Heating Up

One of the many extreme weather effects of global warming, wildfires now occur more frequently, burn longer, and burn hotter than ever before.

Forest fire

The changing global climate isn’t the only thing affecting wildfires; bark beetles, which infest and kill forests, have taken to the warmer weather and increased the risk of fires.

Photo by Fotolia/gilitukha

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Carbon dioxide in the air is a great cause of climate change, making springs warmer, droughts longer, and winter snow melt more rapidly. What you may not realize is that these factors create longer burning seasons for wildfires, which, as they burn longer and hotter, emit more CO2 so that the cycle repeats. And it’s not only wildfires that have increased in frequency. The last decade has seen superstorms, forest fires, heat waves, and droughts, to the point where the affects of climate change have been impossible to ignore. Joseph Romm has written an up-to-date, comprehensive examination of the science behind climate change, what these environmental issues mean for the future, and possible clean energy solutions. Climate Change: What Everyone Needs to Know

is a presentation of how the changing environment will impact nations, families, and you.

How Does Climate Change Affect Wildfires?

Global warming makes wildfires more likely and more destructive—as many scientific studies have concluded. Why? Global warming leads to more intense droughts, hot­ter weather, and earlier snowmelt (hence less water available for late summer and early autumn). That means wildfires are a dangerous amplifying feedback, whereby global warming causes more wildfires, which release carbon dioxide, thereby accelerating global warming.

Back in 2006, the journal Science published “Warming and Earlier Spring Increase Western U.S. Forest Wildfire Activity,” which analyzed whether the recent soaring wildfire trend was due to a change in forest management practices or to climate change. The study, led by the Scripps Institute of Oceanography, concluded it was climate change:

"Robust statistical associations between wildfire and hydroclimate in western forests indicate that increased wildfire activity over recent decades reflects sub- regional responses to changes in climate. Historical wildfire observations exhibit an abrupt transition in the mid-1980s from a regime of infrequent large wild­fires of short (average of 1 week) duration to one with much more frequent and longer burning (5 weeks) fires. This transition was marked by a shift toward unusually warm springs, longer summer dry seasons, drier veg­etation (which provoked more and longer burning large wildfires), and longer fire seasons. Reduced winter pre­cipitation and an early spring snowmelt played a role in this shift."

That 2006 study noted global warming (from human-caused emissions of greenhouse gases such as carbon dioxide) will further accelerate all of these trends during this century. The 2007 review and assessment of the scientific literature by the Intergovernmental Panel on Climate Change acknowledged the danger:

"A warming climate encourages wildfires through a longer summer period that dries fuels, promoting eas­ier ignition and faster spread. Westerling et al. (2006) found that, in the last three decades, the wildfire season in the western U.S. has increased by 78 days, and burn durations of fires greater than 1000 ha have increased from 7.5 to 37.1 days, in response to a spring-summer warming of 0.87 degrees C. Earlier spring snowmelt has led to longer grow­ing seasons and drought, especially at higher elevations, where the increase in wildfire activity has been greatest. In the south-western U.S., fire activity is correlated with ENSO positive phases [El Niños], and higher Palmer Drought Severity Indices."

By 2050, the United States will see wildfires twice as destructive as today, and some 20 million acres a year will burn, accord­ing to a 265-page federal report authored by scientists from the U.S. Forest Service. The December 2012 report found that in places such as western Colorado, which had experienced its worst wildfire ever that year, the area burned by midcentury could jump as much as fivefold.

Many other analyses on how climate change affects fire risk have come to similar conclusions. A 2012 research report by Climate Central scientists, “The Age of Western Wildfires,” found that compared to 40 years ago, the wildfire burn sea­son is two and a half months longer. The National Research Council has projected that for every degree Celsius the Earth’s temperature rises, the area burned in the western U.S. could quadruple. We are on track to warm 4 degrees C in the coming cen­tury. These findings are also in line with the observed impacts climate change is having on wildfires, where acreage burned is already on the rise.

A July 2015 study in Nature Communications, “Climate- induced variations in global wildfire danger from 1979 to 2013,” examined the worldwide impact climate change was having on wildfires. The researchers concluded that the length of the wildfire season had increased by almost 20 percent, and the global burnable area more than doubled, over that time period.

Forest Service scientists spelled out other effects climate change will have on North American forests. The Rocky Mountain forests will continue to become hotter and drier, which not only boosts wildfires but also infestations of insects such as the bark beetle, which has already devastated tens of millions of acres of U.S. and Canadian forests. The mountain pine beetle alone has already wiped out forests the size of Washington State, some 70,000 square miles of trees. Milder winters mean fewer beetle larvae die, and warmer spring and fall can double their mating season. At the same time, warm­ing allows bark beetles to extend their ranges to higher alti­tudes and more northern regions. The Forest Service report notes that in some cases, it appears the pine beetle can increase the risk of forest fires. The authors explain that one beetle out­break created a “perfect storm” in 2006 in Washington, where higher elevation lodgepole pines burned “with exceptionally high intensity.” Although climate change is clearly contrib­uting to the spread of bark beetles and the devastation they cause forests, recent studies offer differing views of whether beetle-infested trees have contributed significantly to the increase in wildfires.

For more from Joseph Romm, see:

Energy Conservation in Agriculture

Reprinted from CLIMATE CHANGE: What Everyone Needs to Know® by Joseph Romm with permission from Oxford University Press, Inc. Copyright © Oxford University Press 2016.