Negative emissions—Part 2: Costs, potentials and side effects

TLDR

The IPCC highlights negative emissions technologies as cost‑effective means to limit warming to 2 °C, yet a comprehensive, transparent literature review of CO₂ removal options is lacking. This review aims to estimate costs, potentials, and side‑effects of seven NETs and assess their viability. The authors conduct a systematic literature review of seven NETs—BECCS, afforestation, DACCS, enhanced weathering, ocean fertilisation, biochar, and soil carbon sequestration—to estimate costs, potentials, and side‑effects. Their estimates indicate sustainable global NET potentials in 2050 ranging from 0.5 to 5 GtCO₂ yr⁻¹ across technologies, with wide cost variability and limited permanence, suggesting no single NET can meet the carbon uptake rates required for 1.5 °C pathways.

Abstract

The most recent IPCC assessment has shown an important role for negative emissions technologies (NETs) in limiting global warming to 2 °C cost-effectively. However, a bottom-up, systematic, reproducible, and transparent literature assessment of the different options to remove CO2 from the atmosphere is currently missing. In part 1 of this three-part review on NETs, we assemble a comprehensive set of the relevant literature so far published, focusing on seven technologies: bioenergy with carbon capture and storage (BECCS), afforestation and reforestation, direct air carbon capture and storage (DACCS), enhanced weathering, ocean fertilisation, biochar, and soil carbon sequestration. In this part, part 2 of the review, we present estimates of costs, potentials, and side-effects for these technologies, and qualify them with the authors' assessment. Part 3 reviews the innovation and scaling challenges that must be addressed to realise NETs deployment as a viable climate mitigation strategy. Based on a systematic review of the literature, our best estimates for sustainable global NET potentials in 2050 are 0.5–3.6 GtCO2 yr−1 for afforestation and reforestation, 0.5–5 GtCO2 yr−1 for BECCS, 0.5–2 GtCO2 yr−1 for biochar, 2–4 GtCO2 yr−1 for enhanced weathering, 0.5–5 GtCO2 yr−1 for DACCS, and up to 5 GtCO2 yr−1 for soil carbon sequestration. Costs vary widely across the technologies, as do their permanency and cumulative potentials beyond 2050. It is unlikely that a single NET will be able to sustainably meet the rates of carbon uptake described in integrated assessment pathways consistent with 1.5 °C of global warming.