Methane (natural gas) is a greenhouse gas with a much more powerful warming effect than carbon dioxide, so finding and eliminating gas leaks is an important part of addressing the climate challenge. But until now, we’ve had poor information about gas leakage within cities, as well as how to correctly attribute the leakage all along the chain from well to consumer. In this episode we discuss a study, The Gas Index, with two of its authors. It is the first study that has provided granular estimates for life cycle methane leakage for a large number of cities, and the first to draw together recent assessments of leakage within cities, including leakage that occurs within buildings. It shows that cities’ gas systems are leaking about 72% more than had been previously estimated by the EPA. We also consider the role of natural gas in the energy transition, and some of the tradeoffs we will have to consider as we deal with the problem of methane leakage.