Slicing the pie: how big could carbon dioxide removal be?

The current global dependence on fossil fuels to meet energy needs continues to increase. If a 2 degrees C warming by 2100 is to be prevented, it will become important to adopt strategies that not only avoid CO2 emissions but also allow for the direct removal of CO2 from the atmosphere, enabling the intervention of climate change. The primary direct removal methods discussed in this review include land management and mineral carbonation in addition to bioenergy and direct air capture with carbon capture and reliable storage. These methods are discussed in detail, and their potential for CO2 removal is assessed. The global upper bound for annual CO2 removal was estimated to be 12, 10, 6, and 5 GtCO(2)/year for bioenergy with carbon capture and reliable storage (BECCS), direct air capture with reliable storage (DACS), land management, and mineral carbonation, respectively-giving a cumulative value of similar to 35 GtCO(2)/year. However, in the case of DACS, global data on the overlap of low-emission energy sources and reliable CO2 storage opportunities-set as a qualification for DAC viability-were unavailable, and the potential upper bound estimate is thus considered conservative. The upper bounds on the costs associated with the direct CO2 removal methods varied from approximately $ 100/ tCO(2) (land management, BECCS, and mineral carbonation) to $ 1000/tCO(2) for DACS (again, these are the upper bounds for costs). In this review, these direct CO2 removal technologies are found to be technically viable and are potentially important options in preventing 2 degrees C warming by 2100. (C) 2017 Wiley Periodicals, Inc.