Scientists say climate change, degraded ecosystems and the fickleness of the weather have been amplifying fires in forests, grasslands and neighborhoods throughout the West. Nine times more western forestland is burning in large fires each year on average now than 30 years ago, according to calculations by two leading scientists.

The blazes create smoke waves — pulses of pollution containing everything from charred plastic residue to soot to other small particles that lodge deep in the lungs. They can trigger short-term ailments, such as coughing; worsen chronic diseases, such as asthma; and lead to long-term damage, including cancer.

The effect of last month’s fires in Northern California’s wine country, which destroyed thousands of homes and killed 43 people, spread well beyond the burn zone. The smoke choked the San Francisco Bay Area, home to 7 million people in nine counties, for days.

For more on this story, read John Upton and Barbara Feder Ostrov’s “Breathing Fire: Health Is A Casualty Of Climate-Fueled Blazes.”