Land-Use Change, No-Net-Loss Policies, and Effects on Carbon Dioxide Removals

Carbon dioxide removal (CDR) from the atmosphere, a critical component of all strategies for restricting global warming to 1.5°C, is expected to come largely from the continued sequestration of carbon in vegetation, mainly in forests. Because CDR rates have been declining in the United States, in part from land-use changes, policy proposals focus on altering land uses through afforestation, avoided deforestation, and no-net-loss strategies. Estimating policy effects on CDR requires a careful assessment of how land-use change interacts with forest conditions.

Using a model of land-sector emissions that mirror inventories generated by the US government, we evaluate how alternative specifications of land-use change in the United States affect projections of CDR. Without land-use change, CDR declines from 0.826 gigatons (GT) per year in 2017 to 0.596 GT/year in 2062 (–28 percent) because of the aging and disturbance of forest vegetation. With a land-use scenario that extends recent rates of change, we contrast CDR estimates for a case where only net changes in forest area or carbon stocks are tracked with estimates that separately take account of forest losses and forest gains. The net change approach underestimates the CDR effects of land-use change by about 56 percent. We also compare long-run CDR losses from deforestation with gains from afforestation per unit area and find that afforestation gains lag deforestation losses in every US ecological province. Planted forests accelerate CDR benefits over naturally regenerated forests in the Southeast and Pacific Coast regions.

Net change approaches substantially underestimate the effects of land-use change on CDR and should be avoided. We show that avoided deforestation provides up to twice as much CDR benefit as increased afforestation. The disparities in the CDR effects of afforestation and deforestation indicate that no-net-loss policies could mitigate some CDR losses but would likely lead to overall declines in CDR for our 45-year time horizon. Over a longer period, afforestation could offset more of the losses from deforestation but on a timeframe inconsistent with most climate change policy efforts.