Hysteresis of fire-prone weather to CO2 forcing

CO₂ emission from biomass burning (BB) is one of the essential elements of the global carbon budget, with its annual mean of about 2.0 PgC/year equivalent to 15 % of 2020 fossil fuel emissions. However, while a global increase in fire-prone weather is projected alongside climate change, a quantitative understanding of how much carbon will further be released due to increased fires is highly limited, which could result in large uncertainty in meeting the net zero target. Thus, in this study, we evaluate future changes in fire-prone weather based on the fire weather index (FWI) and estimate the potential fire-induced emissions on a global scale that could be induced by climate change. To this end, 28 ensembles of idealized CO₂ reduction simulations with the CESM climate model were analyzed. The results show that when CO₂ in the atmosphere is doubled (2xCO₂) from 367 ppm by 1 % per year, the additional emission due to increased fire weather could reach about 1.7 PgC/year, which corresponds to 82% of the current BB emission. Moreover, even if the atmospheric CO₂ concentration further peaks and is reduced back to 2xCO₂, the lagged response of the climate system can cause fire-prone weather and its resulting C emissions to remain higher than its previous state in many countries. These results highlight that more focus is required on the climate-fire-carbon feedback not only for more accurate future predictions but also for achieving net zero emissions in each country through a proper wildfire management strategy.