Voters in Boulder, Colorado have approved what may the US’s first “carbon tax.” The tax, which will take to take effect in April next year, will be based on the number of kilowatt-hours used.

The tax is to pay for the “climate action plan,” efforts to “increase energy efficiency in homes and buildings, switch to renewable energy and reduce vehicle miles traveled,” the city’s environmental affairs manager, Jonathan Koehn, says.

The goal is to reduce the carbon levels to 7 percent less than those in 1990, which amounts to a 24 percent reduction from current levels. “The climate action plan serves as the roadmap to meet our reduction goal,” added Koehn.

City officials said the revenue from the tax will be $6.7 million by 2012, when the goal is to have reduced carbon emissions by 350,000 metric tons. Residents who used alternative sources of electricity like wind power would receive a discount on the tax based on the amount of the alternative power used.