2023

1. HESS

   A snow and glacier hydrological model for large catchments – case study for the Naryn River, Central Asia

   Shannon, S. R., Payne, A., Freer, J., Coxon, G., Kauzlaric, M., Kriegel, D., and Harrison, S.

   Hydrology and Earth System Sciences 2023

   Abs HTML PDF

   In this paper we implement a degree day snow and glacier melt model into the Dynamic fluxEs and ConnectIvity for Predictions of HydRology (DECIPHeR) model. The purpose is to develop a hydrological model that can be applied to large glaciated and snow-fed catchments, yet is computationally efficient enough to include model uncertainty in streamflow predictions. The model is evaluated by simulating monthly discharge at six gauging stations in the Naryn River catchment (57,833 km2) in Central Asia over the period 1951 to a variable end date between 1980 and 1995 depending on the availability of discharge observations. The spatial distribution of simulated snow cover is validated against MODIS weekly snow extent for the years 2001–2007. Discharge is calibrated by selecting parameter sets using Latin Hypercube sampling and assessing the model performance using six evaluation metrics.The model shows good performance at simulating monthly discharge for the evaluation period (NSE is 0.74 < NSE < 0.87) and validation period (0.7 < NSE < 0.9) where the range of NSE values represent the 5th–95th percentile prediction limits across the gauging stations. The exception is the Uch-Kurgan station which exhibits a reduction in model performance during the validation period attributed to commissioning of the Toktugal reservoir in 1975 which impacted the observations. The model reproduces the spatial extent in seasonal snow cover well, capturing 86 % of the snow extent on average (2001–2007) for the median ensemble member of the best 0.5 % evaluation simulations, when evaluated against MODIS snow extent.We establish the present-day contributions of glacier melt, snow melt and rainfall to the total annual discharge and the timing of when these components dominate river flow. The model predicts the observed increase in discharge during the spring (April–May) associated with the onset of snow melting and peak discharge during the summer (June, July and August) associated with glacier melting well. At all stations snow melting is the largest component, followed by the rainfall and the glacier melt component. In August, glacier melting can contribute up to 66 % of the total discharge at the highly glacierised Naryn headwater sub-catchment. The glaciated area predicted by the best 0.5 % evaluation simulations overlap the Landsat observations for the late 1990s and mid-2000s. Despite good predictions for discharge, the model produces a large range of estimates for the glaciated area (680 km2–1,196 km2) (5th–95th percentile limits) at the end of the simulation period. To constrain these estimates further, additional observations such as glacier mass balance, snow depth or snow extent should be used directly to constrain model simulations.

2022

1. Glob Plan Change

   160 glacial lake outburst floods (GLOFs) across the Tropical Andes since the Little Ice Age

   Emmer, Adam, Wood, Joanne L., Cook, Simon J., Harrison, Stephan, Wilson, Ryan, Diaz-Moreno, Alejandro, Reynolds, John M., Torres, Juan C., Yarleque, Christian, Mergili, Martin, Jara, Harrinson W., Bennett, Georgie, Caballero, Adriana, Glasser, Neil F., Melgarejo, Enver, Riveros, Christian, Shannon, Sarah, Turpo, Efrain, Tinoco, Tito, Torres, Lucas, Garay, David, Villafane, Hilbert, Garrido, Henrry, Martinez, Carlos, Apaza, Nebenka, Araujo, Julia, and Poma, Carlos

   Global and Planetary Change 2022

   Abs HTML PDF

   Assessing the extent to which glacial lake outburst floods (GLOFs) are increasing in frequency in modern times and whether their incidence is driven by anthropogenic climate change requires historical context. However, progress on this issue is hampered by incomplete GLOF inventories, especially in remote mountain regions. Here, we exploit high-resolution, multi-temporal satellite and aerial imagery, and documentary data to identify GLOF events across the glacierized Cordilleras of Peru and Bolivia, using a set of diagnostic geomorphic features. A total of 160 GLOFs from 151 individual sites are characterised and analysed, tripling the number of previously reported events. We provide statistics on location, magnitude, timing and characteristics of these events with implications for regional GLOF hazard identification and assessment. Furthermore, we describe several cases in detail and document a wide range of process chains associated with Andean GLOFs.

