This doesn’t mean humanity is doomed, provided the predictive model is reasonably accurate. However, it does reinforce the idea that any solution to emissions reduction is likely to be complex, and will usually involve a lot more than planting greenery.
For the researchers, this includes both reducing fossil fuel consumption and implementing multiple techniques for lowering CO2 levels beyond planting trees. You could make more efficient use of available land by eliminating food waste, as an example. Reforestation is still wise, but it’s just one piece in a larger puzzle that can include everything from smarter farming to solar power.