Reconciling Integrated Assessment Estimates of Carbon Removal with Regional-Scale Potential

Countries are increasingly announcing plans to achieve net-zero emissions by mid-century. Recalcitrant emissions from the transportation, industrial, and building sectors make it extremely difficult to achieve these goals without significant deployments of carbon dioxide removal (CDR). The Integrated Assessment Models widely used by the international community to study decarbonization pathways increasingly rely on significant deployments of CDR even though these technologies are largely unproven. Here, we use the Global Change Analysis Model for the United States (GCAM-USA) to understand how it would achieve net zero targets for one US State; Virginia. Virginia is a representative case study because it is a mid-sized state with a diversified economy and the first in the US South to set a net zero target. We studied the conditions under which three representative forms of negative emissions: afforestation, bioenergy with carbon capture, and direct air capture are deployed to offset the states recalcitrant emissions in GCAM-USA. Our modeling results are then compared with ground-up estimates of afforestation and other forms of natural carbon removal. Our analyses suggest significant disparities between top down and bottom up estimates of CDR potential. In the context of Virginia GCAM-USA tends to underestimate the amount of natural carbon removal that is possible. The model is heavily focused on deploying bioenergy with carbon capture at a scale that would introduce profound tradeoffs in the rural communities that would support this activity. The impacts on regional air quality, economic markets, nutrient cycling, and water quality associated with BECCS and afforestation in particular, as well as community priorities around things such a protection of subsurface water sources, call into question the practical viability of global scale models that assume too much about how much CDR could be possible at the regional scale.