A call to refine fire attribution: expanding the FAR statistic to capture the complexity of Los Angeles extreme fires

The January 2025 wildfires in Los Angeles resulted in a tragic loss of life and major damage to homes, infrastructure, and public health. Two key questions are: to what extent did climate change increase the likelihood of the event, and what role did direct human actions play? Direct human actions could encompass expanding urban developments into wildlands, unattended campfires, sparks from faulty equipment such as powerlines, or deliberate changes to land cover that may slow wildfire spread. Attribution studies generally address the first climate-related question by using the Fraction of Attributable Risk (FAR), a metric based on changes in meteorological conditions. However, this approach can oversimplify the complex drivers of fire, especially in regions like Los Angeles, where topography, vegetation, and ignition sources interact with large-scale climate signals. This suggests a need to extend FAR statistics to incorporate these factors and to translate them into more meaningful quantities such as fire emissions, health and air quality impacts, and economic losses. We use “FAR” as a general term throughout to refer to either that specific statistic or its derivatives, such as risk ratio or probability ratio.