Influence of Increasing Surface Humidity on Winter Warming at High Altitudes through the 21st Century I. Rangwala, J. Miller, G. L. Russell and M. Xu Surface Water Vapor Feedback (SWVF) Short Term Warming!!! “BL can become optically saturated in longwave” (Free Atmosphere) (Atmospheric Boundary Layer) Water Vapor Water Vapor Warmer Air DLR Longwave (4-200 µm) Land Surface DLR Surface Water Vapor Feedback (SWVF) Surface air has relatively low water vapor in high altitude and high latitude regions, particularly during WV WV WV WV the cold months. These regions could, therefore, Larger DLR increase Smaller DLR increase experience significant decadal-century scale warming Land Surface due to the surface-water vapor feedback DLR = Downward Longwave Radiation (W/m2) q = Specific Humidity (g/kg) Observations of SWVF from Swiss Alps Monthly means in DLR and q from 2001-2004 Jungfraujoch – 3584m, Locarno Monti – 388m Rucksthul et al., 2007 (JGR) Study Regions Tibetan Plateau San Juan Mountains, Colorado Tibetan Plateau (TP) Tibetan Plateau Late 20th Century Climate Change in the TP Largest warming during winter [Liu and Chen, 2000; Du et al., 2004; Chen et al., 2006; You et al., 2007] Winter warming at least twice as high as any other season [Liu and Chen, 2000] Tibetan Plateau Location & Elevation , n=29 105 Observations biased towards the eastern half and overall inadequate in describing the plateau! The Model GISS AOM (3 Latitude x 4 Longitude) Coupled Atmosphere – Ocean GCM (Russell et al. 1995; http://aom.giss.nasa.gov) Transient – SRES A1B for the 21st century 9 layers of atmosphere and 13 layers of ocean Time period: 1850 – 2100 (251 years) Model Validation for the Plateau Tibetan Plateau Observations (1961-2000): Seasonal Warming rate Tibetan Plateau 21st Century Warming Trend (oC/decade) 2001-2100 Higher Elevation 21st century: Changes in seasonal temperatures and surface energy fluxes Large increases in DLR Greater warming in Large increases in w.r.t. ULR Averages during winter Decadal winter and spring ASR during spring 2090s minus 2000s Tibetan Plateau Little change in ASR during winter DLR- downward longwave, ASR – absorbed solar radiation, LAT – latent heat, SEN – sensible heat, ULR- upward longwave Tibetan Plateau How much DLR change has occurred over the plateau due to changes in q in the late 20th century? Tibetan Plateau Modeled DLR vs Specific Humidity (q) Output from 1950-2100 Observed q: 1961-2000 Slope: Sensitivity of DLR to q (λ) Tibetan Plateau Estimated DLR Change (∆DLR) Between 1961-2000 ∆DLR = λ *∆q Where ∆q is observed change in q between 1961-2000 Largest DLR increases during winter and at higher elevations Tibetan Plateau Conclusions: TP Observations and the model experiment suggest large winter warming in the late 20th and 21st century Winter warming in the model occurs primarily due to increases in DLR caused, in part, by increases in q Consistent with other studies, the model suggests snow-albedo feedback to be an important cause for warming at higher elevations but during spring and summer Acknowledgements Observations – Data Ming Xu, Rutgers University Model Gary Russell, NASA-GISS AGU Travel Support