The Northeast’s cap-and-trade program generated $1.4 billion in net economic benefits over the past three years for nine states, even though electric power plants in the region took a $350 million hit to their revenues, according to a report released April 17.

Natural gas, oil, and coal plants experienced a revenue loss of $940 million over three years because they are required to purchase one carbon allowance per ton of carbon emissions under the Regional Greenhouse Gas Initiative requirements, the...