This article contains an addition.
Longer and more intense fire seasons in the western United States are one of the most visible manifestations of climate change’s impact in the region. And the role that global warming plays in fire regimes—and the corresponding effects that fire has on climate change by releasing the carbon dioxide stored in vegetation into the atmosphere—is getting increased research attention.
From the 1960s through the end of the 20th century, wildland fires claimed about 3.5 million acres per year in the United States, according to the National Interagency Fire Center, or NIFC, in Boise, ID. Only once in that 40-year period did forest and grass fires burn in excess of 7 million acres.
But since 2000, there has been a dramatic spike, not just in the acreage burned—more than 7 million acres every year on average—but in the size of wildland fires and their duration. In 2002 alone, Colorado, Arizona, and Oregon had huge fires that set modern records, with the Hayman, Rodeo-Chediski, and Biscuit fires burning 138,000, 467,000, and nearly 500,000 acres, respectively.
As a result, more researchers are taking a closer look at the effect of these fires on climate. A new paper in the April 24 issue of the journal Science, for example, concludes that scientists have greatly underestimated the impact that deforestation brought on by fires has on climate change. On a global scale, fires release into the atmosphere about half of the carbon dioxide that is contributed by the use of fossil fuels.
“It’s very clear that fire is a primary catalyst of global climate change,” co-author Thomas W. Swetnam told ScienceDaily. “Fires are obviously one of the major responses to climate change, but fires are not only a response—they feed back to warming, which feeds more fires… The scary bit is that, because of the feedbacks and other uncertainties, we could be way underestimating the role of fire in driving future climate change.”
Swetnam and the report’s 21 other authors urged the Intergovernmental Panel on Climate Change to pay more heed to the role of fire in developing future climate change models.
In the United States, the 2009 fire season is already underway, with large and destructive fires recently hitting Oklahoma, Texas, and South Carolina. In coming weeks, fire season will arrive across the Rocky Mountain West, moving south to north as spring turns to summer.
NIFC’s wildland fire outlook issued May 1 predicts above normal fire potential in the southwest from Texas to Arizona, Washington State, and California. Fire potential is predicted in the normal range for the rest of the West.
How destructive this fire year will turn out to be is impossible to predict with any real accuracy, but the trend of larger fires, huge acreage burned, and longer fire seasons is likely to continue as global climate change affects the West.
Higher temperatures associated with climate change began to have what would become a profound impact on wildland fires in the West in the mid-1980s, according to a 2006 study published in Science by four researchers who studied 1,166 fires of more than about 1,000 acres between 1970 and 2003.
From 1986 onward, the researchers found, “wildfire frequency was nearly four times the average of 1970 to 1986, and the total area burned by these fires was more than six and a half times its previous level.” Further, the length of the wildfire season increased by 78 days.
The timing of spring snowmelt was a critical factor, according to the study, with most fires and most acreage burned during years when snow melted early in the year and soils and vegetation dried more. Those findings do not offer a happy prospect for the West, where most research predicts that climate change will melt mountain snowpacks earlier.
And because of the importance of western forests in sequestering carbon, the impacts of longer and more intense fire season won’t be felt just in the West.
“Current estimates indicate that western U.S. forests are responsible for 20 to 40 percent of total U.S. carbon sequestration,” the researchers in the 2006 study wrote. “If wildfire trends continue… this biomass burning will result in carbon release, suggesting that the forests of the western United States may become a source of increased atmospheric carbon dioxide rather than a sink, even under a relatively modest temperature-increase scenario.”
The rapid growth in the size and intensity of wildland fires also serves as another good example of the huge financial costs of failing to curb global warming.*
Federal government expenditures to prepare for and fight fires nearly tripled from $1.1 billion per year in the fiscal 1996 to fiscal 2000 period to $2.9 billion per year in the five years that followed, according to a 2007 Governmental Accountability Office report. Actual firefighting costs on average during those two periods nearly quadrupled from $522 million to $2.1 billion.
The 2006 study is a strong argument for both a global attack on climate change and the West’s push toward an energy mix that relies far more on renewable sources of power and less on fossil fuels. Restoration of the region’s dry, mid-elevation forests that have become overcrowded and ripe for large, catastrophic fires after decades of fire suppression can also play a positive role. Under natural conditions those forests typically had frequent, low-intensity fires that cleaned out underbrush and small trees.
But the researchers in the 2006 study found that the bulk of increased fire activity in the West came in Northern Rockies forests that naturally have infrequent large fires and are less affected by the kind of poor land management and fire exclusion seen in the central and southern Rockies.
“[T]he broad-scale increase in wildfire frequency across the western United States has been driven primarily by sensitivity of fire regimes to recent changes in climate over a relatively large area,” the researchers wrote. As a result, they concluded, “ecological restoration and fuels management alone will not be sufficient to reverse current wildfire trends.”
* Addition, May 8, 2009: Information added on federal expenditures for firefighting.