Wildfire season has gotten almost 20 percent longer over the past 35 years worldwide as a result of rising global temperatures and fewer rainy days. In the United States, climate change has led to fire seasons that are now 78 days longer on average compared to 1970. U.S. wildfires have also seen significant growth, both in terms of acreage burned and in financial costs to property owners and communities. The 2015 fire season set a new record as the earliest the number of national acres burned reached more than 7 million. The U.S. Forest Service spent more than half its budget in 2015 preparing for and fighting fires, compared to just 16 percent in 1995. Average annual fire suppression costsincreased to $3 billion from $1 billion in the 1990s. By the early 2000s, the area burned each year doubled from 3.6 million acres to 6.5 million. A report places the average annual burned area in the U.S. between 7 and 9 million acres.

Climate change affects wildfire trends by influencing the variables that start or fuel fires, including ignition occurrence, fuel availability and flammability. For example, climate change may alter storm patterns, directly affecting the number of lightning-caused fires. Climate change may also lead to shifts in the composition and structure of forests, increasing fuel availability. Finally, changes in short-term climate variability such as higher temperatures, lower humidity and stronger winds can increase flammability and the spread of wildfires.

In the United States, climate change has amplified the threat of wildfires by increasing temperatures and the frequency of droughts, as well as by altering precipitation patterns. These changes have many consequences for wildfire behavior. Warmer temperatures have led to the occurrence of wildfires in new locations, such as arctic Alaska and the southwestern deserts. In addition, prolonged periods of record high temperatures associated with drought cause drier conditions that can increase wildfire size and extend wildfire seasons. This has been a problem in the western U.S., where the frequency of large wildfires and the length of the fire season have increased substantially in recent decades, largely due to earlier spring snowmelt and higher temperatures.

While fire risks are projected to increase globally, temperate forests in North America are among the regions most threatened by wildfires. In the U.S., the area that wildfires burn each year almost doubled from 3.6 million to 6.5 million acres from the 1990s to 2000s, with 9.5 million acres burned in 2006 and 9.1 million in 2012. A recent report places the average annual burned area in the U.S. between 7 and 9 million acres. In addition, nine of the ten years with the largest acreage burned occurred since the year 2000—coinciding with many of the warmest years on record—and the six worst fire seasons since 1960 have occurred since 2000. Over the next 25 years, the U.S. National Climate Assessment predicts the area burned by wildfires will double nationwide as global warming leads to higher temperatures, longer wildfire seasons and more frequent droughts. By the end of the century, models project that burned area in North America could increase by 2 to 5.5 times.

The following primer highlights emerging U.S. wildfire trends (with a particular focus on the West) and their connection to climate change, as well as wildfire impacts to human health and the economy.

Source: Wildfire today, Data: National Interagency Fire Center (NIFC).

Western states face the greatest threat

Across the western U.S., research indicates significant, increasing trends in the number of large fires and/or the total area burned per year. Trends are most significant in mountainous regions and the Southwest.

In the Southwest, seasonal and multi-year droughts have been shown to affect wildfire severity. Western states have seen an increase in the number of large wildfires at a rate of nearly seven large fires per year from 1984-2011, and the total burned area increased by 216 square miles per year for the same time period. The trends were most pronounced for southern and mountain regions, not coincidentally accompanied by an increasing trend of drought severity.

Research also indicates that climate outweighs other factors in determining where western wildfires occur and is largely responsible for extending the areas susceptible to wildfire activity. For example, the burn area in western U.S. mid-elevation conifer forests, like those of the Sierra Nevada Mountainsincreased by 650 percent between 1970 and 2003. What’s more, a new study quantifying the amount of carbon stored and released through California forests and wildlands finds that wildfires and deforestation contribute more than expected to the state’s greenhouse gas emissions, creating a positive feedback loop that increases the rate of climate change.

literature review of existing research on wildfire trends in the U.S. predicts a 50 percent increase in the area burned by 2050, with particular risks to Western states, with some studies predicting as much as a 100 percent increase. If we fail to reduce emissions, by 2085 California alone could experience a 36 to 74 percent increase in area burned.

Recent wildfire trends

California fires in 2015 were extremely volatile and spread rapidly due to ongoing drought and heat throughout the state. In 2014, California burned through its $209 million annual wildfire-fighting budget in the first three months of its fiscal year and was forced to tap into a reserve account for $70 million in additional funding. In 2013, the wildfires during the summer were extremely intense for some areas, especially the Rim Fire near Yosemite National Park that burned over a quarter of a million acres of forest. The Rim Fire was among the top three largest wildfires in California’s history, and is emblematic of this sort of increasingly common mega-fire. These examples are only some of the latest in an emerging trend. By one estimate, $4 billion was spent combating wildfires in California from 2003-2012, more than in any other state.

Source: Climate Central.

