacific Northwest is distinct.

Large-scale power production from the dams — more than twice as much as Oregon, the No. 2 state for hydropower output — means that Washington already emits less carbon dioxide for each unit of energy it produces than any other state, according to federal figures. What’s more, the Pacific Northwest has little oil or gas to drill for or fight over, and the region’s coal deposits have played out or become uneconomical.

Supporters of a carbon fee say the state’s extensive base of renewable, nonpolluting energy makes it the perfect laboratory to test efforts like this, because the economic impact would be less dramatic than in big coal states like West Virginia or Kentucky.