Uncertain Global Terrestrial Carbon Cycles Complicate the Predictability of Global Energy Transition Pathways

The Paris Agreement aims to combat climate change by limiting global temperature rise to well below 2°C, with aspirations of reducing it to 1.5°C by the end of the century. However, debates are intensifying over the pace and direction of energy transitions needed to meet these goals. Our study highlights significant uncertainties in the terrestrial carbon cycle and their implications for mitigation efforts and energy transition pathways. We used the results from the TRENDY Model-Intercomparison Project to represent terrestrial carbon cycle simulations from 11 models using the Hector model, the simple climate model coupled to a multisector integrated assessment model, the Global Change Analysis Model. Focusing on scenarios limiting global warming to 1.5°C by the end of the century, we assessed the uncertainties in energy trajectories and associated carbon prices. Our results reveal that uncertainties in terrestrial carbon cycle projections meaningfully affect the pace of global energy transitions to meet climate policy goals. The models predict the phase-out of unabated coal power generation by 2050 ± 7 years. Additionally, ensemble simulations estimate a carbon price of 170.25 ± 38.84 $/tCO2e in 2010$ by the end of the century. Our findings highlight the critical need to refine models and integrate updated data to improve the reliability of carbon cycle projections and guide effective climate policy development. Specifically, enhancing the representation of the terrestrial carbon cycle in integrated assessment models is essential. Addressing these uncertainties is crucial for informed decision-making and effective implementation of strategies to achieve long-term climate objectives.