Boris Palmer, mayor of Ann Arbor’s sister city of Tübingen, Germany, will be at the downtown Library to discuss Climate Change and the City on Tues., May 13 at 7 pm. Known as Germany’s “greenest” mayor, Palmer started an unprecedented climate protection campaign at the local level during his first year in office. He will head a delegation of 29 Tübingen citizens visiting Ann Arbor, May 10-16.