C32B-01 INVITED
Climate Change Projections for the Tropical Andes Using Multiple Emission Scenarios: Implications for Future Glaciation and Water Resources
Observations on glacier extent in the tropical Andes give a detailed and unequivocal account of rapid shrinkage of tropical Andean glaciers since the Little Ice Age. Future climate change will likely continue to affect high-elevation tropical mountain regions more strongly than their surrounding lowlands. Increasing temperature and changes in precipitation patterns will affect the size and distribution of glaciers and wetlands, ecosystem integrity, and water availability for human consumption, irrigation, mining and power production. With this looming threat for future water supplies in the tropical Andes, discussions about adequate adaptation and mitigation strategies abound. Yet detailed projections of future climate change in the tropical Andes, which should form the basis for any such measure, are not yet available. Here we will present first results for the end of the 21st century (2071- 2100) using a regional climate model based on two different emission scenarios (A2 and B2). Our results indicate significant warming in the tropical Andes, ranging from 2° C to 7° C, depending on location and scenario considered. The warming is enhanced at higher elevations and further amplified in the mid-and upper troposphere. Temperature changes are spatially similar in both scenarios, but the amplitude is significantly higher (up to 3° C) in A2. The A2 scenario also shows a significant increase in interannual temperature variability, while it remains almost unchanged in B2 when compared to a 20th century control run. Inspection of the annual mean temperature probability density function for both slopes of the Andes further reveals that there is no overlap between mean annual temperature of either of the two future scenarios with a control run. In both cases the coldest temperatures projected for the years 2071-2100 are much higher than the warmest years in the modern control run (1961-90). Changes in precipitation are spatially much less coherent, with both regions of increased and decreased precipitation across the Andes. These results provide a first attempt at quantifying future climate change in the tropical Andes and could serve as input for impact models to simulate anticipated changes in Andean glaciation, hydrology and ecosystem integrity. In particular these simulations could help to analyze future changes in streamflow seasonality which might affect the water availability downstream due to the reduction of the glacial buffer during the dry season. They could also be used to assess for how long current glacier retreat and mass loss will add to a temporary increase in runoff, a process that raises sustainability concerns as downstream users quickly adapt to the temporary water surplus.
C32B-02
Hydrologic Transformation from Glacier Volume Loss in the Cordillera Blanca, Peru
Tropical Andean glaciers occupy an important nexus between physical and human dimensions of global climate change because they are both sensitive indicators of climate changes and critical hydrologic reservoirs in highland regions. These glaciers are undergoing rapid retreat with potentially devastating consequences for populations who rely on them for water resources. However, efforts to quantify and evaluate the implications of these changes to the hydrological cycle are hampered by a lack of continuous discharge and precipitation measurements. We have synthesized hydrochemical data from synoptically sampled glacier melt water, groundwater, precipitation, and stream discharge collected intermittently between 1998 and July 2008 throughout the Callejon de Huaylas, a 5000 km2 watershed that drains the western side of the Cordillera Blanca in northern Peru. We estimate an average increase of 1.6 (± 1.1) % in the specific discharge of the glacierized catchments as a function of changes in stable isotopes of water (δ18O and δ2H) from 2004 to 2006. These results confirm predicted short-term increases in discharge as glaciers melt, demonstrated by a significant (P<0.0005) positive trend in a 42- year discharge anomaly record from a glacier catchment (>20% glacierized area). We also use an end member mixing analysis based approach, called the hydrochemical basin characterization method (HBCM), to quantify the contribution of glacier meltwater, ground water and surface runoff to streams for different valleys and nested watersheds. The HBCM results show good agreement with measured stream discharge (maximum R2 of 0.99) for monthly cumulative values. The results suggest that, for most of the studied years, groundwater is the main contributor to basins outflow during the dry season but this contribution is subject to large variations. For example the dry-season groundwater contribution from a 7.2% glacierized valley in the Querococha Basin on the 1998-1999 and 2004-2007 periods averages 54% but varies between 16% and 74% on a year to year basis. The amount of melt water in the total discharge is directly influenced by the ice covered area and the hypsometric profile of glaciers within a watershed.
C32B-03
Rapid Ice Loss on Kerguelen Islands (Indian Ocean, 49S)
Due to their remoteness, the recent evolution of glaciers and ice caps on sub-Antarctic islands is poorly known. The objective of our study is to assess the changes of some of these austral ice masses located on the Kerguelen Islands (Indian Ocean, °S) using historical information (map published in 1967, glaciological campaigns carried out in the 1970s) and recent (1991-2007) satellite data from various sensors (Landsat, SPOT, SRTM, ICESat). Our analysis reveals that all glaciers have retreated between 1963 and 2003. Overall, the total ice-covered area declined from 703 to 552 km2, a reduction by 22%. The area of the Cook ice cap (the main ice body) has decreased from 501 to 403 km2. After 1991, the retreat rate of the Cook ice cap has accelerated, from 1.9 km2/yr (1963-1991) to 3.8 km2/yr (1991-2003). We have also determined the global ice volume loss of the ice cap using three independent and consistent estimates. Between 1963 and 2000, the total ice loss reaches 25-30 km3, equivalent to a very high area-average ice thinning rate of 1.4-1.7 m/yr. The glacial retreat took place in a climatic context of a relatively low level of precipitation (compared to the fifties) and a °C warming that occurred mainly between 1964 and 1982. The acceleration of the ice losses since, at least, the 1990s indicates that the ice masses on Kerguelen Islands are still far from their state of balance. Together with other studies in Patagonia, South Georgia and Heard Island, we contribute here to draw a homogeneous picture of strong and accelerated wastage of all ice masses influenced by the Austral Ocean.
