The United States Chamber of Commerce is facing a wave of defections over its opposition to legislation on climate change. On Monday, the national utility Exelon said it would quit the Chamber over its climate stance. The move follows recent departures by the utilities Pacific Gas & Electric and PNM Resources. The chamber has vocally opposed the Waxman-Markey climate bill approved by the House in June. It also recently called for a new “Scopes monkey trial” on the science of climate change. The call is a reference to the Scopes trial that pitted creationists against evolutionists in the 1920s. Exelon has supported the climate bill, but has a financial incentive to do so. As the nation’s largest operator of nuclear plants, it would benefit from raising fossil fuel costs.