Analysis of 7 GCM simulations with 2x CO2 levels shows large and statistically significant free air temperature changes (compared to controls) along the axis of the American Cordillera (from Alaska to southern Chile). At all latitudes, the modeled change in temperature increases with elevation. Temperature increases are especially large in boreal summer months from ~35--50¿N, and year-round in the high mountains of Peru, Bolivia and northern Chile. If these models are correct, mountain ranges that extend high into the lower troposphere are likely to experience significant warming, with implications for glacier mass balance and water resources, montane ecosystems and high elevation agricultural activities. There are few high elevation meteorological stations to validate the model projections, or to monitor future changes. The planned GCOS (Global Climate Observing System) surface network is not adequate to address the critical issues raised by these model simulations; additional high elevation observing stations are needed.