Interior Alaska (2015) and Northwest Territories (2014) recently experienced large fire seasons. Most of the burned area is from fires that ignited before July. Drought-induced early season (June) lightning ignitions were an important driver of these large fire years. Ignition density is at least equally important in explaining annual burned area than fire size. Future climate predictions show increases in vapor pressure deficit that will drive increases in ignitions, fire size and annual burned area by 2050-2074. Ignitions and burned area are likely to occur more frequently close the latitudinal treeline. This may accelerate the northward migration of tree species and thereby induce a biome shift.