ASK an economist how best to reduce pollution, and the chances are that they will recommend taxing carbon emissions. And with good reason: doing so should encourage markets to find the least costly way to reduce pollution, something governments will struggle to discover themselves. In November Washington state’s voters will decide whether their state should mimic neighbouring British Columbia’s carbon tax, after a grass-roots campaign put the proposal on the ballot. It would be the first such policy in America. You might think environmentalists would unite behind such a pathbreaking effort. Instead, many oppose it.

Initiative 732, as it is known, would tax carbon emissions at a rate reaching $25-a-ton in 2018 and then rising by 3.5% plus inflation every year, to a maximum of $100 in 2016 dollars. Today’s levy in British Columbia is C$30 ($23) a ton. As in the Canadian province, the proceeds would be recycled into tax cuts elsewhere. The sales tax would fall from 6.5% to 5.5%. Low-income workers would get a tax rebate. And, to help placate affected businesses, manufacturing taxes would fall.

Yoram Bauman, who heads the Yes campaign (and who somehow makes his living by performing economics-themed stand-up comedy) proudly notes that three Republican state legislators support the initiative, and that it has not attracted the well-funded opposition from the oil lobby that a revenue-raising proposal might. Unfortunately, the price of that has been to alienate left-wing environmentalists, who are loth to give up the opportunity to use a carbon tax to fund new spending.

Their favoured projects include ideas to reduce emissions further, such as improving public transport. This is necessary, they say, because of the source of Washington’s pollution. Clean hydroelectric power accounts for almost three-quarters of the Evergreen state’s electricity production. As a result, transport is the biggest source of pollution. The estimated 25 cents that the initiative would add to the price of a gallon of petrol in 2018 seems unlikely to change driving habits. However, a recent study by Werner Antweiler and Sumeet Gulati at the University of British Columbia contradicts this argument, finding that the carbon tax there has encouraged people to buy more fuel-efficient cars, helping to reduce gas-guzzling by 7% per person.

Left-wing groups also insist that climate policy should include new spending on those worst affected by climate change. Near coastal Seattle, this means poor non-white neighbourhoods which are more vulnerable to flooding and, because they are nearer roads, have dirtier air, explains Ellicott Dandy of OneAmerica, a lobby group. As a reason to oppose the initiative, however, this too is unconvincing: any group that is disproportionately harmed by climate change should also benefit the most from the emission reductions.

More compelling is an urge to compensate or retrain workers in energy intensive industries who might lose their jobs as a result of the tax. But those who suffer because of market forces or technological change get little government help; it is oddly particular of environmentalists to hold up green policies on this basis, rather than arguing separately for, say, wage insurance.

The debate is ill-tempered. Mr Bauman did not get things off to a good start in 2015 when he complained about the left’s “unyielding desire to tie everything to bigger government” and “willingness to use race and class as political weapons in order to pursue that desire”. Members of one environmental group, the Sierra Club, performed parliamentary manoeuvres worthy of Ted Cruz: an attempt to change the group’s position from “do not support” to a more neutral stance was thwarted with help from Robert’s Rules of Order.

There are some problems with the initiative. It might encourage some businesses exposed to trade, such as aluminium manufacturers, simply to relocate to a different state. But environmentalists would be mad to pass up the opportunity the high turnout of a presidential election year presents to pass green initiatives—especially one as desirable as a carbon tax.