A new exchange will allow natural gas traders to value the fuel based on methane emissions for the first time as the industry faces increasing pressure to help fight global warming. In the coming weeks, Xpansiv will launch an online trading platform that tags U.S. gas with data about its origin, CEO Joe Madden said. Certificates associated with that gas will be similar to renewable energy credits for electricity or the renewable identification numbers that are tagged to ethanol and other biofuels. “Until now you had no way to differentiate a molecule of gas,” Chief Operating Officer John Melby added. “You had no way to know how it was sourced or how it was produced.”