Forests soak up a lot of carbon dioxide that would otherwise contribute to climate change. But a new study by the U.S. Forest Service shows cities can store carbon too, as long as they maintain their urban tree canopy. Researchers tallied 708 million tons of carbon stored in urban trees across the U.S., and they put a value on that storage too: $50 billion in environmental services including reducing atmospheric carbon dioxide. In the study published recently in the journal Environmental Pollution, Dave Nowak, a research forester with the U.S. Forest Service's Northern Research Station, and his colleagues used urban tree field data from 28 cities and six states and national tree cover data to estimate total carbon storage in the nation's urban areas.