Calculation of emissions from actual fuel use is more accurate than calculation from the distance driven. If you know your actual fuel use i.e. the number of litres used in a year, (for example from fuel card records) you can go straight to Step 3 otherwise start with Step 1.
Step 1: Identify your vehicle fuel economy
How much fuel does your vehicle use per 100 km travelled? If you're unsure of your car's fuel use you can either refer to the RightCar Database www.rightcar.govt.nz or calculate your own vehicle efficiency. This is easy:
1. Next time you fill up, record the odometer reading or reset the trip meter.
2. Drive the vehicle normally until the tank is nearly empty and refill the tank. Remember to fill to the first 'click' and don't spill any fuel.
3. Divide the number litres you filled (get this off the till receipt) by the distance traveled (from your odometer or trip meter) and multiply that by 100. depending on the vehicle size and driving style, you should have a number somewhere between 5.0 and 15.0
Step 2: How many kms do you travel per year?
Average travel estimates around 15,000km/year but this will vary depending on your own business travel needs.
Step 3: Work out how much carbon dioxide (CO2) your vehicle emits per year
This is calculated by multiplying together Step 1 x Step 2 x fuel type emissions level below.
CO2 Emissions for different fuel types (From the NZ Climate Change Office 2008)
Regular petrol - 2.32 kg CO2e/litre
Premium petrol - 2.37kg CO2e/litre
Petrol (default value) - 2.33 kg CO2e/litre
Diesel - 2.65 kg CO2e/litre
LPG - 1.61 kg CO2e/litre
Bio-Diesel (purely from NZ agricultural by product) - Zero net carbon emissions2
10% Ethanol Blend Petrol - 2.07kg kg CO2e/litre
Example: My car consumes 8 litres of petrol per 100km. I travel around 15,000km per year so my vehicle emits:
8/100 x 15,000 x 2.3 = 2,760 kg CO2 per year
Step 4: Work out how much carbon (C) your vehicle emits per year
Around 27.27% of CO2 is carbon. This step converts the kilograms of CO2 to tonnes of carbon emitted. This is done by:
1. Multiplying your kg CO2 from Step 3 by 0.2727 to calculate how many kilograms of carbon you produce, then.
2. Divide this number by 1,000 to convert it to tonnes of carbon
Example: 2760kg CO2 x 0.2727 = 752.6kg Carbon/year
o Divide by 1,000
o 752.6kg carbon / 1000 = 0.75 tonnes carbon / year (tC/yr). This is your total carbon emission.
Now that I've calculated my carbon emissions, how many trees do I need to plant?
Step 6: Work out how many trees need to be planted to offset your carbon.
Native trees remove from the atmosphere approximately 2.5 tC/ha/yr (on average), accumulating a maximum stock of around 500 tC/hectare for some forest types. Assuming around 2,500 trees per ha for a forest of indigenous species this equates to a sink of 1kg C (0.001 tC) per tree each year (the annual sink value). Over 200 years this accumulates to 0.2 tC per tree thus 5 trees are needed to offset 1 tonne of emissions (the cumulative total).
There are 2 methods to offset carbon by tree planting with native species. These methods reflect the fact that a small tree planted today will only sequester/ absorb significant amounts of carbon over a very long period of time.
Method 1 - Offset Now. This is a calculation where you will plant enough trees this year to offset your emissions from this year and emissions into the future. This option enables you to remove carbon from the atmosphere at the same time as it is being emitted from energy/fuel use. As a larger area is established the other environmental services provided by trees/forests are also enhanced, and a more emissions-intensive land use can be avoided.
Method 2 - Future Forest. This is a calculation where you plant as you go, planting enough trees each year to eventually remove carbon from the atmosphere equal to emissions from that year. However the benefits from the planting are significantly delayed as a smaller number of trees are planted over a longer period of time.
If you are happy that your emissions will eventually be offset by future sequestration, you will need to apply the cumulative total to determine the number of trees to be planted. Every tonne of carbon emitted is offset by planting 5 trees. The future sink capacity cannot be used to offset further emissions. So next year you will need to plant another 5 trees, and so on.
GreenFleet Future Forest Calculation
GreenFleet uses the Future Forest method. While recognizing the timing inconsistency of the Future Forest method, we like to encourage participants to engage in planting annually as a reminder of Greenhouse Gas impacts and provides an ongoing opportunity to engage with the local community and environment. It also allows the cost of offsetting to be spread over the length of time the owner operates it.
Example: 3.5 x 5 = 18 trees would offset this emission over 200 years. In our example, you would need to plant around 18 native trees to offset the carbon emitted by your vehicle in one year and would need to undertake annual plantings at this level.
Data from http://www.maf.govt.nz/forestry/pfsi/carbon-sequestration-rates.htm
7.0-9.2tCO2/ha/yr - General New Zealand mean net increment for Manuka/Kanuka scrubland during an active growth phase averaged over 40 years and taking into account changes in all carbon pools. 1.9 to 2.5 t C ha-1 yr-1
130 ? 600 tCO2 scrubland stock range
1000 ? 1200 tCO2 indigenous forests stocks
1 Different greenhouse gases (GHGs) have different global warming potentials. To enable meaningful comparison between gases GHG emissions are commonly expressed as CO2 equivalents (CO2e).
2 In principle, the burning of biofuels represents an approximately carbon neutral process. However, factoring in the energy required to plant, tend, harvest, process and transport the finished product can make the equation less favourable. There is currently a debate within the scientific community regarding just how much input energy is required to produce, process, and transport biofuels.