BILLINGS, Mont. (AP) – Climate change in the Western U.S. means more intense and frequent wildfires churning out waves of smoke that scientists say will affect tens of millions of people and cause premature deaths to spike. That’s prompting people in cities and rural areas alike to gird themselves for another summer of sooty skies along the West Coast and in the Rocky Mountains. Wildfire smoke was once considered a nuisance except for the most vulnerable populations. It’s now seen in some regions as a recurring public health threat. Harvard University climate researcher Loretta Mickley says residents of Northern California, western Oregon, Washington state and the Northern Rockies could see the most increases in smoke exposure. Microscopic particles in smoke can penetrate deeply into the lungs to cause coughing, chest pain and asthma attacks.