2021

1. Nature

   Projected land ice contributions to twenty-first-century sea level rise

   Edwards, T. L., Nowicki, S., Marzeion, B., Hock, R., Goelzer, ..., Shannon, S., Smith, R. S., Straneo, F., Sun, S. N., Tarasov, L., Trusel, L. D., Van Breedam, J., Wal, R., Broeke, M., Winkelmann, R., Zekollari, H., Zhao, C., Zhang, T., and Zwinger, T.

   2021

   Abs HTML PDF

   The land ice contribution to global mean sea level rise has not yet been predicted1 using ice sheet and glacier models for the latest set of socio-economic scenarios, nor using coordinated exploration of uncertainties arising from the various computer models involved. Two recent international projects generated a large suite of projections using multiple models but primarily used previous-generation scenarios and climate models, and could not fully explore known uncertainties. Here we estimate probability distributions for these projections under the new scenarios using statistical emulation of the ice sheet and glacier models. We find that limiting global warming to 1.5 degrees Celsius would halve the land ice contribution to twenty-first-century sea level rise, relative to current emissions pledges. The median decreases from 25 to 13 centimetres sea level equivalent (SLE) by 2100, with glaciers responsible for half the sea level contribution. The projected Antarctic contribution does not show a clear response to the emissions scenario, owing to uncertainties in the competing processes of increasing ice loss and snowfall accumulation in a warming climate. However, under risk-averse (pessimistic) assumptions, Antarctic ice loss could be five times higher, increasing the median land ice contribution to 42 centimetres SLE under current policies and pledges, with the 95th percentile projection exceeding half a metre even under 1.5 degrees Celsius warming. This would severely limit the possibility of mitigating future coastal flooding. Given this large range (between 13 centimetres SLE using the main projections under 1.5 degrees Celsius warming and 42 centimetres SLE using risk-averse projections under current pledges), adaptation planning for twenty-first-century sea level rise must account for a factor-of-three uncertainty in the land ice contribution until climate policies and the Antarctic response are further constrained.

2. GEOGR ANN A

   Is ice in the Himalayas more resilient to climate change than we thought?

   Harrison, S., Jones, D., Anderson, K., Shannon, S., and Betts, R. A.

   2021

   Abs HTML PDF

   In the Himalaya, climate change threatens mountain water resources as glaciers melt and changes in runoff and water availability are likely to have considerable negative impacts on ecological and human systems. While much has been written on the effect of climate change on glaciers in the Himalaya and its impact on sustainability, almost nothing has been published on rock glaciers in the region and their role in maintaining water supplies as the climate warms. Rock glaciers are important components of the Himalayan hydrological system because they are present in almost all regions of the Himalaya and are climatically more resilient than other glacier types owing to an insulating layer of debris cover. Research from other mountain regions shows that they contain potentially important water stores, although in the Himalaya, there is almost no information on their number, spatial distribution and response to future climate change. The extent to which this contributes to higher resilience of the Himalayan cryosphere as a whole is still an open question. This paper argues that research into Himalayan rock glaciers that reveals their hydrological significance is critical for underpinning climate change adaptation strategies and to ensure that this highly populated region is in a strong position to meet sustainable development goals.

3. Sci. Total Environ.

   Rock glaciers represent hidden water stores in the Himalaya

   Jones, D. B., Harrison, S., Anderson, K., Shannon, S., and Betts, R. A.

   2021

   Abs HTML PDF

   In the high mountains of Asia, ongoing glacier retreat threatens human and ecological systems through reduced water availability. Rock glaciers are climatically more resistant than glaciers and contain valuable water volume equivalents (WVEQ). Across High Mountain Asia (HMA) the WVEQ of rock glaciers is poorly quantified, and thus their hydrological significance versus glaciers is unknown. Here we present the first systematic assessment of Himalayan rock glaciers, totalling  25,000 landforms with an areal coverage of  3747 km2. We calculate the WVEQ of Himalayan rock glaciers to be 51.80 ± 10.36 km3. Their comparative importance versus glaciers (rock glacier: glacier WVEQ ratio) is 1:25, which means that they constitute hydrologically valuable long-term water stores. In the context of climate-driven glacier recession, their relative hydrological value will likely increase. These cryospheric stores should be included in future scenario modelling to understand their role in sustainable water management for HMA.

