Coal's contribution to air pollution can be tracked in soot-covered birds

Field sparrows from 1906 (top) and 1996 (bottom). The top bird is covered in soot. Photo: PNAS

Comparing the feathers of songbird specimens collected in the Rust Belt over 135 years, researchers at the University of Chicago report there was more soot in the air during the early 20th century than originally estimated.

Why it matters: Soot or black carbon from burning coal contributes to climate change but is difficult to study because it falls out of the atmosphere after a few days or weeks. Researchers want to be able to accurately assess soot's role in past warming in the past in order to improve predictions about future contributions.