We collected 39 days of instrumental temperature records and combined them with forest density data obtained from remotely sensed imagery, to develop two temperature models: one of the modern forest, and one of an extrapolated undisturbed landscape that predates large-scale logging, in a 15 km x 20 km area of the Cascade Range of Washington. The modeled temperature difference between the modern and undisturbed landscape is 0.8°C. Using a first-order model of glacier length change, this temperature perturbation is estimated to result in up to 0.66 km of glacier retreat. Over the past few centuries, it has been observed that the large Cascade glaciers have retreated between 2.0 and 2.5 km. The results of this study account for a substantial amount of recent glacier retreat that is often attributed to anthropogenic warming from increased greenhouse gases.