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