Wildfire in western U.S. federally managed forests has increased substantially in recent decades, with large (>1000 acre) fires in the decade through 2012 over five times as frequent (450 percent increase) and burned area over ten times as great (930 percent increase) as the 1970s and early 1980s. These changes are closely linked to increased temperatures and a greater frequency and intensity of drought. Projected additional future warming implies that wildfire activity may continue to increase in western forests. However, the interaction of changes in climate, fire and other disturbances, vegetation and land management may eventually transform some forest ecosystems and fire regimes, with changes in the spatial extent of forest and fire regime types. In particular, forests characterized by infrequent, high-severity stand replacing fire may be highly sensitive to warming. Increased wildfire combined with warming may transform these ecosystems such that fuel availability, rather than flammability, becomes the dominant constraint on fire activity. Climate will continue to warm for some time regardless of future greenhouse gas emissions, requiring adaptation to warmer temperatures. Changes in forest location, extent and type will result in substantial changes in ecosystem services.