Martha’s Vineyard and Nantucket are facing serious impacts from rising sea levels and more powerful coastal storms driven by climate change, a new environmental reportwarns. The “State of the Coast” report by the Trustees, a prominent Massachusetts conservation group, says the popular tourist destinations off Cape Cod risk losing hundreds of acres of marshlands to flooding and billions of dollars in coastal homes, buildings and infrastructure to erosion. What’s more, roughly 900 structures on the two islands may experience daily tidal flooding by 2050 as sea levels are predicted to rise more than 2.5 feet (0.76 meters), the organization said. “The impacts of flooding and erosion on these beloved islands will affect thousands who live and work there, and the thousands more who visit each summer,” said Tom O’Shea, a managing director at the Trustees.