This award supports a study to develop the numerical modeling techniques necessary to infer past surface temperatures from temperature profiles measured in ice core boreholes. Control theory, a branch of applied mathematics will be used to recover this information. Once the techniques are developed and adequately tested on data from the Dye 3 borehole, these methods will be applied to the temperature data to be obtained from the GISP2 borehole at Summit, Greenland. This work will help to provide an independent check on interpretations of isotopic signals measured in ice cores.