CarbonWise FAQs

We calculate the carbon dioxide equivalent (CO2e) emissions for each respondent for the survey period (7 days) using the latest Ministry for the Environment emission factors.  

Our methodology is aligned with the Greenhouse Gas Protocol (GHG) distance-based methodology for calculating employee commuting emissions.  

The calculation is:   

Distance travelled (km) x emission factor (gCO2e per passenger km) = CO2e emissions 

For example, imagine you commute a total of 100km in a week in a petrol car. The emission factor for a default private petrol car is 243 gCO2e per passenger kilometre.  

The calculation is:  

100 x 243 = 24300 gCO2e 

To get the annual emissions, we scale this value using an assumption about the number of weeks worked in a year, ordinarily 47.1 weeks.  

24300 x 47.1/1000 = 1144.53 kgCO2e 

CarbonWise uses the latest Ministry for the Environment emission factors.

The emission factor for a default electric car is 18.9 gCO2e per passenger kilometre. This is much lower than the emission factor for a default petrol car which is 243 gCO2e per passenger kilometre.  

Currently, CarbonWise uses the Ministry for the Environment “National Average for Bus” emission factor which is 155 gCO2e per passenger kilometre and the “Rail Average based on Wellington” emission factor which is 22 gCO2e per passenger kilometre.    

While the emission factor for electric bus is lower (15.4 gCO2e per passenger kilometre), only a portion of the fleet is electric in different locations and this can vary route by route. For simplicity, we are conservative and use the national average.  

If you use a company car, you can choose “car with someone” or “car by myself” as your primary mode. You will then have the option to select a vehicle fuel type. The selection options include petrol, diesel, hybrid, plug-in hybrid or electric company vehicle.  

Emissions from company vehicles are reported as business travel and are separate to commuting emissions. To accommodate this distinction, CarbonWise uses 0 gCO2e as the emission factor for company vehicles and so your estimated emissions will be zero per year.