Fields of sand dunes present some of the most intriguing patterns seen on Earth and other planets, such as Mars. The dunes form when wind transports sand grains, causing them to pile up into small mounds that eventually evolve into the graceful shapes that adorn calendars and postage stamps. The characteristics of the wind, such as its direction and the supply of sand, are imprinted on the pattern of dunes in such a way that it is possible, just by carefully examining the dune pattern, to say something about the climatic conditions that lead to its creation. As winds and sand supply change through time, the pattern of dunes slowly changes as well in ways that are not yet fully delineated. The information about climate over the past thousands to tens of thousands of years stored in the great sand dune fields of Africa, the Middle East, Asia, Australia and North America might provide critical understanding in predicting the reaction of regional climates and landscapes to human-induced global climate change. PIs aim is to develop a methodology for inferring past climate from dune patterns and to apply it to three natural dune fields. To achieve this goal, they have developed numerical models that span the range of time periods over which dunes and dune fields can react to changes in climate: (1) a model for the overall characteristics of dune fields, including spacing between dunes and their orientation (thousands of years); (2) a model for the motion of the trace of the tops of dunes, their crestlines (hundreds of years); and (3) a model for the changes in shapes of dunes (tens of years). These models will be used to investigate the development of the Algodones dune field in southeastern California, the dunes of the Namibian desert in western Namibia, and the dunes of the deserts of western Mauritania. The interpretations PIs derive regarding past climate will be tested by attempting to recreate the patterns of these three dune fields using their climatic inferences in a wind tunnel filled with sand.