4. Glob Plan Change

   Contemporary glacial lakes in the Peruvian Andes

   Wood, J.L., Harrison, S., Wilson, R., Emmer, A., Yarleque, C., Glasser, N.F., Torres, J.C., Caballero, A., Araujo, J., Bennett, G.L., Diaz-Moreno, A., Garay, D., Jara, H., Poma, C., Reynolds, J.M., Riveros, C.A., Romero, E., Shannon, S., Tinoco, T., Turpo, E., and Villafane, H.

   Global and Planetary Change 2021

   Abs HTML PDF

   Glacier recession in response to climate warming has resulted in an increase in the size and number of glacial lakes. Glacial lakes are an important focus for research as they impact water resources, glacier mass balance, and some produce catastrophic glacial lake outburst floods (GLOFs). Glaciers in Peru have retreated and thinned in recent decades, prompting the need for monitoring of ice- and water-bodies across the cordilleras. These monitoring efforts have been greatly facilitated by the availability of satellite imagery. However, knowledge gaps remain, particularly in relation to the formation, temporal evolution, and catastrophic drainage of glacial lakes. In this paper we address this gap by producing the most current and detailed glacial lake inventory in Peru and provide a set of reproducible methods that can be applied consistently for different time periods, and for other mountainous regions. The new lake inventory presented includes a total of 4557 glacial lakes covering a total area of 328.85 km2. In addition to detailing lake distribution and extent, the inventory includes other metrics, such as dam type and volume, which are important for GLOF hazard assessments. Analysis of these metrics showed that the majority of glacial lakes are detached from current glaciers (97%) and are classified as either embedded (i.e. bedrock dammed;  64% of all lakes) or (moraine) dammed ( 28% of all lakes) lakes. We also found that lake size varies with dam type; with dammed lakes tending to have larger areas than embedded lakes. The inventory presented provides an unparalleled view of the current state of glacial lakes in Peru and represents an important first step towards (1) improved understanding of glacial lakes and their topographic and morphological characteristics and (2) assessing risk associated with GLOFs.

2020

1. Earths Future

   Partitioning the Uncertainty of Ensemble Projections of Global Glacier Mass Change

   Marzeion, B., Hock, R., Anderson, B., Bliss, A., Champollion, N., Fujita, K., Huss, M., Immerzeel, W. W., Kraaijenbrink, P., Malles, J. H., Maussion, F., Radic, V., Rounce, D. R., Sakai, A., Shannon, S., Wal, R., and Zekollari, H.

   2020

   Abs HTML PDF

   Glacier mass loss is recognized as a major contributor to current sea level rise. However, large uncertainties remain in projections of glacier mass loss on global and regional scales. We present an ensemble of 288 glacier mass and area change projections for the 21st century based on 11 glacier models using up to 10 general circulation models and four Representative Concentration Pathways (RCPs) as boundary conditions. We partition the total uncertainty into the individual contributions caused by glacier models, general circulation models, RCPs, and natural variability. We find that emission scenario uncertainty is growing throughout the 21st century and is the largest source of uncertainty by 2100. The relative importance of glacier model uncertainty decreases over time, but it is the greatest source of uncertainty until the middle of this century. The projection uncertainty associated with natural variability is small on the global scale but can be large on regional scales. The projected global mass loss by 2100 relative to 2015 (79 +/- 56 mm sea level equivalent for RCP2.6, 159 +/- 86 mm sea level equivalent for RCP8.5) is lower than, but well within, the uncertainty range of previous projections.

2. Himalayan Weather and Climate and their Impact on the Environment. Impacts of Climate Change on Himalayan Glaciers: Processes, Predictions and Uncertainties

   L., Parry, S., Harrison, R., Betts, S., Shannon, D.B., Jones, and J., Knight

   2020

   Abs HTML PDF

   The glaciers of the Hindu Kush Himalaya region (HKH) produce the water for around 40% of the world’s population. Over the past century these glaciers have lost mass in response to recent climate change and they are predicted to lose more in the future. The precise ways in which glaciers will respond to future climate change are still unknown; many will melt entirely, but some will undergo a transi- tion to debris-covered glaciers which will retard melting, and others will undergo a further transition to form rock glaciers whose response to atmospheric warming and changes in precipitation is as yet unclear. As a result, this chapter stresses the para- glacial response of mountain systems to deglaciation to better understand future glacier recession in the region.

