As one wildfire expert wrote, “Predicting future fire regimes is not rocket science; it is far more complicated than that.”
But regardless of accuracy, most people are attracted to very simple narratives such as: more CO2 causes global warming causes more fires. Accordingly in the summer of 2019, CNN trumpeted the headline California wildfires burn 500% more land because of climate change. They claimed, “the cause of the increase is simple. Hotter temperatures cause drier land, which causes a parched atmosphere.” CNN based their claims on a scientific paper by lead authors Park Williams and John Abatzoglou titled Observed Impacts of Anthropogenic Climate Change on Wildfire in California. The authors are very knowledgeable but appear to have hitched their fame and fortune to pushing a very simple claim that climate change drives bigger wildfires. As will be seen, their advocacy appears to have caused them to stray from objective scientific analyses.
If Williams and Abatzoglou were not so focused on forcing a global warming connection, they would have at least raised the question, ‘why did much bigger fires happen during cooler decades?’ The 1825 New Brunswick fire burned 3,000,000 acres. In Idaho and Montana the Great Fire of 1910 burnt another 3,000,000 acres. In 1871, the Great Michigan Fire burned 2,500,000 acres. Those fires were not only 6 times larger than California’s biggest fire, they occurred in moister regions, regions that don’t experience California’s Mediterranean climate with its guaranteed months of drought each and every summer. If those huge devastating fires occurred in much cooler times, what are the other driving factors of big wildfires?
Bad analyses cause bad remedies, and here is why Williams and Abatzoglou’s last paper exemplifies a bad scientific analysis. Analyzing changes in California’s burned areas from 1972 to 2018 they claimed, “The clearest link between California wildfires and anthropogenic climate change thus far, has been via warming-driven increases in atmospheric aridity, which works to dry fuels and promote summer forest fire.” But natural cycles of low rainfall due to La Niñas also cause dry fuels. The increase in burned area is also attributed to increases in human ignitions such as faulty electrical grids, to increased surface fuels from years of fire suppression, and to changes in vegetation that increased the abundance of easily ignited fine fuels like annual grasses. Furthermore, temperatures in some local regions experiencing the biggest fires have not been warming over the past 50 years (See temperature graphs in this essay’s last segment. Data from Western Regional Climate Center). All those factors promote rapid wildfire spread and greater burned areas. Although good science demands separating those contributing factors before analyzing a possible correlation between temperature and area burned, Williams and Abatzoglou oddly did not do so! That’s bad science.
Although Williams and Abatzoglou did acknowledge that other factors modulate the effects of warming on burned areas they admitted their statistical correlations did not “control” for those effects. To “control” for all those contributing factors, they could have easily subtracted estimates of burned areas associated with those factors. For example, a 2018 research paper estimates, “Since the year 2000 there’ve been a half-million acres burned due to powerline-ignited fires, which is five times more than we saw in the previous 20 years.” Did Williams and Abatzoglou not do the needed subtractions of other well-established factors because it would weaken their global warming correlation?
Similarly, CNN journalists were content to simply blame climate change. However, in light of the increasing devastation caused by powerline-ignited fires, good investigative journalists should have asked the former California Governor Jerry Brown if he now regrets having vetoed the bipartisan bill crafted to secure the power grid; an action that could have saved so many lives and property. Instead CNN simply promoted Brown’s persistent climate fearmongering quoting, “This is only a taste of the horror and terror that will occur in decades.”
Ignoring the complex effects of human ignitions, CNN also parroted claims that global warming is causing fire season to last all year. But as seen in the graph below from a 2017 wildfire study, the United States’ natural fire season is due to lightning and only dominates during the months of July and August, when California’s high wind events are low. In contrast it is human ignitions that extend fire season, dramatically increasing ignitions throughout the winter months when fuel moisture is higher, and into seasons when cooling desert air generates strong episodes of Santa Ana and Diablo winds. Those high winds cause fires to spread rapidly, burning 2-3 times more area than fires ignited during low winds, and California’s most destructive fires recently occurred during those high wind events. However, like other researchers, Williams and Abatzoglou reported no trend in those destructive California winds. Furthermore, climate models suggest a warming climate should cause weaker winds. So, without a change in California’s windy conditions, high winds can’t be blamed, directly, for the increased burned areas. However, because more human-caused ignitions occur during the winter, it increases the probability that more fires will be amplified by those strong winter winds. As US Geological Survey’s wildfire expert states, “Some will argue that it’s climate change but there is no evidence that it is. It’s the fact that somebody ignites a fire during an extreme [wind] event.”
The timing of human ignitions is but one driver of more and bigger fires. Increased surface fuels are another huge factor.