The problem is that the carbon cycle is pretty much closed at the plant side. They create O2, but during burning, rotting or other biological activity it gets t

The problem is that the carbon cycle is pretty much closed at the plant side. They create O2, but during burning, rotting or other biological activity it gets transformed into C02 again. You can see this in the data - during the northern hemisphere winter CO2 goes up, during summer it goes down. There's also a similar day-night cycle. What happens then is that more CO2 is added, and it seems to be clear at this point that the plants are not keeping up - even losing ground due to land use change and deforestation. Main carbon sinks are ocean uptake (the problem discussed in the article), weathering and the small amounts of organic matter that sink below the ground/sea/lakes without rotting (and which will create new coal and oil in time). Apart from the first point, these processes happen on geologic time scales. (Also, shells of small sea animals, but again a miniscule factor. Those will be the next lime rocks.) What you suggest is a new sink for carbon. However, it would probably cost more energy than can be gotten from fossil fuels because gravity. (Sry, too tired to run the calculations right now.)