PNNL

Abstract

Most of the integrated assessment modeling scenarios being used to inform international efforts to meet ambitious climate targets now rely on large-scale deployments of negative emissions technologies (NETs). Here we use the Global Change Assessment Model (GCAM) to conduct a detailed assessment of tradeoffs between global food, water, and energy for a portfolio of NETs and mitigation options that includes direct air capture (DAC) technology. We find that DAC could provide up to 3 GtCO2-yr-1 of negative emissions by 2035 based on current-day assumptions regarding price and performance. DAC deployment is dominated by regions such as the U.S. and China with abundant geologic carbon storage capacity and inexpensive natural gas resources. While this deployment of DAC would reduce land use demand for bioenergy with carbon capture and storage and afforestation, it could also exacerbate demand for energy and water. DAC process heat reaches 16 EJ-yr-1 by 2035, over 12% of current-day natural gas demand. At a global level, reductions in water withdrawals and consumption for BECCS may be offset, in whole or in part by DAC itself. Impacts (e.g., food price increases) of BECCS and afforestation, while attenuated by DAC, remain concentrated predominantly in the Global South. Negative emissions requirements are driven largely by sectors recalcitrant to decarbonization, pointing to the need to reduce gross, as well as net CO2 emissions to reduce the tradeoffs of all NETs. We emphasize that the precondition for all our scenarios is aggressive, near-term global decarbonization policy to limit overdraft of a rapidly diminishing emissions budget consistent with a below-1.5°C future. Delays in such aggressive global mitigation action greatly increase the requirement for DAC to meet the same end-of-century temperature goal, and correspondingly, energy and water impacts.