Abstract:
Carbon dioxide removal (CDR) is crucial to achieving the temperature targets of the Paris Climate Agreement by the end of this century. After CDR application, global surface temperatures are expected to peak in the subsequent years. However, the limited number of models in the Coupled Model Intercomparison Project phase 6 (CMIP6) that conducted CDR simulations hampers our understanding of when global surface temperature peaks under CDR scenarios. Herein, a two-layer Energy Balance Model (EBM) based on the forced response framework is found to reasonably capture the impact of changes in atmospheric CO
2 concentration on global surface temperatures and the timing of their peak following CDR application. This model can complement CMIP6 CDR simulations and serve as a tool to investigate the factors influencing the timing of the temperature peaks. The EBM results suggest that in scenarios excluding the deep ocean, the equilibrium climate sensitivity affects how soon after CDR initiation temperature peaks occur, with the Earth’s surface heat capacity also playing a role. When the deep ocean is present, its heat capacity demonstrates the greatest contribution, followed by equilibrium climate sensitivity and then Earth’s surface heat capacity. These factors primarily affect the timing of global surface temperature peaks by altering the magnitude of the surface energy imbalance when CDR starts. Compared to scenarios excluding deep ocean, incorporating it slightly advances the timing of temperature peaks and reinforces the contribution of CO
2 forcing in reducing the magnitude of net energy flux at the Earth’s surface when CDR starts.