The climate implications of failing to manage carbon

In scenarios that limit the increase in global mean temperature (GMT) this century to 1.5 or 2°C, large quantities of carbon are managed by both carbon capture and storage (CCS) at point sources and atmospheric carbon dioxide removal (CDR). Such carbon management may be used to offset ongoing (“residual”) emissions from hard-to-abate sectors and to decrease the concentration of carbon dioxide in the atmosphere if various feasibility and sustainability challenges are overcome. Here, in over 16 million simulations of the simple climate model MAGICC, we systematically analyze the climate implications of failing to manage carbon to the degree called for in 407 different climate mitigation scenarios. We find that entirely failing to manage carbon relates to ~0.5°C higher GMT in 2100, making it impossible to meet the 1.5°C target, but leaving 2°C in reach this century–assuming the projected decreases in emissions still occur. Our results also show that peak temperatures are especially sensitive to land-based CDR (afforestation and reforestation) that often ramps up quickly in the scenarios, whereas end-of-century temperatures depend more on levels of engineered CDR (bioenergy with carbon capture and storage, direct air capture with storage). What is clear, though, is that the quantity of carbon in avoided emissions is vastly larger than carbon managed in every climate mitigation scenario.