The Numbers
Whilst the overall concept of carbon offsetting to prevent climate change is widely agreed, the details of how requirements should be best calculated are still widely debated. Here we provide some simple examples of how we do about calculating the carbon offset requirements for our partners.
Air travel
We provide carbon offsets for air travel as part of an organisational assessment, by providing travel companies with offsetting packages for their guests and to individuals who wish to offset this element of their lifestyle.
Here are some sample calculations …
Example 1.1 : Long haul large plane flights
Let us consider a fully loaded Boeing 777 …
Fuel consumption = 7500 kilograms per hour.
We assume that all of that 100% of the fuel is converted into carbon dioxide.
Cruising speed = 1000 kilometres per hour.
Carbon emissions = 7500/1000 = 7.5 kilograms per kilometre.
Total payload = 212 tonnes
Passengers = 340 people = 39 tonnes (18%)
Cargo = 173 tonnes (82%)
Emissions = (7.5 x 18%) / 340 = 0.00397 kilograms per person per kilometre
Let us consider a flight from New York to Johannesburg …
Distance = 12820 kilometres
Return distance = 25640 kilometres
Emissions = 25640 x 0.00397 = 100 kilograms per person
Let us offset these emissions using our tropical super-trees …
Carbon sequestration = 10 kilograms per tree per year
Offsetting requirement = 10 trees
Estimated cost = USD 40
If you spend just USD 40 to plant ten trees, they will be able to absorb enough carbon to enable you to fly between New York and Johannesburg and back every year for the next 40 years.
Example 1.2 : Short haul small plane flights
Let us consider a fully loaded Cessna 206 …
Fuel consumption = 100 kilograms per hour.
We assume that all of that 100% of the fuel is converted into carbon dioxide.
Cruising speed = 260 kilometres per hour.
Carbon emissions = 100/260 = 0.38 kilograms per kilometre.
Passengers = 4 people
Emissions = 0.38 / 4 = 0.096 kilograms per person per kilometre
Let us consider a flight from Gaberone to Kasane …
Distance = 150 kilometres
Return distance = 300 kilometres
Emissions = 300 x 0.096 = 29 kilograms per person
Let us offset these emissions using our tropical super-trees …
Carbon sequestration = 10 kilograms per tree per year
Offsetting requirement = 3 trees
Estimated cost = USD 12
If you spend just USD 12 to plant three trees, they will be able to absorb enough carbon to enable you to fly between Gaberone to Kasane and back every year for the next 40 years.
Road travel
When it comes to road travel, we need to take into account both the emissions created by running your vehicle and the carbon cost of manufacturing it in the first place …
Example 1 : Medium-sized petrol car : 127 trees
Let us consider a modern medium-sized vehicle, starting with the fuel consumption under typical usage …
Fuel efficiency = 20.5 km per litre (49 mpg)
Fuel consumption = 1 / 20.5 = 0.0489 litres per kilometre
Specific mass of petrol = 0.74
Fuel consumption = 0.0489 x 0.74 = 0.0361 kilograms per kilometre
We assume that all of that 100% of the fuel is converted into carbon dioxide.
Carbon emissions = 0.0361 kilograms per kilometre
Annual journey total = 18,500 km (11,500 miles)
Annual fuel consumption = 18500 x 0.0361 = 667 kilograms of carbon per year
Now let us look at the cost of manufacture and maintenance (the numbers being taken for a Ford Mondeo) …
Production emissions = 17,000 kilograms of carbon dioxide
Proportion of carbon in carbon dioxide = 0.27
Production emissions = 17,000 x 0.27 = 4590 kilograms of carbon
Vehicle lifespan = 12 years
Production emissions = 4590 / 12 = 382 kilograms of carbon per year
Maintenance emissions @ 10% = 382 x 0.1 = 38 kilograms of carbon per year
Total product emissions = 420 kilograms of carbon per year
Total vehicle emissions = 1087 kilograms of carbon per year
Let us offset these emissions using our tropical super-trees …
Carbon sequestration = 10 kilograms per tree per year
Offsetting requirement = 109 trees
Estimated cost = USD 436
If you spend just USD 436 to plant 109 trees, they will be able to absorb enough carbon to enable you to drive a medium-sized car for the next 40 years.
