Charles Warren Thornthwaite (March 7, 1899 – June 11, 1963) was an American geographer and climatologist. He is best known for devising the Thornthwaite climate classification, a climate classification system modified in 1948 that is still in use worldwide, and also for his detailed water budget computations of potential evapotranspiration. He was Professor of Climatology at Johns Hopkins University, adjunct professor at Drexel University, President of the Commission for Climatology of the World Meteorological Organization, a recipient of the Outstanding Achievement Award of the Association of American Geographers, and the Cullum Geographical Medal from the American Geographical Society. Life Thornthwaite was born in Bay City, Michigan. He attended Central Michigan Normal School, graduating in 1922. He taught at high school for the next two years in Owosso, Michigan, then for the next four years he was employed as a geographer for the Kentucky Geological Survey. While there, he also became an assistant professor in the University of Oklahoma Department of Geography, serving there from 1927 to 1934. Meanwhile, he studied geography through the auspices of the University of California, Berkeley, a student of Carl Sauer. In 1930 he received a Ph.D. in geography; his thesis was on "Louisville, Kentucky: A Study in Urban Geography", a research project which used aerial photographs, field observation, data analysis and detailed mapping to describe the urban geography of Louisville. He moved away from geography to climatology, but recent scholarship suggests he was nonetheless ahead of his time in his thesis project and that many of the techniques he used would later be standard procedures. At Central Michigan Normal School, Thornthwaite befriended John Leighly. Later, they both studied at Berkeley, with Leighly becoming his mentor. Leighly, a professor at UC Berkeley for 62 years, would write his obituary. In 1931 Thornthwaite published “The Climates of North America: According to a New Classification”, which launched his career as a climatologist and married the science of climatology with that of geography. In 1934, he left the University of Oklahoma to study internal migration within the United States at the University of Pennsylvania. In 1935, he was appointed chief of the climatic and physiographic research division of the U.S. Soil Conservation Service in the U.S. Department of Agriculture. The division ceased to function in 1942, but he remained on staff of the USDA until 1946. Included in his output from this period was the USDA technical bulletin, written