Their predictions show that the number of “runaway” fires (the small proportion of blazes that escape initial firefighting efforts and go on to ravage large areas) will double in northern California when carbon dioxide doubles in the Earth’s atmosphere—a threshold climate scientists expect the planet to cross later this century. This increase of 114 runaway fires yearly will kill more people, destroy more property and wildlife habitat, worsen air and water quality, cause floods and mudslides on destabilized hillsides and drive up the costs of firefighting and insurance. In addition, increased fires will change the ecology of northern California, as grasslands and scrub forests replace tree stands.