Fig. 1: Required CO₂ emission intensity (tonne of CO₂/ tonne of crude steel) with the decreasing budget for the 2 °C climate target versus increasing outputs of crude steel and pig iron globally from 2020 to 2050.

The emission scenario in the iron and steel sector for the 2 °C target (green colour) is set from the International Energy Agency (IEA), which mainly considers short-term energy efficiency improvements and scrap-based electric arc furnace (scrap/EAF) and carbon capture and storage (CCS) in the mid- to long-term^4,5. The outputs of crude steel and pig iron in 2015–2019 (orange bars) are obtained from the World Steel Association (WSA)¹⁷, while those in 2020–2050 (solid lines) are estimated based on the production scenario given by the United Nations Industrial Development Organization (UNIDO), which mainly considers the strong demand growth in non-OECD countries such as BRICS and ASEAN^5,6. The future iron and steel outputs could be different from those estimated by UNIDO and therefore, the effect of iron and steel outputs on the potential CO₂ emission reduction is further discussed in the potential sensitivity analysis (section: decarbonisation pathways for the iron and steel sector). The CO₂ emission intensity is calculated based on sectorial scenarios given by the IEA^4,5 and the production scenario of crude steel and pig iron given by the WSA¹⁷ and UNIDO^5,6.