Although the amount of land burned by fires has decreased globally over the past two decades, carbon emissions from fires have not declined. Our study shows that this mismatch is largely due to savanna fires becoming more intense, releasing more carbon per unit area burned. We used statistical and machine learning tools to uncover the key causes of this intensification, including increasing fuel loads and shifts in climate conditions such as rainfall, soil moisture, and wind. These findings highlight the critical role of savannas in shaping global fire emissions and underscore the importance of considering both ecological and climate factors in fire management and climate policy.