Should it be CO2 g/kg?

The reason I chose CO2 is because it's already available in a convenient and comparable figure - g/kg has been used by Oatly and in the automotive industry. However, that's not to say it's the only option for this sort of regulatory measure - an alternative would be a regulatory score assigned to companies based on a number of environmental factors, CO2, recyclability, refillable, process waste etc. As long as it results in a single comparable score across the industry, and is a legal obligation.