His research focuses on environmental change in times of crisis and conflict. He is currently working on his book project, A Global Environmental History of the First World War, which is under contract with Cambridge University Press. He has received fellowships from the American Council of Learned Societies, the Austrian Ministry of Science and Research, the European Commission, the German Academic Exchange Service, and the National Endowment for the Humanities. Keller has given invited lectures in Africa, India, Turkey, across Europe, and throughout the United States. He earned his B.A. in History at the University of Rochester and his M.A. in German and European Studies and Ph.D. in History at Georgetown University.