Hundreds of thousands of homes along U.S. coasts are at risk of devastating coastal flooding over the next 30 years as climate change causes oceans to rise, according to a new study. About 311,000 coastal homes, worth about $120 billion, are at risk of chronic flooding, the Union of Concerned Scientists, a science advocacy group, said in the report released Monday. By the end of the century, homes and businesses currently worth more than $1 trillion — including those in Miami, New York’s Long Island and the San Francisco Bay area — could be at risk.