Carbon–climate feedback higher when assuming Michaelis–Menten kinetics of respiration

Earth system models simplify complex terrestrial respiration processes assuming a first-order chemical reaction or assuming a Michaelis–Menten kinetics. The effect of the respective mathematical representation on the terrestrial carbon–climate feedback is unclear. Using a simplified model of biogeochemical feedbacks to climate, I show that the terrestrial carbon–climate feedback roughly doubles when assuming Michaelis–Menten kinetics of respiration. Consequently, the remaining carbon budget to keep global warming below 2 °C is substantially higher. The effects of the respiration formulation also depend on the underlying emission scenario. These results highlight the importance of an increased understanding of the respiration processes on a global scale to more reliably project future carbon dynamics and climate and related feedback mechanisms and thus to estimate a valid remaining anthropogenic carbon budget using Earth system models.