Last updated June 22, 2018

Wildfire Risk Increase

Climate change has increased the risk of wildfires primarily through warmer temperatures and drier conditions, which increase the chances of a fire starting and help a burning fire spread. Warmer and drier conditions also contribute to the spread of the mountain pine beetle and other insects that can weaken or kill trees, building up the fuels in a forest.

Scientists have observed a significant increasing trend in the number of large fires and the total area burned per year in the United States. In the West, anthropogenic climate change has been directly linked to increased forest fire and evaporation.[1]

Climate change and wildfire risk talking points

  • The world is getting warmer and that primes conditions for wildfires to start and spread more easily
  • With climate change, drier landscapes help fires start and spread more easily
  • Hotter temperatures throughout the year prolong fire season
  • Earlier snowmelt, temperature changes, and drought associated with climate change are important contributors to the increase in large and long fires

Global trends

A global analysis of daily fire weather trends from 1979 to 2013 shows that fire weather seasons have lengthened across 29.6 million km2—or 25.3 percent—of the Earth’s vegetated surface, resulting in an 18.7 percent increase in global mean fire weather season length.[1]

Nationwide trends

The National Climate Assessment states, “Hotter and drier weather and earlier snowmelt mean that wildfires in the West start earlier in the spring, last later into the fall, and burn more acreage.”[2]

  • Southeast: The southeastern US (including Texas and Oklahoma) leads the nation in number of wildfires, averaging 45,000 fires per year,[2] and this number continues to increase.[3][4] Increasing temperatures contribute to increased fire frequency, intensity, and size,[2] though at some level of fire frequency, increased fire frequency would lead to decreased fire intensity. Lightning is a frequent initiator of wildfires, and the Southeast currently has the greatest frequency of lightning strikes of any region of the country.[2] Increasing temperatures and changing atmospheric patterns may affect the number of lightning strikes in the Southeast, which could influence air quality, direct injury, and wildfires.[2]
  • Northwest: A 2006 study found a statistically significant relationship between warming in the North Pacific and all the major wildfire events in the northwestern US from 1980-2002.[5]
  • Alaska: A 2016 attribution analysis indicated that Alaskan fuel conditions during the 2015 fire season were 34%–60% more likely to occur in today’s anthropogenically changed climate than in the past.[6]
  • Great Plains: A 2017 study found that the total area burned by large wildfires in the Great Plains rose 400% over a three-decade study period (1984-2014).[7] The study also found that the average number of large wildfires in the biome increased from 33.4 ± 5.6 per year from 1985 to 1994 to 116.8 ± 28.8 wildfires per year from 2005 to 2014.[7]
  • West: Higher temperatures, reduced snow pack, and earlier onset of springtime are leading to increases in wildfire in the western United States,[9] while extreme droughts are becoming more frequent.[8] Climate change is also affecting the prevalence and distribution of pine beetles, because warmer winter conditions allow the beetles to breed more frequently and successfully.[9][10] According to the US National Academy of Sciences, over the past 30 years, there has been a fourfold increase in the number of large and long-duration forest fires in the American West.[11] The length of the fire season has expanded by 2.5 months, and the size of wildfires has increased severalfold.[11][12] Additionally, more than half the US Western states have experienced their largest wildfire on record since 2000.[12]

California trends

The southwest United States has already begun a long-predicted shift into a decidedly drier climate.[13] The shift has increased wildfire risk in California through higher temperatures, intensified drought, earlier spring snow melt, pine beetle infestations linked to warmer winter conditions, and tree die-off. Extreme heat and years of ongoing drought are both linked to climate change and are increasing wildfire risk throughout California by contributing to the frequency and severity of wildfires in recent decades.[13]

Fourteen of California's 20 largest wildfires on record have all burned since 2000[14], while pine beetles, heat and California’s five-year drought have caused 66 million trees to die in the state’s Sierra Nevada forests since 2010.[15]

A formal modeling analysis has identified the fingerprint of global warming in California's wildfires, reporting that  "an increase in fire risk in California is attributable to human-induced climate change."[16]

Study of southern California wildfires has found the weather conditions (e.g. unusually hot local temperatures) are the primary driver of the size of spring and summer fires in these landscapes.[17]

Climate change has exacerbated naturally occurring droughts, and therefore fuel conditions.

- Robert Field, a research scientist at NASA’s Goddard Institute for Space Studies[18]

The role of fire management practices

In addition to climate change, historic fire suppression has played a role in current wildfire activity.  Both factors are at play. Past fire suppression has led to changes in fuels, fire frequency, and fire intensity in some southwestern ponderosa pine and Sierran forests but has had relatively little impact on fire activity in portions of the Rocky Mountains and in the low-lying grasses of southern California.[19] However, the fingerprint of global warming can be found in the pattern of increasing wildfire across the West.[20]

Changes in firefighting practices over time—such as more frequent use of intentional burning to clear fuels as a fire suppression tactic—may have had impacts on the boundaries of burn areas, but generally, the effects of human development vary regionally, in some cases increasing fire activity and in others decreasing it.[19]