High temperatures. Low humidity. Little rainfall. Dry vegetation. Fast winds.

Wildfires depend on a combination of environmental conditions to start and spread. As global temperatures rise, research shows these conditions are appearing more intensely and frequently — escalating the risk of wildfires.

This summer, the United States has suffered through record-breaking heat, destructive fires and stifling smoke. Wildfires have burned more than a million acres in at least 12 states. Anomalously high temperatures and extremely dry conditions, particularly in the western United States, are expected to exacerbate fire conditions into the fall.