True sustainable tourism is about much more than reducing CO2 emission. The impact of a trip on the local community is just as important. Nevertheless the component that is easiest to measure is CO2. And that applies to much more than just touristic activities. Many of our daily activities produce direct or indirect emission. How much exactly can be quantified with the carbon footprint. This handy tool calculates your carbon footprint. (if you are using gas for heating, devide the cubic meters by 3 for the number of therms)