A paleoclimatologist, Caspar Ammann studies climates of the past centuries and millennia, including the Little Ice Age and the Medieval Warm Period. His goal is to understand what caused climatic changes in the past in order to learn more about potential global warming in the future. He uses computer models to simulate climate history and compares the results to historical markers such as tree rings and ice cores to reconstruct the past. His research also looks at changes in the Sun's output, the influence of volcanoes on climate, and the extent to which 20th century warming is unprecedented in the recent geologic timescale. He is a researcher in NCAR's Research Applications Laboratory.