In Climate Accounting, Fire’s an Orphan

The frenzied 2002 wildfire season on the front range of the Rocky Mountains southwest of Denver got an early and intense start. On an April afternoon, teenagers sneaking a cigarette in the woods behind Platte Canyon High School on the edge of the town of Bailey inadvertently set off the first big one, a conflagration that would sweep across 2,600 acres.

That had Chris Hendrick and his wife, Beatrice, scrambling. Chris, a Spanish teacher and coach at the high school, wound up rushing back toward home from an afternoon track meet at another school after he got word of the fire, which at first had seemed tamed but was spreading fast.  

Beatrice, meanwhile, found herself loading their two small children and a couple of other kids she was looking after into their minivan after smoke began to billow menacingly over a ridge near their home a few miles from town.   

Their house was never actually threatened, but in what Chris called “a really scary year,” fires kept coming “one after another after another. We were waking up almost every morning to the smell of smoke.”

The June Hayman Fire, only about five miles east of Bailey, was the worst of that terrible season—in fact, the worst wildfire in Colorado’s recorded history. Propelled by dry winds, it raced across 60,000 acres on a single day, in the end scorching 138,000 acres across four counties. Although much of the burned landscape was within the Pike National Forest, the fire destroyed 133 homes on surrounding forested private land and forced more than 5,000 people to evacuate.

“Fire is as elemental as air or water. We live on a fire planet. We are a fire species.”
Jennifer Balch

In the summer of 2008, I drove with Hendrick down a steep winding road through a section of the Hayman Fire landscape. Firefighters had managed to save several dream homes scattered on the slopes here, but the dream views were gone. The houses sat incongruously and eerily intact in a ghost forest of charred and blackened trunks and broken-off boles.

It was a firsthand look at one of the consequences of two decades of drought in the American West, but also at a consequence of the all-too-human desire to live in wild and beautiful natural landscapes, including landscapes whose nature it is to burn from time to time. One could, more or less, mark the beginning of two decades of drought with the fires that raged through about two-thirds of Yellowstone National Park in 1988. And one couldn’t fail to notice the most recent manifestation of the paradox of that human desire to live in the midst of combustible fuel with August’s headlines about the 20-mile wall of flame that devoured entire swaths of suburban and exurban Los Angeles. These are not merely phenomena of the United States: Last summer also offered up media images of big fires glowing in suburban zones within sight of Athens’ Parthenon, a reprise of a horrific 2007 fire season in Greece. And early in 2009, in the intense heat of a down-under summer, parcels of Australia’s Victoria state went violently ablaze, trapping and killing scores. 

Wildfire, of course, has been part of life on Earth’s vegetated lands since there were vegetated lands or, at least, vegetation dry enough to ignite in the presence of abundant oxygen and a source of ignition: lightning or volcanic ember. But there do appear to be new factors at play. The world’s tropical rainforests are being set ablaze to clear land for agriculture. In both tropical and temperate zones, the world appears to be experiencing more large, uncontrolled fires. In some areas where fires haven’t yet burned, entire landscapes have been unwittingly manipulated into hyperflammable disasters-in-waiting. Fire, meanwhile, is interacting with a changing global climate in ways that are, as yet, poorly understood and inadequately accounted for by existing science, even though those interactions include snowballing “feedback effects,” whereby warmer climate begets more drought, begets more fire, begets more carbon emissions, begets more warming.

Those are some of the key conclusions of a remarkable article titled “Fire in the Earth System,” which appeared in April in the journal Science. Authored by 22 experts in fire science from six nations, the piece is a sweeping, if condensed, overview of what the scientific world knows, and doesn’t know, about fire on Earth.

David Bowman, a fire ecologist at the University of Tasmania and one of the paper’s two lead authors, says the work is the first of its kind. It came about after scholars who study various aspects of fire got together at a two-week conference in 2008 to try to put the subject into what Bowman calls “some kind of unified synthetic framework.” Previously, he says, fire had been studied piecemeal from an array of perspectives—fire management, fire ecology, pollution epidemiology—“but the whole has never been seen.”

The paper’s other lead author, Jennifer Balch, Ph.D. ’08, began her own research on fire in the Amazon rainforests while still a doctoral candidate at F&ES. Now a postdoctoral fellow at the National Center for Ecological Analysis and Synthesis at the University of California, Santa Barbara, which helped host the conference, Balch sums up the epiphany that came as the expert participants began to compare notes.

“You could almost see the light bulbs starting to go off,” she said. “We began to see what a huge player fire has been on the Earth, a much bigger player than anyone really appreciated.”

One key conclusion of the Science article got some news media attention: that the deforestation fires set to clear land, today principally in the tropics, are contributing far more to climate change than accounted for in projections by the Intergovernmental Panel on Climate Change. According to an estimate the authors admit is preliminary, these fires alone have accounted for nearly one-fifth of human-caused global warming to date.        

