Climate Feedbacks that Contribute to Enhanced Warming Rates at High Elevations

During the last several decades, many high elevation regions have been warming at faster rates than their lower elevation surroundings. Using a combination of ground-based observations, satellite retrievals, and model simulations, we analyze feedbacks associated with three different climate variables in three different mid-latitude regions that might contribute to these faster warming rates during the last three decades and as well as for model projections later this century. The climate variables include specific humidity, snow cover, and clouds with a particular emphasis on their effects on both surface downward longwave radiation (DLR) and shortwave radiation. The three regions from highest to lowest elevations are the Tibetan Plateau and surrounding mountains, the Colorado Rocky Mountains, and the northeastern United States. The model simulations are from the Coupled Model Intercomparison Project - Phase 5 (CMIP5). Both observations and models indicate that the sensitivity of DLR to changes in specific humidity is non-linear and larger when the atmosphere is drier, conditions that tend to occur at higher elevations during winter. The model projections for the 21st century indicate that the snow-albedo effect contributes to enhanced warming in the Tibetan Plateau and surrounding high-elevation regions. The multi-model CMIP5 ensemble indicates that warming rates globally will be enhanced at high elevations relative to their lower elevation counterparts in the northern hemisphere mid-latitudes, an effect that is stronger for daily minimum temperatures during the cold season, particularly in the Tibetan Plateau/Himalayan region. Satellite retrievals of cloud cover and cloud optical thickness are used to determine how they contribute to these feedbacks.