I want to do a thought experiment, hoping not to make any mistake.
The world produces 29,888,121,000 metric tons of CO2 per year. According to Wikipedia, one ton of dry wood sequestrates 1.8 tons of CO2. If you put these two together, you quickly realize that you need to produce 16,604,511,666 tons of wood per year in order to offset the worldwide CO2 production.
The largest single stem tree available today is the General Sherman giant sequoia. It is 83.8 meters tall, with a diameter of 7 meters. Its estimated dry weight is 1121 tons. It took thousands of years to reach that size, and it’s a unique tree, but I will use it as a greatly exaggerated upper limit to the size and mass of a tree. I estimate a normal tree as a fifth of that, or 250 tons. In order to compensate the CO2 emission, we need to plant and grow to full size 66 millions trees. Assuming the tree occupies an area of 10 x 10 square meter this adds up to a required forest size of 6600 square kilometers, which is one sixth of Switzerland. Every year.
Of course, I am not considering the fact that a tree must grow to full size in order to offset the CO2. If we do, and if we assume it takes 20 years for a tree to reach the size given above, we need to plant a little more than three Switzerlands of trees right now, to offset the CO2 production of the next 20 years, for a grand total of 1.3 billion trees. Considering the population of Europe is 852 million people, it means that each of us needs to plant a little more than one tree.
I’m working on that. And you ?