Not to discourage, but even reforesting entire land that could possibly be covered in forest will not arrest climate change noticeably.

The reason is because forest do not change CO2 levels noticeably, in the long run. The reason is because there is roughly constant amount of carbon in Earths biomass. Planting treas only increases the amonut of biomass by a little bit but has no lasting effect of scrubbing CO2 from atmosphere.

The real solution to climate change is undoing decades of constant addition of CO2 to atmosphere. This requires not only scrubbing CO2 from atmosphere but also sequestering the carbon somehow which means preventing it getting back to carbon cycle.

If you really wanted to make planting trees have an effect you would not only need to plant trees, you would need to regularly cut them (before they burn) and store them somewhere, maybe at the bottom of ocean, from where it will not be released (decomposed, burned, etc.)

Of course, planting trees have other beneficial effects like helping to keep rainwater. It is just important to make sure right kinds of trees (and large variety of them!) are planted to not repeat mistakes that were made in other places.