First of all, the purpose of photosynthesis is primarily for obtaining energy via carbon. Oxygen by itself is no use. Secondly, not all of the oxygen that a pla

First of all, the purpose of photosynthesis is primarily for obtaining energy via carbon. Oxygen by itself is no use. Secondly, not all of the oxygen that a plant uses comes from photosynthesis. Some of it can be absorbed from water in the roots, and some is absorbed from the air itself between cells. The amount varies from species to species. More importantly, you've completely missed the bigger point. Carbon has been sequestered from the atmosphere over millions of years. Now we are releasing that carbon at a high rate over a few decades. The balance is being changed at an extremely fast rate, in a blink of a geological eye. So.... the OP originally tried to justify fossil fuels on the basis that plants will just absorb it. Can you answer my question to them? Where does that carbon go once a plant has absorbed it? Ok, so let me cut to the chase. Plants store the carbon. Plants eventually die. Carbon is mostly released back into the atmosphere either indirectly or directly. So increased plant sequestration is only a temporarily store, it can't help us fix the carbon issue permanently.