Range distributions for many animal species across North America are shifting, many in directions consistent with anthropogenic climate change over the last century. Assuming climate change continues to act as a driver for geographic range shifts, theoretical northern range shift movements can be calculated using a bioclimatic envelope approach that assume the need to maintain current temperatures and determine whether these would be attainable given projected temperature changes over the coming century. We focus on historically present small mammals in northern Indiana whose range shifts from their 1930s capture locations are attributed to be a hypothetical “response” to changes in recorded and projected average January temperature from 1914–1944 to 1961–1990, 2020–2049, and 2070–2099. Over the mid-20th century, the theoretical distance a mammal must move to remain at the same temperature (temperature-maintaining distance, TMD) ranged from 18.6 to 97.3 km (0.40–2.07 km/year) and appears to have been attainable. However, based on future temperature changes projected under the SRES higher (A1FI) and lower (B1) emissions scenarios, we found significantly larger increases in TMDs by both mid- and end-of-century relative to the historical period. Given recognized barriers to northern range extension, future small mammal TMDs greater than 4 km/year in some scenarios appear less viable than those experienced in the past in this region. As differences between higher and lower emissions scenarios may ultimately influence the ability of mammals to move TMDs, particularly by the end of the century, future emissions have the potential to markedly affect the resulting range shifts.