But the study is even more far-reaching. It looks at factors ranging from human evolution and history in relation to fire to the reasons why recent fires are often larger and more destructive. In the end, the article calls not only for more attention to the role wildfire plays in climate change, but also for a far more integrated scientific approach to what the conference dubbed “pyrogeography,” the study of the myriad aspects of fire on Earth.     

Balch sums up the big picture this way: “Fire is as elemental as air or water. We live on a fire planet. We are a fire species.”

We live on Balch’s “fire planet” because, she explains, the Earth and its living systems have been interacting with fire for about 400 million years. Fire has affected planetary and ecosystem factors that range from levels of oxygen and carbon dioxide in the atmosphere to the cycling of the nutrient phosphorus.

Fire ecologists have documented how some species have evolved in the presence of recurring fires. Near the top of the mitt-shaped lower peninsula of Michigan, for instance, the now-endangered Kirtland’s warbler, sometimes dubbed the “bird of fire,” successfully nests under low-lying boughs only in forests of recently burned, but regenerating, jack pine—trees that can regenerate only after the intense heat of the frequent fires pries open their cones for seed release. 

We, too, are a “fire species,” in Balch’s view, because our own evolution has been intertwined with fire. It appears that it was recurring fire that suppressed the growth of trees on the world’s savannas. It was on the African savanna, in the presence of abundant and accessible game, that humans evolved. Over time, humans learned how to use fire to their own ends, for cooking, warmth, signaling and, eventually, for more dramatic ends, the management of the lands around them.

The Science article points to evidence that humans evolved with some tolerance to smoke. Tolerance appears to be greatest among those who descended from colder-climate ancestors, whose domestic fires burned in more confined spaces. And then there’s the matter of making some space for the very grey matter that defines our species. According to Balch, evidence suggests that when hominids learned to cook, and thereby tenderize food, it allowed the evolution of a smaller jaw, which in turn may have allowed the skull to accommodate a larger brain.

Sometime in the span of tens of millions of years ago, humans began to use fire to control fuel loads and to manage landscapes. For example, long before European colonization, Native Americans periodically set fire to clear land for such purposes as managing hunting grounds for game species, including deer, which tend to thrive in clearings, forest edges or young, early successional forests. Fire abounded as European settlers arrived, then marched westward, clearing forests as they moved.

In the past two decades, satellite imagery has offered a detailed picture of contemporary life on our “fire planet.” Notably, it has shown us that fires, sometimes of tens of thousands of acres, are burning in rainforests, in what Balch terms “a pantropical band of fire.”

“In some ways, what’s happening in the tropics today isn’t that different from what happened in North America after colonization. But it’s happening at breathtaking speed,” she says.

In other ways, though, the tropical fires are something new—the Earth’s wet forests are burning. “The idea of frequent large-scale fires in the tropical rainforest used to be unthinkable,” says Balch, “Now we’re seeing several large fires every decade.”

In both tropical and temperate zones, climate change appears to be playing a role. In the American West, larger and more intense fires dovetail with measurable increases in temperatures and earlier snowmelts.

But there’s at least one additional major factor—the unintended consequences of years of fire suppression in forests that evolved in the presence of periodic fires, a phenomenon Bowman calls “Smokey the Bear blowback.” 

Fire suppression can lead not only to a buildup of fuel in a forest, but to dramatic changes in forest structure. Recurring, cooler fires might once have been restricted to periodically burning off and suppressing the growth of low-lying vegetation. Today, with these natural fire patterns themselves suppressed, taller undergrowth becomes not only fuel for hotter fires, but functional ladders that allow flames to leap into canopies, killing mature trees that would have easily survived the lower, cooler fires.

Fire, meanwhile, is interacting with climate in a complex, and still poorly understood, dance. A forest fire releases carbon dioxide into the atmosphere, but a regenerating forest can take the carbon back up. But if a farm field replaces the forest, the carbon uptake calculus changes. Fires can also alter surface reflectance (or albedo). A scorched, blackened landscape absorbs rather than reflects heat. A young, greened-up landscape that shortly follows a burn might reflect more heat than the original forest.

To arrive at their rough estimate of the sort of influence that fire could be having on climate, the paper’s authors focused solely on intentionally set deforestation fires. They estimated that these fires have been responsible for 19 percent of the human-caused global warming to date. That’s a piece of the equation, the author’s contend, that’s missing from existing climate models.

“We’re arguing,” says Balch, “that a new generation of climate models needs to do a much better job of accounting for fire.”

In a more sweeping sense, the 2008 conference and the 2009 article that followed might signal a coming day when science does a much better job of integrating the study of fire on Earth. Whether “pyrogeography” becomes a formal new discipline is an open question. But perhaps it is at least an early hint that the study of fire may no longer be what Bowman calls “an intellectual orphan.” 

As he puts it, “How could something be so obvious and yet be so long overlooked?”

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