Can reforestation help stabilize the climate in net-zero pathways?

Reforestation is a nature-based climate solution (NbCS) that can serve to sequester and store large quantities of atmospheric carbon dioxide. It requires no new technological advancements for deployment, is relatively cost-effective, and it would lead to important co-benefits for ecosystems and ecosystem services. For these reasons reforestation is a key measure in deep-mitigation and net-zero pathways. However, reforestation at scale alters land-surface biophysical properties (albedo, evapotranspiration and latent heat release, and sensible heat flux) that can induce either a warming or cooling effect on  surface temperature. The magnitude and sign of this temperature response depend on the background climate state and latitude over which reforestation is implemented. Therefore, depending on the scale and region of reforestation, these biophysical effects could lead to additional warming in emission pathways that use reforestation to compensate for residual CO₂ emissions. 

Our research investigates the effectiveness of reforestation at stabilizing global mean temperature when used to compensate for residual CO₂ emissions. Using a climate model of intermediate complexity (the UVic-ESCM v2.10) we conduct a set of idealized simulations where fossil fuel emissions decline towards zero by 2050 but remain at 1 and 5, Gt CO₂/yr between 2050 to 2100 to represent emissions that are difficult to eliminate. Meanwhile reforestation is implemented globally and in different latitudinal zones (tropics, mid-latitudes, and high-latitudes) at an areal coverage appropriate to sequester the ongoing emissions so that cumulative CO₂ emissions between 2050 and 2100 are net-zero. From these simulations we quantify the effectiveness of reforestation at stabilizing global mean temperature under consideration of biogeochemical and biophysical effects and feedbacks. 

While we expect our results to show that the carbon sequestration from reforestation could be effective at stabilizing global mean temperature, the biophysical effects could also induce important variations in global mean temperature. As such, our research is intended to provide an Earth system analysis of reforestation that can inform forestation carbon markets and net-zero policy frameworks.