2019

1. Climatic Change

   Uncertainty in geomorphological responses to climate change

   Harrison, S., Mighall, T., Stainforth, D. A., Allen, P., Macklin, M., Anderson, E., Knight, J., Mauquoy, D., Passmore, D., Rea, B., Spagnolo, M., and Shannon, S.

   2019

   Abs HTML PDF

   Successful adaptation to climate change at regional scales can often depend on understanding the nature of geomorphological responses to climate change at those scales. Here we use evidence from landscapes which are known to be environmentally sensitive to show that geomorphological change in response to shifts in climate can be highly nonlinear. Our study sites are two mountain massifs on the western coast of Ireland. Both sites have similar geological and Pleistocene glacial histories and are similar topographically, geomorphologically and in their climate histories. We show that despite these similarities their response to late Holocene, climate change has differed. Both massifs have responded to short-term climate changes over the last 4500 years that are considered to have been uniform across the region, but these climate changes have resulted in highly differentiated and nonlinear landscape responses. We argue this reflects nonlinearity in the forcing-response processes at such scales and suggests that current approaches to modelling the response of such systems to future climate change using numerical climate models may not accurately capture the landscape response. We end by discussing some of the implications for obtaining decision-relevant predictions of landscape responses to climatic forcing and for climate change adaptation and planning, using regional climate models.

2. Cryosphere

   Global glacier volume projections under high-end climate change scenarios

   Shannon, S., Smith, R., Wiltshire, A., Payne, T., Huss, M., Betts, R., Caesar, J., Koutroulis, A., Jones, D., and Harrison, S.

   2019

   Abs HTML PDF

   The Paris agreement aims to hold global warming to well below 2 degrees C and to pursue efforts to limit it to 1.5 degrees C relative to the pre-industrial period. Recent estimates based on population growth and intended carbon emissions from participant countries suggest global warming may exceed this ambitious target. Here we present glacier volume projections for the end of this century, under a range of high-end climate change scenarios, defined as exceeding +2 degrees C global average warming relative to the pre-industrial period. Glacier volume is modelled by developing an elevation-dependent mass balance model for the Joint UK Land Environment Simulator (JULES). To do this, we modify JULES to include glaciated and unglaciated surfaces that can exist at multiple heights within a single grid box. Present-day mass balance is calibrated by tuning albedo, wind speed, precipitation, and temperature lapse rates to obtain the best agreement with observed mass balance profiles. JULES is forced with an ensemble of six Coupled Model Intercomparison Project Phase 5 (CMIP5) models, which were downscaled using the high-resolution HadGEM3-A atmosphere-only global climate model. The CMIP5 models use the RCP8.5 climate change scenario and were selected on the criteria of passing +2 degrees C global average warming during this century. The ensemble mean volume loss at the end of the century plus or minus 1 standard deviation is -64 +/- 5% for all glaciers excluding those on the peripheral of the Antarctic ice sheet. The uncertainty in the multi-model mean is rather small and caused by the sensitivity of HadGEM3-A to the boundary conditions supplied by the CMIP5 models. The regions which lose more than 75% of their initial volume by the end of the century are Alaska, western Canada and the US, Iceland, Scandinavia, the Russian Arctic, central Europe, Caucasus, high-mountain Asia, low latitudes, southern Andes, and New Zealand. The ensemble mean ice loss expressed in sea level equivalent contribution is 215.2 +/- 21.3 mm. The largest contributors to sea level rise are Alaska (44.6 +/- 1.1 mm), Arctic Canada north and south (34.9 +/- 3.0 mm), the Russian Arctic (33.3 +/- 4.8 mm), Greenland (20.1 +/- 4.4), high-mountain Asia (combined central Asia, South Asia east and west), (18.0 +/- 0.8 mm), southern Andes (14.4 +/- 0.1 mm), and Svalbard (17.0 +/- 4.6 mm). Including parametric uncertainty in the calibrated mass balance parameters gives an upper bound global volume loss of 281.1mm of sea level equivalent by the end of the century. Such large ice losses will have inevitable consequences for sea level rise and for water supply in glacier-fed river systems.

