Earth system scientists have recently concluded that anthropogenic induced climate change is detectable. Because many aspects of an organism's ecology and evolution are influenced by environmental temperature, this suggests temperature mediated changes may be already occurring in natural ecosystems. Using archived mammal trapping and meteorological data, we investigated local changes in climate over the past 8 yr at the Sevilleta National Wildlife Refuge in an arid region of New Mexico to determine i) if environmental conditions had altered, ii) if mean body mass of woodrats had changed over this time period, and iii) if the answers to i) and ii) were positive, were the results correlated? Body mass was chosen because it is highly sensitive to temperature and many crucial ecological and evolutionary parameters are affected by it. Our results indicate that winter temperature measures (average cold and minimum), and maximum summer temperature have changed significantly over the past 8 yr. Summer and winter temperatures have both increased by ca 2.5 to 3°C. When compared to long-term means, all years have had significantly warmer than average minimum temperatures. Mean body mass of woodrat populations has also changed significantly over the past 8 yr, and the changes are negatively correlated with both winter and summer temperatures. We predict that additional climatic warming will lead to further decreases in the mean body mass of woodrats at the Sevilleta NWR. Since many important ecological parameters are tightly linked with body mass (e.g. fecundity, dietary strategy, home range, extinction rates, energetic requirements, predation risk, etc.), our results suggest that further climate change may lead to profound alterations in woodrat life history, and indirectly, on the dynamics and Structure of the entire community. This is in addition to any direct effect temperature may have on other plants and animals.