C32B-04
Advancing Glaciers and Positive Mass Anomaly in the Karakoram Himalaya, Pakistan
Himalayan glaciers are thought to be extremely sensitive to climate change given their altitude and supraglacial debris characteristics. Limited field and space-based assessment of glaciers in the Karakoram suggests that these glaciers may be responding differently to climate forcing compared to rapidly retreating glaciers in the eastern Himalaya. Relatively little is known about glacier sensitivity to climate forcing in the western Himalaya. Consequently, we conducted an extensive investigation of glacier fluctuations in the Karakoram Himalaya of Pakistan, which is part of the international Global Land Ice Measurements From Space (GLIMS) project. Our specific objective was to estimate average retreat rates and ascertain the regional mass balance. To accomplish this, we utilized a variety of multi-temporal imagery including ASTER (Advanced Spaceborn Thermal Emission and Reflectance Radiometer), Landsat ETM (Enhanced Thematic Mapper), and declassified satellite imagery (KH-9), acquired from approximately 1980 to 2004. Climate reanalysis data sets (NCEP/NCAR and ERA40) and TRMM (Tropical Rainfall Mapping Mission) data were also utilized to examine precipitation patterns. We sampled approximately 250 glaciers in the region. Our result indicate that 65 percent of the glaciers either advanced or showed no change in terminus position. We also discovered a glacier surge anomaly and have identified and mapped 53 new surging glaciers that have not been previously reported. Paleoclimate proxies and climate data indicate that the region has experienced a general increase in precipitation over time. Satellite observations and climate data strongly suggest a regional positive mass balance. Direct confirmation of this has been determined from an analysis of GRACE (Gravity Recovery And Climate Experiment) gravity field data, which depicts a positive mass anomaly that is spatially coincident with advancing and surging glaciers, caused by increasing snowfall. Regional climate simulations using MM5 indicate that the mass anomaly is located at the confluence of the Westerlies and the southwest Asian Monsoon. The circulation and precipitation dynamics have been found to be influenced by ENSO, and support temporal variations in GRACE mass estimates. These new results clearly demonstrate that the glaciers in the Karkoram are behaving differently than the general world pattern of rapid glacier retreat.
C32B-05
Controls on Greenland Outlet Glacier Sensitivity to Climate Forcing: A Comparative Approach
Significant changes in the dynamics of Greenland's marine-terminating outlet glaciers
within the past few years indicate a rapid and complex response of these systems to recent climatic forcing.
Widespread and substantial accelerations in glacier flow-speed along Greenland's
southeast coast have been linked to destabilization and retreat of glacier fronts triggered by thinning to
flotation. There is concern that ongoing coastal thinning in northern Greenland will trigger a similar response,
further threatening the stability of the ice sheet. Despite regional ice thinning and retreat, the glaciers of
Greenland's northwest coast have not yet undergone substantial acceleration. This
suggests a lessened dynamic sensitivity of these glaciers to changes at the ice front than southeastern
glaciers, likely due to differences in glacier geometry. To investigate the potential factors behind this
contrasting behavior, we derive time series" of front position, ice thinning, and flow
speed for approximately 70 outlet glaciers along Greenland's southeast and northwest
coasts. Using these data, we look for patterns in the relationships between retreat, thinning, acceleration
and geometric variables, such as surface slope, to determine the first-order controls on sensitivity to changes
at the ice front. Based on these controls, we assess the future stability of these glaciers under continued
climate warming.
http://www.bprc.osu.edu/GDG/
C32B-06
Southern British Columbia Glacier Behavior Over the Past 29 Years
Small glaciers and ice caps represent the largest contribution to the rate of sea level rise and will continue to do so over roughly the next century. The glaciers in western North America are a major component of this highly responsive cryospheric component. We present a 200 m spatial resolution, regional simulation of the coupled mass balance/ice dynamics for the glaciers in southwest Canada and northern Washington as a whole. Our modelling is driven by high resolution mass balance estimates based on downscaled data from the North American Regional Reanalysis meteorological data set (Anslow, F. et al., Session C20, AGU FM 2008). The chosen model region contains numerous verification timeseries of glacier behavior and surface mass balance. We use these data to present comparison of our modelled glacier evolution with measured mass balance time series, and histories of glacier extent. Our model approach allows directly coupling of regional climate models with models of the cryosphere, and might eventually be extended to include snow cover and hydrological routing models.
