Carbon-climate feedbacks to spatial aerosol model implementation variations

Aerosols have played an important role in defining climate development over the historical period, due to their cooling impact in the atmosphere. However, as their emissions are expected to decrease in the upcoming decades, and therefore also their cooling effect, they will likely be associated with the future warming of the planet. Despite their importance, and the high uncertainty of their radiative forcing, aerosols inclusion or consideration in, for example, simple climate models, integrated assessment models and carbon metrics requires extensive simplifications and assumptions. Typically, interactions between physical and biogeochemical processes, as well as triggered feedbacks, are disregarded by such models and metrics, which is a potential further source of uncertainty in the aerosols’ led responses in a changing climate. By varying the spatial implementation of aerosols in an intermediate complexity model, we explore the variability in Earth system responses under a highly ambitious mitigation scenario due to a change in aerosols forcing. When spatial heterogeneities in forcing are disregarded, surface air temperature development can differ by almost 0.1°C, which would correspond to an approximate uncertainty of 200 GtCO ₂ in estimates of remaining carbon budgets. The warming and cooling contributions of different Earth system processes, such as land carbon uptake or ocean heat uptake, are also seen to vary strongly depending on the spatial distribution of aerosols in the atmosphere. The main processes driving these responses are found to be land surface temperature and its impact on soil respiration, as well as ocean ventilation processes and sea ice cover changes. These findings highlight that the spatial distribution of aerosols is capable of triggering important climate feedbacks, which should not be disregarded when assessing climate development and simulated Earth system responses. These feedbacks will be instrumental in defining potential pathways for temperature stabilisation and evaluating, for example, remaining carbon budgets.