1. On the basis of latitude and longitude, the shortest distance between departure and arrival airport is calculated using the greater circle distance calculation formula.
2. The greater circle distance (shortest distance) between departure and arrival airport is then multiplied by a detour factor, to account for holding patterns, weather conditions etc.
3. To calculate fuel consumption, a weighted mean (using EU passenger data) of the consumption of 3 aircraft types in the case of short-haul flights (<1,000 nm) and 4 aircraft types in the case of long-haul flights.
4. The fuel consumption is then converted to CO2 emissions by multiplying by 3.15.
5. To calculate the CO2 emissions per passenger, the average number of seats in short and long-haul flights, the average load factor (percentage of seats filled) and a factor for flight class (economy, business, first) are drawn upon.
6. Finally the CO2 emissions per passenger are multiplied by the factor 2, to account for CO2-equivalents and the height at which the emissions take place.
You can download the detailed calculation of flight CO2 emissions here.
This is how the storage of CO2 in biomass is calculated:
1. To ascertain the level of growth of an area being reforested, several test areas are selected and samples taken. In the test areas, every tree trunk (with a diameter of more than 5cm) is measured in chest height. Such inventories are repeated every 5 to 10 years and the additional biomass is calculated. The inventory also calculates the removal of wood.
2. The inventory only measures the tree trunk. To calculate the entire biomass on the basis of the tree trunk the so-called biomass expansion factor is used. These factors have been extensively researched (for many common types of tree) and are published i.a. by IPCC. The biomass expansion factor also accounts for subterranean biomass in the form of roots.
3. The entire biomass is the multiplied by the specific wood density (in this case 0.46 t/ m³) to calculate the dry mass of the wood.
4. 50% of wooden dry mass consists of carbon. Wood and biomass grows by the process if photosynthesis, in which CO2 is taken from the air and with a combination of sunlight and water forms wood and biomass. As such, the wooden dry mass is multiplied by 0.5 to calculate the amount of carbon stored.
5. To convert carbon into carbon dioxide (CO2), a factor of 3.667 is applied.
You can download the detailed calculation of CO2 storage in biomass here (german).