C32B-07
Glaciers along the Copper River, Alaska, Controlled by Landslides, Vegetation, Lakes, Rivers (and Climate)
98% of glaciers in Alaska are retreating or thinning at low elevations due to warming; some are thickening at
high elevations due to rising precipitation. Anomalous surge and tidewater glaciers are much studied.
Debris-covered, freshwater-calving glaciers and juxtaposed land-terminating glaciers have their own peculiar
dynamics, as exemplified by glaciers in the Copper River corridor, Alaska. Those glaciers are losing area
and mass, consistent with Alaska's general trend and recent climate change. Other factors can exceed or
negate climatic influences on individual glaciers or parts of glaciers. For example, the terminus of Childs
Glacier has been almost stable for a century due to thermal/mechanical buffering by undercutting and calving
in the Copper River. Thick debris insulates glacier ice and retards glacier thinning and retreat. This
protective effect is enhanced when vegetation becomes established on glacier debris cover and cools the
glacier's surface. However, debris and vegetation also impedes drainage and can cause runaway lake
growth. Further complexity is caused by unsteady inputs of landslide debris, size-dependent glacier
response times, and influences of ice-contact lakes on glacier energy balance. Landslides can load and
accelerate glaciers in the first years afterward, and on century time scales thick debris insulates and
promotes vegetation growth, which first tends to stabilize glaciers, but the debris and vegetation eventually
induce supraglacial ponding, lake growth and glacier disintegration. Allen Glacier exhibits composite effects
of (1) calving into the Copper River at the peak of the Little Ice Age, (2) slow response to the termination of
the Little Ice Age; (3) landslides, debris insulation, and vegetational cooling; (4) nonlinear lake growth; and
(5) decades of warming climate, renewed melting, and disarticulation.
http://www.glims.org
C32B-08
Has dynamic thinning switched off in south-east Greenland?
Following a relatively stable period during the 1990s, dramatic changes have been reported for many
tidewater outlets in SE Greenland. Some of the most important results come from measurements using the
GRACE (Gravity Recovery and Climate Experiment) mission (1, 2). These data clearly identified the SE of the
Greenland Ice Sheet (GrIS) as having the highest rates of mass loss. Two of the major outlet glaciers in this
area, Helheim and Kangerdlugssuaq accelerated by about 100% and 40%, respectively, and their calving
fronts retreated by several km (3, 4). Retreat and acceleration occurred in two phases during summer 2003
and 2005 at Helheim, and in a single period between late 2004 and early 2005 at Kangerdlugssuaq. Further
south, widespread glacier acceleration between 1996 and 2005 affected most of the outlet glaciers, and
Greenland's mass loss doubled in the period (5). Increased discharge due to thinning in the marginal areas,
coupled to rapid changes in ice dynamics and synchronous retreat of calving front positions, led to
speculations that the GrIS had crossed a "tipping point" induced by global warming. However, subsequent
studies in summer 2006 showed that Helheim and Kangerdlugssuaq had simultaneously slowed down again
and thinning stopped (6).
In summer 2007, we collected lidar data over Helheim and Kangerdlugssuaq flown by the NERC Airborne
Research and Survey Facility. Data collected were single swaths over mountain areas, as well as centerline
profiles. In cooperation with NASA Goddard Space Flight Center, we conducted a similar but extended
campaign in 2008, collecting lidar and radar data for the 16 largest outlet glaciers in SE Greenland, targeting
the full extent of the major GRACE anomaly. We used lidar swaths from bedrock as ground-control for
extracting DEMs from ASTER satellite images covering the period with major changes in 2004 to 2006, and
compared them to lidar and SPOT 5 DEMs to produce the most recent volume change and velocity
estimates. Velocity estimates for the glaciers are derived from the ASTER and SPOT data, as well as
repeated lidar profiles. To place the contemporary findings in a broader temporal context we use aerial
photographs from the 1980s to extract the calving front positions of all targeted glaciers. The position of the
calving front of marine terminating outlets appears a good indicator for their behaviour, as all recent dynamic
changes were accompanied by large fluctuations in terminus position. For the first time, we will characterise
multi-decadal glacier changes for SE part of Greenland, aiming to answer the questions: (i) Has mass loss
slowed in the whole SE of Greenland and dynamic thinning switched off? (ii) Do recent changes in SE
Greenland outlet glaciers represent profound alterations in the ice sheet, or are they simply expected short-
term variability?
(1) Chen JL et al. Science 313 (2006).
(2) Velicogna I Wahr J, Science 311 (2006).
(3) Howat IM et al. Geophys. Res. Lett. 32 (2005).
(4) Luckman A et al. Geophys. Res. Lett. 33 (2006).
(5) Rignot E, Kanagaratnam P, Science 311 (2006).
(6) Howat IM et al. Science 315 (2007).
http://www.greenlandice.org/