While some states may be hesitant to sign on to those goals, the Sierra Club and the Acadia Center say the far higher emissions reductions would be worth the money.

Peter Shattuck, clean energy initiative director for Acadia Center, said while RGGI electricity prices could be $6 higher with the harder goals, emissions reductions would be three times bigger — looking like almost 20 million tons more of carbon per year.

“You can get much more of a reach at lower cost than I think folks would often assume,” Shattuck said.