Wildfires and Statistical Deception
Fox News reminds me of the schizophrenic guy who lives on my block. I can't always predict what he'll say, but I'm fairly sure some of it will be crazy, or at least wrong.
I want to talk about a statistical deception I noticed in a Fox News article this week. This interested me, because the stats are inaccurate, and because even if you assumed they were correct, the writer used one of the oldest tricks in the book to squeeze a false conclusion out of them.
The Fox News article
The purpose of this article was to criticize the U.S. Department of Defense for publishing a report four months before the Russian invasion of Ukraine that focused on climate change but failed to mention either country. The author was incensed by this oversight, because he believes that climate change isn't real.
The main content of the article consists of "evidence" that environmental conditions routinely linked to climate change are actually improving rather than getting worse. (I'm serious.)
Foxnews.com is the 5th most frequently visited newsite in the U.S., so when I see an article like this on its home page, I get concerned. The writer, Chuck DeVore, is not some schizophrenic guy who lives up the street. He's a vice president at the Texas Public Policy Foundation and, to be frank, he seems deeply misguided at best.
Some wildfire statistics
My focus will be one of the many statements Mr. DeVore made in hopes of "proving" that climate change is not real, or at least not damaging:
"Wildfires used to burn about 4.2 percent of the land annually in the early 1900s; now, it’s 2.5 percent."
In other words, climate change couldn't be exacerbating our wildfire problem, because the problem has diminished during the time when climate change was supposedly becoming more severe.
Are the statistics accurate?
In the sentence I quoted, the writer seemed to be referring to wildfires in the U.S., but whether his stats were intended to be national or international, I've been unable to corroborate them.
Let's assume anyway that he was in the ballpark, because experts do agree that since the late 1800s, the frequency and severity of wildfires has declined. Even if those declines continued through the present (which they don't, as I'll explain later), it wouldn't follow that climate change isn't the main cause of our increasingly horrific wildfires. (I'll explain that later too.)
A mini-history of wildfires
Experts agree that for thousands of years, the main predictor of the frequency and severity of wildfires is climate – more fires when it's hotter and drier, fewer fires when it's cooler and wetter. These trends have been corroborated through studies on sedimentary charcoal, fire scars, historical records, etc. (Scientific findings are much more persuasive when different methods converge on the same conclusions.)
In recent centuries, anthropogenic (i.e., human) factors have increased wildfire activity, through our impact on climate change, as well as in more direct ways. In the U.S., the peak came during the second half of the 19th century. Settlers caused fires, both deliberate and accidental, in the process of clearing forests and brush, driving game, etc. Locomotives caused fires, through sparks emitted from smokestacks and brakepads. The mere expansion of people caused fires, because, well, we screw up sometimes, and occasionally even commit arson.
In the 20th century wildfires began to decline. At first, widespread grazing of domesticated cattle reduced the amount of flammable vegetation, and new laws required railroad companies to clear vegetation away from tracks and to install spark arresters. Changes like these, along with a shift from wood to coal, reduced the extensive number of wildfires caused by locomotives. That's not the end of the story though. Increasing numbers of trails and roads limited the spread of wildfires. Logging and prior burns increased the numbers of trees (particularly young stands and aspen stands) that are relatively resistant to burning. And, importantly, in the second half of the 20th century we got much, much better at suppressing fires. This brings us to the mid-1980s.
What's happened most recently?
Among other things, climate change in recent decades has led to warmer conditions, drier conditions, and longer annual durations of both, all of which have increased the incidence and severity of wildfires.
Although the exact statistics vary from source to source, here's what's happened since the 1980s:
—the average wildfire season is about three months longer
—the number of large wildfires per year in western states has roughly tripled
—the amount of acreage burned has roughly doubled
These statistics aren't completely inconsistent with the pattern implied by the Fox News writer. It's true that wildfires have declined since the turn of the 20th century. But they would've declined even more if not for climate change. And, there's that sharp uptick since the 1980s. With respect to acreage burned, the historical changes look much like a u-shaped curve:
In other words, the amount of acreage burned in recent years is reaching and beginning to exceed that observed at the outset of the 20th century. (The actual u-shaped curve would have a more jagged look, as there's variation from year to year along with the general trend I've depicted. I’m avoiding details here because experts agree on this u-shaped trend but not on the specific stats.)
The statistical trick
Let's assume that the Fox News stats had been perfectly accurate, and that wildfire severity had indeed declined over the past century. This still wouldn't rule out climate change as a major contributor to recent wildfires.
To illustrate, suppose you go on a diet and, after a year, you notice that you’ve lost 12 pounds. Suppose too that during the year you ate an enormous chocolate sundae before bed every night. The fact that you lost 12 pounds would show that you made lots of changes during the year (exercising more, eating smaller and more healthy meals, etc.) that caused you to lose weight. However, it wouldn't show that eating an enormous sundae before bed contributes to weight loss. After all, if you'd replaced each sundae with a slice of watermelon, you might've lost even more weight.
The "trick" that the Fox News writer played was to imply, falsely, that every contributor to a statistical trend must be consistent with that trend. His logic was this: If we assume that climate change makes wildfires worse, then a decline in wildfires would mean that climate change isn't occuring. According to this logic, the fact that you lost 12 pounds means that it's impossible that eating those sundaes could've caused any weight gain.
In fact, not all contributors to an overall trend need to reflect that trend. Eating enormous sundaes every night causes weight gain, even if the gain can be offset by other factors. Likewise, climate change can exacerbate a wildfire problem, even if other factors reduce wildfire activity.
Postscript
I don't mean to imply that it's only Fox News, or conservatives more generally, who play the trick I described in the previous section. I imagine that at least once during the 2022 mid-terms, I'll be calling out both parties for making use of this trick. In the meantime, although I do try to be nonpartisan in these newsletters – I did point out a mistake in the New York Times last week – I admit to falling short of this ideal at times.
Q: Why did the Fox News christmas tree catch fire?
A: They left it too close to the gaslight.
Appendix: Statistical error inertia
Fox News isn't the first conservative source to misrepresent wildfire stats. For example, last year the Heartland Institute published an article claiming that "U.S. acres burned each year are much fewer now even in our worst years than was the case in the early 20th century." Politifact, an independent fact-checking organization, has done an excellent job of dissecting and refuting this claim. What happened is a combination of mistakes on the part of a federal agency, combined with conservatives' unwillingness to acknowledge that the agency has since addressed those mistakes.
Here's the story: For years, the National Intragency Fire Center maintained publicly available wildfire data on its website that the NIFC knew to be inaccurate. Specifically, wildfire data reported to the NIFC in the early 20th century was unreliable because each federal, state, and local agency that provided these data used its own methods of calculation and often didn't coordinate with each other. As a result, some wildfires were counted twice or three times in the NIFC database. Another problem is that the individual agencies often reported any sort of fire, regardless of whether it was a wildfire or prescribed (i.e., one that's deliberately set and controlled, under government authority). On the whole, these and other methodological problems resulted in overestimates of the extent of early 20th century wildfires. The NIFC didn't make a correction to their website until recently. Meanwhile, the scientific consensus is that wildfires in the early 21st century have reached and are now exceeding early 20th century levels. And, in the end, the strongest statistical predictor of wildfires continues to be climate. Climate change is real, and record-breaking wildfire seasons over the past few years are among the consequences.
For those of you planning outdoor trips this spring and summer, here are some tips for preventing wildfires.