The southwest United States has already begun a long-predicted shift into a decidedly drier climate. 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.
Ten of California's 20 largest wildfires on record have all burned in the last 10 years, 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.
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." 
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.
Climate change has exacerbated naturally occurring droughts, and therefore fuel conditions.
- Robert Field, a research scientist at NASA’s Goddard Institute for Space Studies
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. The length of the fire season has expanded by 2.5 months, and the size of wildfires has increased severalfold. More than half the US Western states have experienced their largest wildfire on record since 2000.
Higher temperatures, reduced snow pack, and earlier onset of springtime are leading to increases in wildfire in the western United States, while extreme droughts are becoming more frequent. 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.
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. However, the fingerprint of global warming can be found in the pattern of increasing wildfire across the West.
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.