Portland, Ore., has unveiled an innovative plan to slash greenhouse-gas emissions. The city will require an energy-efficiency inspection of new homes, then levy a tax on builders who have merely complied with Oregon’s efficiency requirements. Builders who construct homes 30 percent more efficient than the state building code requires will escape the fee; those who go above and beyond, with construction that saves at least 45 percent more energy, will be paid cash rewards. Portlanders will vote on the plan in January. Hint: vote yes!