Wildfires and climate change

Top Line

Human-caused climate change is a significant contributor to the increasing size, intensity, and damage of western U.S. wildfires, and to a lengthening of U.S. fire seasons.

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• The frequency and intensity of wildfires in Alaska have been greater in the past few decades than for any period in the past 10,000 years.11
• Some populations are disproportionately at risk from wildfires. U.S. census tracts populated primarily by Black, Hispanic, or Native American people have roughly 50% more wildfire risk than do other census tracts.12
• More and bigger wildfires means more toxic smoke exposures. Computer models have estimated that, over the past decade, the number of people experiencing at least one day of wildfire smoke levels deemed unhealthy for all age groups increased 27-fold, with nearly 25 million Americans so exposed in 2020 alone.13 Other analyses have suggested that wildfire smoke may have a bigger impact on health and lead to more respiratory hospitalizations than smoke with similar particle sizes from other sources.14

Pitfalls to Avoid

Many factors contribute to wildfire occurrences, and human activities are by far the leading source of wildfire ignitions even as climate change has contributed significantly to wildfire size and intensity. (From 1992 to 2012 in the United States, humans ignited 84 percent of wildfires.15) Instead of asking whether climate change "caused" a wildfire, it's better to ask:

• How is climate change influencing the likelihood of wildfires such as these?
• To what extent was this wildfire larger and/or more intense because of climate change?
• How has climate change made the U.S. more vulnerable to large fires like this one?