3. Geomorphology

   The 2015 Chileno Valley glacial lake outburst flood, Patagonia

   Wilson, R., Harrison, S., Reynolds, J., Hubbard, A., Glasser, N. F., Wundrich, O., Anacona, P. I., Mao, L., and Shannon, S.

   2019

   Abs HTML PDF

   Glacial Lake Outburst Floods (GLOFs) have become increasingly common over the past century in response to climate change, posing risks for human activities in many mountain regions. In this paper we document and reconstruct the sequence of events and impact of a large GLOF that took place in December 2015 in the Chileno Valley, Patagonia. Hydrograph data suggests that the flood continued for around eight days with an estimated total discharge of 105.6 x 10(6) m(3) of water. The sequence of events was as follows: (1) A large debris flow entered the lake from two steep and largely non-vegetated mountain gullies located northeast of the Chileno Glacier terminus. (2) Water displaced in the lake by the debris flow increased the discharge through the Chileno Lake outflow. (3) Lake and moraine sediments were eroded by the flood. (4) Eroded sediments were redistributed downstream by the GLOF. The post-GLOF channel at the lake outlet widened in some places by >130 m and the surface elevation of the terrain lowered by a maximum of 38.8 +/- 1.5 m. Farther downstream, large amounts of entrained sediment were deposited at the head of an alluvial plain and these sediments produced an similar to 340 m wide fan with an average increase in surface elevation over the pre-GLOF surface of 4.6 +/- 1.5 m. We estimate that around 3.5 million m(3) of material was eroded from the flood-affected area whilst over 0.5 million m(3) of material was deposited in the downstream GLOF fan. The large debris flow that triggered the GLOF was probably a paraglacial response to glacier recession from its Little Ice Age limits. We suggest that GLOFs will continue to occur in these settings in the future as glaciers further recede in response to global warming and produce potentially unstable lakes. Detailed studies of GLOF events are currently limited in Patagonia and the information presented here will therefore help to inform future glacial hazard assessments in this region. (C) 2019 The Author(s). Published by Elsevier B.V.

2018

1. Glob Plan Change

   Glacial lakes of the Central and Patagonian Andes

   Wilson, R., Glasser, N. F., Reynolds, J. M., Harrison, S., Anacona, P. I., Schaefer, M., and Shannon, S.

   2018

   Abs HTML PDF

   The prevalence and increased frequency of high-magnitude Glacial Lake Outburst Floods (GLOFs) in the Chilean and Argentinean Andes suggests this region will be prone to similar events in the future as glaciers continue to retreat and thin under a warming climate. Despite this situation, monitoring of glacial lake development in this region has been limited, with past investigations only covering relatively small regions of Patagonia. This study presents new glacial lake inventories for 1986, 2000 and 2016, covering the Central Andes, Northern Patagonia and Southern Patagonia. Our aim was to characterise the physical attributes, spatial distribution and temporal development of glacial lakes in these three sub-regions using Landsat satellite imagery and image datasets available in Google Earth and Bing Maps. Glacial lake water volume was also estimated using an empirical area-volume scaling approach. Results reveal that glacial lakes across the study area have increased in number (43%) and areal extent (7%) between 1986 and 2016. Such changes equate to a glacial lake water volume increase of 65 km3 during the 30-year observation period. However, glacial lake growth and emergence was shown to vary sub-regionally according to localised topography, meteorology, climate change, rate of glacier change and the availability of low gradient ice areas. These and other factors are likely to influence the occurrence of GLOFs in the future. This analysis represents the first large-scale census of glacial lakes in Chile and Argentina and will allow for a better understanding of lake development in this region, as well as, providing a basis for future GLOF risk assessments.

2015

1. Cryosphere

   Century-scale simulations of the response of the West Antarctic Ice Sheet to a warming climate

   Cornford, S. L., Martin, D. F., Payne, A. J., Ng, E. G., Le Brocq, A. M., Gladstone, R. M., Edwards, T. L., Shannon, S. R., Agosta, C., Broeke, M. R., Hellmer, H. H., Krinner, G., Ligtenberg, S. R. M., Timmermann, R., and Vaughan, D. G.

