The full climate impacts of nature-based climate solutions must be considered to achieve climate goals

Nature-based climate solutions (NBCSs) refer to actions that seek to protect, restore and better manage natural landscapes to reduce greenhouse gas (GHG) emission or remove CO₂ from the atmosphere. NBCSs are integral part of many countries’ roadmaps to reach net zero GHG emissions by mid century in compliance with the Paris Agreement climate goals. Implementation of NBCSs not only affects cycling of CO₂ and other GHGs in the Earth system, but impacts the energy balance at the Earth’s surface through biophysical effects including changes in reflectivity (albedo), surface roughness and the water cycle, with effects on surface temperature. Furthermore, storage of the sequestered CO₂ in above-ground biomass is often vulnerable to natural and anthropogenic disturbances, with the risk of re-release after a few decades. Yet, frameworks that seek to balance residual GHG emissions with nature-based CO₂ removal often only consider the CO₂ sequestration potential, and do not take the full climate impacts of NBCSs and the vulnerability of carbon stocks into account. By implementing large-scale reforestation as an example of a NBCS in an Earth system model we show that offsetting fossil-fuel CO₂ emissions with nature-based CO₂ removals to achieve net zero CO₂ emissions could result in additional warming compared to the case where the CO₂ emissions are avoided, if biophysical effects are not considered and nature-based CO₂ storage is temporary. We provide recommendations for taking into account the full climate impacts of NBCSs in net zero accounting frameworks and lay out directions for future research.