Last year in 2018, the world emitted an estimated 37 billion tonnes of Carbon Dioxide. If you compressed all that back into coal or graphite, you’d have about 6 semi-trucks full of coal for each person in the world. That’s tons of carbon. How many trees would we need to grow to offset that for both current and future carbon emissions? Let’s dive into the numbers.
Trees have this amazing ability of being almost entirely made up of carbon atoms. They need very few nutrients relative to their size so they don’t deplete the topsoil, get most of their water from deep underground, and their mass from the air they breathe. This means that the lifetime carbon value of a tree, the total amount of carbon it will absorb, is about the same as its mass. Again, this is Carbon the atom. Not Carbon Dioxide the molecule (we’ll have to do some conversion of atomic weights to arrive at the real number later on).
So what’s the average mass of a tree? About 2 tonnes. Does that mean we need to plant 19 billion trees per year to offset our Carbon Dioxide emissions? Here’s the good news. Since photosynthesis takes in Carbon Dioxide (CO2) and releases all of the Oxygen (O2), we only need to take the weight of the Carbon atoms and subtract all of the Oxygen molecules away from the weight of each tree. So 2 tonnes of tree matter actually removes about 7 tonnes of Carbon Dioxide by converting the rest to Oxygen.
- The math:
2 tonnes / (12 / 44) = 7.33, where 12 / 44 comes from the relative weight of the Carbon atom in each molecule of Carbon Dioxide.
Since each tree will remove 7 tons of Carbon Dioxide, we would need to plant about 5 billion trees per year to account for current emission levels.
But wait! We are missing one key variable. We have calculated mass, but we haven’t taken into account time.
Trees take a very long time to grow, and it’s likely that our carbon emissions will continue to go up as the world continues to grow and develop. This means that in order to take into account future growth of carbon emissions, each person would need to plant one tree per year, every year, for each year they’ve been alive and continue to live.
Even if everyone were to do this, the effects of planting each new tree won’t be felt in terms of offsetting the emissions until the tree is fully grown, which could take dozens of years. This is why we need a different solution, even though planting new trees is definitely a viable way to supplement existing efforts.
Time to start saving up some land…