<p>Reforestation is considered an important nature-based climate solution to help achieve net-zero CO₂ emissions. However, strategies using reforestation-based CO₂ removal to offset fossil fuel emissions may not lead to the same climate outcome as avoiding the fossil fuel emissions. Here, we use an Earth System model of intermediate complexity to compare the climate outcome of different pathways: a reference pathway, and net-zero pathways where additional fossil fuel CO₂ emissions relative to the reference pathway are balanced by reforestation-based CO₂ removals (“Reforestation Net-zero pathways”). Results show that model simulations of Reforestation Net-zero pathways yield a higher atmospheric CO₂ and warmer climate outcome than the reference simulation. The higher atmospheric CO₂ results from carbon cycle feedbacks. The additional global warming from higher atmospheric CO₂ is further amplified by biogeophysical effects of reforestation. These findings highlight the need for improved methods to account for the carbon cycle and climate effects of reforestation.</p>