Köppen was a prolific scientist, producing more than 500 papers, and he retained his intellectual curiosity and wide range of interests throughout his life. In 1890, he co-authored the first cloud atlas. Alongside scientific pursuits, he was actively involved in social questions, devoting much time and energy to such problems of land-use and school reform and nutrition for the underprivileged. He was a strong advocate for the use of Esperanto in the cause of world peace, translating several of his publications into Esperanto.