$5/tonne for forestation? I did the numbers - some time ago so my memory is hazy at best - but I'm pretty sure we ended up at one big tree being roughly one tonne of carbon, and big trees are not five dollars a pop. Have we not included the cost of the land?
Forestation can be quite controversial so we err very heavily on the safe side. Our calculation is on the site[1] but I'll copy it here for clarity as well:
* We use an average CO₂ sequestration rate of 10.875kg of CO₂/tree/year.
* We only take the first 5 years of the trees' carbon sequestration into account. What gets sequestered after this is a gift to our planet and we don’t sell that.
* To mitigate chances of loss due to disease or fires we double plant (meaning we buy double the number of trees that we need to).
Therefore for every two trees we purchase we assign a removal value of 54.375kg (10.875kg * 5 years).
For one tonne of carbon that is (1000kg / 54.375kg) * 2 trees = 37 trees (rounded). At $0.15 per tree that's $5.5.
