Guest column: Wildland fire causes complicated

Do you believe today’s wildfires are mostly caused by climate change? It’s far more complicated, writes John Snyder.

In a recent column I questioned the claim that increased wildfire numbers and acres burned in California in 2017 are due to human-caused global warming. Despite increasing atmospheric CO2 concentrations over the past 40 years, the number of wildfires in California has decreased according to California fire statistics.

However, if one searches on “cause of western wildfires,” a very different story is presented in the popular press, namely that climate change caused by humans is responsible, and that it’s going to get worse. For example, the Mother Jones website (Oct. 11, 2017) states “Here’s Why Wildfires Will Only Get Much, Much Worse” and The Atlantic Magazine website (July 7, 2017) asks “Has Climate Change Intensified 2017’s Western Wildfires?”

Both reports refer to a “study” reported in a scientific publication last year, which claims that more than half of the increase in forest acreage burned in the last 33 years is due to human-caused climate change.

However, both stories are misleading because they imply that all wildland fires are the same. They are not. They differ based on fuel source, ignition, location, climate and time of year. Each factor includes multiple variables.

Each story includes a full-frame, fiery image of a wildland fire near populated regions of California. Each story references the devastation of the wildland fires this year. Each story then refers directly or indirectly to the study that attributes over half of the increase in forest-fire area burned between 1979 and 2015 to human-caused climate change.

The Atlantic story states: “And global warming is already having an effect on wildfire. In a paper published last year… [the researchers] found that the total area burned in the western United States over the past 33 years was double the size it would have been without any human-caused warming.”

The problem with this statement is that the researchers are talking specifically about fires that burned forest land. They did not study wildland fires, like the one shown in the image, that burned much of California this year. In this case the difference is critical. As just one example, summer drought correlates with forest fires and previous winter precipitation correlates with fires in shrub and grassland ecosystems.

As for Mother Jones: “And … [the] study, released last year, concluded that human-caused climate change is responsible for doubling the amount of land burned in the American west since 1984.” This statement is false, period. Again, the study was limited to forest fires, not to wildland fires in general. The Mother Jones’ implication that wildfires will only get worse due to human-caused global warming is not supported by the reporter’s story, nor the study.

Understanding how and why wildland fires occur is complicated. Letters to the editor and popular press stories which lead the reader to assume that human-caused global warming is responsible for wildland fires are background noise that should be met with a healthy dose of skepticism.

There is a tremendous body of excellent research that examines the relationship between climate and wildland fires. One example is “Different historical fire-climate patterns in California:” See: The problem is that this type of study doesn’t generate the convenient sound-bites used by the popular press.

In a follow-up column, I’ll take a closer look at the uncertainties underpinning the conclusions of the study.

Snyder is retired commercialization manager of Idaho National Laboratory.