Global warming is a serious problem, and we are often given ways we can help. Most of those methods involve reducing our contributions to the problem. Occasionally, something like planting a tree is mentioned, a far better activity for a growing tree reduces greenhouse gases.
Simply put, the main focus is on greenhouse gases, especially carbon dioxide. But the fact we reduce adding carbon dioxide does little for taking any carbon dioxide out of the atmosphere. Our main ally in reducing carbon dioxide is the trees. Yes, when there is more carbon dioxide the trees might flourish, and remove more carbon dioxide than they might otherwise, but it is not nearly enough.
So, even if we stop adding to the problem, the reversal will be slow. But, not adding to the problem is a necessary first step.