Every schoolchild knows that the tree absorbs CO2 and emits O2. Therefore the discussion of tree planting seems curiously absent from measures to curb the rise of CO2 in the atmosphere, instead any debate about carbon reduction centres around large scale geo-engineering.
On the face of it trees have many advantages over carbon removal technologies;
Trees already exist
They are cheap
They don’t mess up the environment (Some might even say they improve it)
They are (currently) not operated by a large corporation determined to monetize climate tragedy
So for the tree to come to the rescue we need to understand the scale at which trees would need to be implemented to offset the actions of man, generally expressed in the act of burning.
The total mass of the atmosphere is 5.1e18 kg.
At the beginning of 2016 the carbon dioxide content of the atmosphere was 403ppm. So the mass of carbon dioxide in the atmosphere, assuming an equivalent density to air (its actually a bit denser) was:
5.1e18 x 403 / 1000000 = 2.055 e15 kg.
The amount of carbon dioxide that a tree can remove and store varies widely by species and climate region etc. The figure used here is 50 pounds of carbon dioxide per annum (22.7 kgs for real scientists).
The rate at which the carbon content of the atmosphere is increasing can be determined from the previous reference between the years 2012 (393ppm) and 2016 (403ppm) or 2.5ppm per year. So, in order to stabilise the measured trend one would need to annually remove the same amount.
2.5ppm or 2.055e15 x 2.5 / 403 = 1.275e13 kg of carbon dioxide.
This would require 1.275e13 / 22.7 = 5.615e11 trees.
So what sort of land coverage would this many trees take up? Using the value of 500 trees per hectare for 70 year old woodland (the upper value of the range suggested in the link to account for the transition from denser newly planted to less dense mature woodland) That would give a required coverage of
5.615e11 / 500 = 1.123e9 Hectares or 11.23 million sq km
This is about 10% greater than the land mass of Canada. (which already has a lot of trees). The estimated forest coverage of the planet land mass is 30%, therefore of the remaining land mass, from a total of 130.56million sq km , 91.39 million sq km is not forested. In order to stabilise the rate of carbon dioxide increase in the atmosphere, before even thinking about reducing it, the unforested land mass of the Earth would have to be 12.5% covered with trees.
While we decide whether this is a plausible solution or not, it might be a good idea to stop chopping them down.