Hill: A once-obscure metric of carbon emissions toll is becoming the talk of K Street or at least a corner of it. Two oil companies and big coal producer have begun lobbying on the social cost of carbon, signaling increased interest and concern over how regulators calculate the benefits of avoided pollution. Second-quarter lobbying filings show that coal giant Peabody Energy, oil-and-gas producer Marathon Oil Corp. and refiner Tesoro Corp. all list the topic among their lobbying issues. Their filings...