Structural uncertainty in the direct human forcing of future global burned area

The first fire model intercomparison project (FIREMIP) gave rise to two distinct proposals around how best to improve the fire modules of dynamic global vegetation models. The first proposal was to develop representation of direct human impacts on burned area, particularly managed fire use in agriculture and other land management. The second proposal was to improve representation of the ecological dimensions of fire, including relationships of fuel load, connectivity, dryness and fire. Here, we present future projections from two models that have attempted to advance model representation and understanding of the human (WHAM-INFERNO) and ecological (Haas) dimensions of global fire regimes. The models project radically different future burned area for the same sets of scenario forcings. There is particularly strong disagreement regarding direct human impacts (or “direct human forcing”) of global burned area: differences in model assessment of the impact of direct human forcing is greater between models than between scenarios. We show how such structural uncertainty constrains understanding of climate change adaptation, including its limits and pitfalls. Differences in model outputs are largely traceable back to model assumptions. Hence, we argue that advances made by the two models could be combined in a future fire model that better captures the socio-economic and ecological drivers of burned area. We identify key challenges to the development of such integrated socio-ecological models, highlighting crucial uncertainties around how anthropogenic and biophysical factors interact to produce patterns of fuel fragmentation and hence fire spread. Overall, advancing understanding of the interactions between human and biophysical drivers of fire remains a central challenge in fire science.