Always love the car analogies. They're really both interfaces, for petrol you get energy and CO2 emissions for a given quantity. However you don't know that th

Always love the car analogies. They're really both interfaces, for petrol you get energy and CO2 emissions for a given quantity. However you don't know that the CO2 emissions are net - the fuel might have been produced via some synthetic process driven by renewables. Unlikely, but as an interface you can't really know the details of the implementation behind the scenes.