Wildfires have been attributed more and more to climate change, but it’s really not that simple, writes John R. Snyder, Ph.D.
Last year’s media frenzy over climate change and California wildfires shows why our schools need to teach critical thinking skills and to question conventional wisdom, whether it’s science-based or not.
An earlier Commentary letter claimed that CO2 emissions from burning fossil fuels causes global warming, which then caused the widespread and destructive California wildfires in 2017. However, it’s not that simple.
While atmospheric warming may contribute to localized drought, and drought is a factor in the number of wildfires and the acres burned, it is important to remember that drought is only one factor; there are many other causes of wildfires, both natural and man made.
But let’s examine the relationship between atmospheric CO2 concentrations and the 2017 California wildfires. CO2 concentrations prior to 1958 were less than 320 parts per million. Since 1958, CO2 concentrations have increased consistently and dramatically to over 400 ppm today.
If we accept that atmospheric CO2 concentration is the cause – or even a major cause – of the number and destruction of wildfires, then historical records for CO2 and wildfires should be directly proportional. That means the number and destructiveness of wildfires should have steadily increased since 1958.
Instead we find that the number of wildfires in California has steadily “decreased” for nearly 40 years; from 9,009 in 1980 to a low of 2,434 in 2010 (CAL FIRE statistics). In contrast, preliminary reports for 2017 are 7,117 wildfires. The decrease in wildfire numbers were described in the International Journal of Wildland Fire (April 2017): “Different historical fire-climate patterns in California.”
While the number of wildfires has steadily decreased, the acres burned has shown a positive trend. However, an author expresses caution in ascribing the increase to global warming: “People who have written on it tend to ascribe it to climate change, but I think we are a long way from knowing if that is what is going on.”
According to the author, “One reason acreage [burned] may be up is from the record winter rains that replenished fuel by spawning plant growth, including the return of grass that has disappeared from wildland areas throughout Southern California during the drought.”
Any hypothesis that CO2 causes an increase in wildfire numbers and destruction must explain the 40-year trend of declining California wildfire numbers despite increasing CO2 concentrations.
So why have the number of California wildfires decreased since 1980? According to one study, “there is now a forest “fire deficit” in the western United States…” attributable to human activities (e.g., fire suppression, grazing), ecological and climate changes. The study was summarized by Wildfire Today, which concluded “We owe the ecosystem some fire, and the debt collector has come to visit.” Records for the last 1,500 years suggest that the number of western wildfires should be increasing, not decreasing as they have in California since 1980; therefore, a fire deficit. The 2017 California wildfire impact was similar to the peaks observed in the geological record and in the 1800’s.
A Google search on “cause of western wildfires” brings up several links relevant to this discussion. One is on the Mother Jones website which reinforces the human-caused climate change argument. Another is FactCheck.org., which says, “The answer is: It’s complicated.”
Snyder is retired commercialization manager of Idaho National Laboratory.