   2015

   Abs Bib PDF

   We use the BISICLES adaptive mesh ice sheet model to carry out one, two, and three century simulations of the fast-flowing ice streams of the West Antarctic Ice Sheet, deploying sub-kilometer resolution around the grounding line since coarser resolution results in substantial underestimation of the response. Each of the simulations begins with a geometry and velocity close to present-day observations, and evolves according to variation in meteoric ice accumulation rates and oceanic ice shelf melt rates. Future changes in accumulation and melt rates range from no change, through anomalies computed by atmosphere and ocean models driven by the El and A1B emissions scenarios, to spatially uniform melt rate anomalies that remove most of the ice shelves over a few centuries. We find that variation in the resulting ice dynamics is dominated by the choice of initial conditions and ice shelf melt rate and mesh resolution, although ice accumulation affects the net change in volume above flotation to a similar degree. Given sufficient melt rates, we compute grounding line retreat over hundreds of kilometers in every major ice stream, but the ocean models do not predict such melt rates outside of the Amundsen Sea Embayment until after 2100. Within the Amundsen Sea Embayment the largest single source of variability is the onset of sustained retreat in Thwaites Glacier, which can triple the rate of eustatic sea level rise.

   @article{RN224,
     bibtex_show = {true},
     author = {Cornford, S. L. and Martin, D. F. and Payne, A. J. and Ng, E. G. and Le Brocq, A. M. and Gladstone, R. M. and Edwards, T. L. and Shannon, S. R. and Agosta, C. and van den Broeke, M. R. and Hellmer, H. H. and Krinner, G. and Ligtenberg, S. R. M. and Timmermann, R. and Vaughan, D. G.},
     title = {Century-scale simulations of the response of the West Antarctic Ice Sheet to a warming climate},
     journal = {Cryosphere},
     volume = {9},
     number = {4},
     pages = {1579-1600},
     issn = {1994-0416},
     doi = {10.5194/tc-9-1579-2015},
     url = {<Go to ISI>://WOS:000360661700017},
     year = {2015},
     abbr = {Cryosphere},
     pdf = {cornford.pdf},
     type = {Journal Article}
   }

2013

1. J. of Glaciology

   Sensitivity of Greenland ice sheet projections to model formulations

   Goelzer, H., Huybrechts, P., Furst, J. J., Nick, F. M., Andersen, M. L., Edwards, T. L., Fettweis, X., Payne, A. J., and Shannon, S.

   2013

   Abs HTML PDF

   Physically based projections of the Greenland ice sheet contribution to future sea-level change are subject to uncertainties of the atmospheric and oceanic climatic forcing and to the formulations within the ice flow model itself. Here a higher-order, three-dimensional thermomechanical ice flow model is used, initialized to the present-day geometry. The forcing comes from a high-resolution regional climate model and from a flowline model applied to four individual marine-terminated glaciers, and results are subsequently extended to the entire ice sheet. The experiments span the next 200 years and consider climate scenario SRES A1B. The surface mass-balance (SMB) scheme is taken either from a regional climate model or from a positive-degree-day (PDD) model using temperature and precipitation anomalies from the underlying climate models. Our model results show that outlet glacier dynamics only account for 6-18% of the sea-level contribution after 200 years, confirming earlier findings that stress the dominant effect of SMB changes. Furthermore, interaction between SMB and ice discharge limits the importance of outlet glacier dynamics with increasing atmospheric forcing. Forcing from the regional climate model produces a 14-31% higher sea-level contribution compared to a PDD model run with the same parameters as for IPCC AR4.

