Posted by Curt on 10 November, 2019 at 7:53 am. 5 comments already!


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 CaliforniaThe 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. It is well known that past fire suppression has allowed surface fuels to accumulate in forests, leading to bigger and more devastating fires. But the changes in surface fuels are more complex. Some scientists point out that certain logging practices spread “invasive grasses called cheat grass, for example, and other ones that form this really thick mat across the area after logging and that grass just spreads flames very rapidly and fires burn very intensely through that.” California’s Democrat congressman Ro Khanna has been arguing that the U.S. Forest Service policy to clear cut after a wildfire is making California’s forest fires spread faster and burn hotter by increasing the forest floor’s flammable debris. Khanna says, “Because we don’t have the right science, it is costing us lives, and that is the urgency of getting this right.”

Controlling the spread of cheat grass is urgently needed. Grasses are “fine fuels” that ignite most easily. The 2018 Carr Fire was California’s 7th largest fire and threatened the town of Redding, California. It started when a towed trailer blew a tire causing its wheel rim to scrape the asphalt creating a spark which ignited roadside grasses. Those grasses carried the fire into the shrublands and forests. Grasses are classified as 1-hour fine fuels, meaning they become highly flammable in just one hour of warm dry conditions. Climate change is totally irrelevant. It does not matter if it was wet and cool, or hot and dry during previous days, weeks or years. Just one hour of warm dry fire weather sets the stage for an explosive grass fire that then gets carried into the forests. Fire weather happens every year, and partially explains why fires could burn 3,000,000 acres in the cool 1800s.

It was not human ignition but lightning that caused the 2012 Rush Fire. It was California’s 4th largest fire burning 272,000 acres of sagebrush habitat, which then continued to burn additional area in Nevada. Historically, because surface fuels are scarce, hot dry sagebrush habitat rarely burned (once every 60-100 years). But invasions of non-native cheat grass have now provided ample fuel to turn small lighting fires into huge conflagrations. Eleven of the USA’s 50 biggest fires in last 20 years are in the Great Basin, where invasive cheatgrass is spreading. Nevada’s largest fire was the 2018 Martin Fire. Rapidly spreading through the cheat grass, it burned 439,000 acres. Cheat grass fires are a great concern for biologists trying to protect the threatened Sage Grouse as cheat grass-dominated sagebrush habitat now burns every 3-5 years. Habitat with high cheat grass abundance are “twice as likely to burn as those with low abundance, and four times more likely to burn multiple times between 2000-2015.”

When experts estimate impending fire danger, they determine how fast a fire will spread. The Spread Component considers the effects of wind and slope and daily changes in the moisture content of the surface fuels. Large dead trees may become flammable after 1000 hours of warm dry conditions, but still thick fuels only ignite if fast burning surface fuels supply enough heat. Thus, the Spread Component only considers smaller-diameter fuels like grasses that can dry out in an hour, as well as twigs and small branches that dry out within 10 to 100 hours. Central and Southern California are dominated by shrubby habitat with small diameter fuels that allow fire to spread rapidly. The December 2017 Thomas Fire was California’s 2nd largest fire. Its human ignition coincided with a Santa Ana wind event resulting in the burning of 282,000 acres in southern California.

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