The effects of climate change on environments are increasingly obvious and are leading to stronger and more varied biological responses as organisms compensate. To understand better the responses of terrestrial ectotherms to climate oscillations we created a biophysical model based on the degree-days concept to predict relevant life-history events. By studying side-blotched lizards, Uta stansburiana, we were able to calculate the timing and length of the growing season as well as the timing of the breeding season for this species at a site in the Pacific Northwest based primarily on temperature data. We then used historical meteorological data to test for the effects of short- and long-term fluctuations in climate modes on lizards using indices for the El Niño-Southern Oscillation (ENSO) and the Pacific Decadal Oscillation (PDO). Results indicate that these two climate modes affect different aspects of life history and that their effects, either alone or in combination, have the potential to alter not only phenology (e.g., timing of reproduction) but also population recruitment and even persistence. Yet, using these climate modes to predict biological outcomes of future climate change may be difficult to accomplish due to regional variation of their impacts and their inherent complexity.