Natural gas-fired power plants only cause 2.3% of Ontario carbon emissions, but eliminating them would inflict at least a C$60 billion ($48 billion) bill on consumers, according to the Canadian province’s electricity suppliers.

The Ontario Energy Association (OEA), a utilities and contractors group, totaled the costs of environmental demands for swift and total greenhouse gas (GHG) emission cleanup in a report by Power Advisory LLC titled Implications of Shutting Down Ontario’s Gas-Fired Generators by 2030.

“A sudden retirement of all gas-fired generators will result in significant and material increases in electricity costs for all Ontario electricity customers,” the researchers said. “Alternative supply resources will be costly to construct and will, in many cases,...