Recycled steel is a key material for sustainable development. However, not all steel demand can be met by recycling, and therefore, new metallic iron must be introduced in the global cycle. The transformation of iron oxides into steel requires carbon which is oxidized into CO. This paper focuses on the basic oxygen furnace (BOF) where molten iron is converted into liquid steel. In order to assess the effect of molten iron temperature on CO emissions, the process has been modelled using mass and energy balances. Model results show that, for a typical converter charge, a slight increase of 10 °C can lead to a direct reduction of 0.006 t of CO per ton of liquid steel. A total variation of 0.17 t of CO per ton of liquid steel is found depending on plant strategy and process constraints. Finally, different actuation levers for carbon mitigation are assessed. It can be concluded that operation and modelling improvements should be jointly addressed to exploit their full potential for carbon footprint reduction.