In Oregon and Washington, which have experienced record fire seasons in recent years, research shows a link between wildfire activity and climate change. According to the research, minimum temperature, average maximum temperature, and average dewpoint increased significantly after the 1990s, corresponding to “a significant increase in total hectares burned for the same time period.” In 2015, Washington had its worst wildfire season on record in terms of total acres burned, and the state saw its largest fire on record. Oregon also saw a record year in terms of the number of homes consumed by fire. In 2014, Oregon and Washington logged 4,567 fires that scorched 1,371,601 acres on federal, state and private lands. That’s 18 percent higher than the 10-year average of 3,877 fires in both states and almost three times greater than the 10-year average for burns, which is 452,039 acres. Washington's 256,108-acre Carlton Complex was the state's largest-ever blaze, while Oregon’s was the Buzzard Complex which burned 395,747-acres in southeastern Oregon. Further North, Western Canada got an early start to its 2015 wildfire season, with two large blazes forcing oil sands producers to curtail 230,000 barrels, or 10 percent of daily output, for several days. A study analyzing historical wildfires in Alberta, Canada, from 1961 through 2010, found the number of wildfires and average area burned grew during this time alongside temperature rise.

Source: LA Times.

While wildfire seasons have been more extreme out West, the U.S. as a whole experienced average wildfire seasons in 2013 and 2014, in terms of total acres burned (4.3 million in 2013 and 3.6 in 2014), and below-average seasons in terms of total number of fires. In 2014, there were 63,312 wildfires, which ranks second only to 2013 as the lowest annual number of wildfires over the past 20 years. However, just one year before, in 2012, more than nine million acres burned, the third highest total on record (behind 2006 and 2007) with damages topping $1 billion. Fire management also has a heavy influence on wildfire severity. One report’s explanation for the decreased number of U.S. fires and fewer acres burned in 2014 is a greater response to small fires, though this also means much greater costs.

Wildfire costs are increasing fast

In the 1990s, annual federal wildfire protection and suppression efforts cost on average less than $1 billion. Since 2002, the cost has risen to an average of more than $3 billion per year. Now more than half of the annual budget for the Forest Service and more than 10 percent of the budget for all Department of the Interior agencies goes to wildfire efforts. These figures do not include the $1-2 billion spent by states on wildfire protection or an untold amount spent by local governments. More severe fire seasons are part of the cause of the tripling of federal fire protection expenses, but it also results from more people building homes in and near forests and other wildernesses that are at risk from wildfires.

Federal wildfire appropriations to the Forest Service and Department of the Interior from 1994-2012. Source: Congressional Research Service Report, Headwaters Economics.

Research suggests that suppression costs are typically 10 to 50 times less than total wildfire costs. The  total cost of U.S. wildfires is presently estimated to be between $20 billion and $125 billion annually, while suppression efforts are roughly $2 to $2.5 billion. By 2050, climate change-induced wildfires will likely cost the U.S. between $10 billion and $62.5 billion annually, with a middle estimate of $22.5 billion. This amounts to as much as 0.36 percent of projected U.S. GDP.


Health impacts

The impacts of wildfire on human health are very solidly documented, with the increase in wildfire frequency worsening air quality and harmful health effects, according to the U.S. National Climate Assessment. Wildfire smoke contains particulate matter and toxins—including carbon monoxide, nitrogen oxides, and various volatile organic compounds that are ozone precursors—and can significantly worsen air quality, both locally and in areas downwind of fires for days or months. Increased particulate matter is “known to cause earlier mortality and morbidity by leading to cancer, respiratory problems (asthma, bronchitis, chronic obstructive pulmonary disease, reduced lung function, chest pain), discomfort (eye irritation, fatigue, headache, dizziness, and distress), cardiovascular effects, and depressed immune defenses (especially respiratory).”

It is estimated that there are 260,000 to 600,000 annual deaths globally from wildfire smoke between the years of 1997 and 2006. Harmful impacts on health are projected to increase as future climate change increases the risk of wildfire and its associated emissions.

Source: Wildfire today, Data: National Interagency Fire Center (NIFC).

Relevant Scientific Quotes

IPCC Fifth Assessment Report

“Since the mid-1980s large wildfire activity in North America has been marked by increased frequency and duration, and longer wildfire seasons (Westerling et al., 2006; Williamson et al., 2009). Recent wildfires in western Canada, the USA, and Mexico relate to long and warm spring and summer droughts, particularly when they are accompanied by winds (Holden et al., 2007; Comisión Nacional Forestal, 2012b).” (IPCC, AR5, WGII p.1460)

“Drought conditions are strongly associated with wildfire occurrence, as dead fuels such as needles and dried stems promote the incidence of firebrands and spot fires (Keeley and Zedler, 2009; Liu et al., 2012). Drought trends vary across regions (Groisman et al., 2007; Girardin et al., 2012): The western USA has experienced drier conditions since the 1970s (Peterson et al., 2013); drought periods in Alberta and Idaho have coincided with large burned areas (Pierce and Meyer, 2008; Kulshreshtha, 2011).” (IPCC, AR5, WGII p.1461)

U.S. Fifth National Climate Assessment

“Given strong relationships between climate and fire…projected climate changes suggest that western forests in the United States will be increasingly affected by large and intense fires that occur more frequently.” (NCA, p.178)

“Eastern forests are less likely to experience immediate increases in wildfire, unless a point is reached at which rising temperatures combine with seasonal dry periods, more protracted drought, and/or insect outbreaks to trigger wildfires – conditions that have been seen in Florida.” (NCA, p.178)

“[T]he increasing prevalence of extreme conditions that encourage wildfires can convert some forests to shrublands and meadows or permanently reduce the amount of carbon stored in existing forests if fires occur more frequently.” (NCA, p.181)

“Warming has also led to novel wildfire occurrence in ecosystems where it has been absent in recent history, such as arctic Alaska and the southwestern deserts where new fires are fueled by non-native annual grasses.” (NCA, p.200)