This archive report was first published on 28 October 2019.
California's recent wildfire disasters have left many wondering about the root causes. While poor maintenance by utilities like PG&E, expanded human settlement at the margins of fire-prone woodlands, and global warming are all contributing factors, they do not fully explain the suddenness and persistence of the change experienced in the last three years.
Research by Park Williams, an expert on wildfire and climate, shows that the area burned by fires each year in the summer months has increased drastically, consistent with the influence expected from global warming. However, Dr. Williams' research also suggests that the headline-making fires of the last three years have all occurred in fall, where temperature plays a role, but other factors like the dry Diablo and Santa Ana winds are more important.
These winds, mainly fall and winter phenomena, are critical factors in the recent and current fires. However, they are projected to occur less frequently as the climate warms, with no clear trend yet apparent in the observations. This raises questions about the role of human activity in the fires.
So, what is going on? One possible explanation is that the sparking might have gotten worse over time, but more importantly, it has encountered the hot, dry downslope winds markedly more often. Global warming may be making those winds a little hotter, but the wind events themselves may be inherently unpredictable, making them a matter of bad luck.
Alternatively, the causes of the fires may be in principle knowable, but current science just doesn't know them. Climate change may be proceeding more rapidly and dangerously than we understand, but it's essential to understand the limits of our knowledge to keep us humble about our place on the earth.