2. PNAS

   Enhanced basal lubrication and the contribution of the Greenland ice sheet to future sea-level rise

   Shannon, Sarah R., Payne, Antony J., Bartholomew, Ian D., Broeke, Michiel R., Edwards, Tamsin L., Fettweis, Xavier, Gagliardini, Olivier, Gillet-Chaulet, Fabien, Goelzer, Heiko, Hoffman, Matthew J., Huybrechts, Philippe, Mair, Douglas W. F., Nienow, Peter W., Perego, Mauro, Price, Stephen F., Smeets, C. J. P. Paul, Sole, Andrew J., Wal, Roderik S. W., and Zwinger, Thomas

   2013

   Abs HTML PDF

   We assess the effect of enhanced basal sliding on the flow and mass budget of the Greenland ice sheet, using a newly developed parameterization of the relation between meltwater runoff and ice flow. A wide range of observations suggest that water generated by melt at the surface of the ice sheet reaches its bed by both fracture and drainage through moulins. Once at the bed, this water is likely to affect lubrication, although current observations are insufficient to determine whether changes in subglacial hydraulics will limit the potential for the speedup of flow. An uncertainty analysis based on our best-fit parameterization admits both possibilities: continuously increasing or bounded lubrication. We apply the parameterization to four higher-order ice-sheet models in a series of experiments forced by changes in both lubrication and surface mass budget and determine the additional mass loss brought about by lubrication in comparison with experiments forced only by changes in surface mass balance. We use forcing from a regional climate model, itself forced by output from the European Centre Hamburg Model (ECHAM5) global climate model run under scenario A1B. Although changes in lubrication generate widespread effects on the flow and form of the ice sheet, they do not affect substantial net mass loss; increase in the ice sheet’s contribution to sea-level rise from basal lubrication is projected by all models to be no more than 5% of the contribution from surface mass budget forcing alone.

2012

1. Cryosphere

   Greenland ice sheet surface mass balance: evaluating simulations and making projections with regional climate models

   Rae, J. G. L., Aoalgeirsdottir, G., Edwards, T. L., Fettweis, X., Gregory, J. M., Hewitt, H. T., Lowe, J. A., Lucas-Picher, P., Mottram, R. H., Payne, A. J., Ridley, J. K., Shannon, S. R., Berg, W. J., Wal, R. S. W., and Broeke, M. R.

   2012

   Abs HTML PDF

   Four high-resolution regional climate models (RCMs) have been set up for the area of Greenland, with the aim of providing future projections of Greenland ice sheet surface mass balance (SMB), and its contribution to sea level rise, with greater accuracy than is possible from coarser-resolution general circulation models (GCMs). This is the first time an intercomparison has been carried out of RCM results for Greenland climate and SMB. Output from RCM simulations for the recent past with the four RCMs is evaluated against available observations. The evaluation highlights the importance of using a detailed snow physics scheme, especially regarding the representations of albedo and meltwater refreezing. Simulations with three of the RCMs for the 21st century using SRES scenario A1B from two GCMs produce trends of between −5.5 and −1.1 Gt yr−2 in SMB (equivalent to +0.015 and +0.003 mm sea level equivalent yr−2), with trends of smaller magnitude for scenario E1, in which emissions are mitigated. Results from one of the RCMs whose present-day simulation is most realistic indicate that an annual mean near-surface air temperature increase over Greenland of   2°C would be required for the mass loss to increase such that it exceeds accumulation, thereby causing the SMB to become negative, which has been suggested as a threshold beyond which the ice sheet would eventually be eliminated.

2011

1. GMD

   A new dust cycle model with dynamic vegetation: LPJ-dust version 1.0

   Shannon, S., and Lunt, D. J.

   2011

   Abs HTML PDF

   This paper presents a new offline dust cycle model which uses the Lund-Potsdam-Jena dynamic global vegetation model (Sitch et al., 2003) to calculate time varying dust sources. Surface emissions are calculated by simulating the processes of saltation and sandblasting using an existing model. Dust particles are transported using the TOMCAT chemical transport model. Dust particles are removed from the atmosphere by dry deposition and sub-cloud scavenging. The model is designed so that it can be driven using reanalysis data or GCM derived fields. To improve the performance of the model, threshold values for vegetation cover, soil moisture, snow depth and threshold friction velocity, used to determine surface emissions are tuned. The effectiveness of three sub-cloud scavenging schemes are also tested. An ensemble of tuning experiments are evaluated against dust deposition and surface concentration measurements. Surface emissions which produce the best agreement with observations range from 1600 to 2400 Mtyr(-1).

2009

1. Thesis

   Modelling the atmospheric mineral dust cycle using a dynamic global vegetation model

   Shannon, S.

   2009

   PDF