Sarah Raper, Understanding Sea-level Rise and Variability, 6-9 June, 2006 Paris Glacier modeling: Current Status and Needed Improvements Sarah Raper Centre for Air Transport and the Environment Manchester Metropolitan University

Sarah Raper, Understanding Sea-level Rise and Variability, 6-9 June, 2006 Paris Schematic diagram illustrating the cascade of uncertainties in modelling the contribution to SLR from glaciers and ice caps climate and climate change glacier area size distribution downscale climate change hypsometry mass balance change in volume change in sea level ice dynamics climate

Sarah Raper, Understanding Sea-level Rise and Variability, 6-9 June, 2006 Paris Location of glaciers and icecaps glaciers in Greenland and Antarctica are problematic Estimates often exclude these for the following reasons: ice-sheet retreat under global warming will result in ice masses becoming separated from the ice-sheets, thus increasing the ice volume in the glacier and ice cap category. inventory data for these regions is poor or non-existent. it is not clear where the ice sheets end and the glaciers begin in for instance the Antarctic Peninsula. From Braithwaite and Raper, 2002

Sarah Raper, Understanding Sea-level Rise and Variability, 6-9 June, 2006 Paris adapted from Raper and Braithwaite, 2005 Area and Volume size distribution Volume estimates in sea level equivalent Outside Greenland and Antarctica: 0.15m Ohmura (2004) 0.24 (0.26)m Raper and Braithwaite (2005) 0.37 m Dyurgerov and Meier (2005) Greenland and Antarctica (excluding ice-sheets): 0.34 m Dyurgerov and Meier (2005) Need to make the addition of the largest glaciers to the glacier inventory a priority.

Sarah Raper, Understanding Sea-level Rise and Variability, 6-9 June, 2006 Paris Uncertainty in ice volume from the previous slide is about  45%, leading to uncertainty in glacier and icecap contribution to 21 st C SLR ~ 0% ±4% Mass balance

Observationally based global estimate of mass balance period mm SLE a  0.26 Consensus estimate based on Ohmura (2004), Cogley (2005), Dyurgerov and Meier (2005) The above includes glaciers and ice caps in Greenland and Antarctica.

Uncertainty in global mass balance from the previous slide is about  75%, leading to a major uncertainty in glacier and icecap contribution to 20 th C SLR Sarah Raper, Understanding Sea-level Rise and Variability, 6-9 June, 2006 Paris ±1%±9%

Sarah Raper, Understanding Sea-level Rise and Variability, 6-9 June, 2006 Paris Mass Balance Modeling concerned with the interaction of the climate with the glacier surface energy balance models reviewed in Hock (2005) degree-day models (temperature-index models) reviewed in Hock (2003) Challenge for SLR is to interpolate mass balance model results to give estimates of time evolution of mass balance over all glaciers and icecaps. physically based require detailed input data more suitable for high resolution in space and time. empirically based main inputs temperature and precipitation are readily available in gridded form from AOGCMs.

supplied by Braithwaite Sarah Raper, Understanding Sea-level Rise and Variability, 6-9 June, 2006 Paris Mass balance sensitivity is the change in mass balance for a 1 o C warming Compared here are changes for a maritime glacier (warm-wet) and a continental glacier (dry-cold) Fit mass balance model to glacier Increase temperature by 1 o C ELA

Sarah Raper, Understanding Sea-level Rise and Variability, 6-9 June, 2006 Paris From Braithwaite and Raper, 2002 methodological problem: using this method all the ice would eventually melt for any warming Mass balance sensitivity can be estimated from precipitation most glacier and ice cap projections for SLR are based on mass balance sensitivity (Gregory and Oerlemans 1998) it is necessary to scale down the glacier area as the volume decreases (van de Wal and Wild, 2001)

Mass balance sensitivity is the change in mass balance for a 1 o C warming Sarah Raper, Understanding Sea-level Rise and Variability, 6-9 June, 2006 Paris to get the mass balance sensitivity we need to integrate over the area altitude distribution (hypsometry)

Sarah Raper, Understanding Sea-level Rise and Variability, 6-9 June, 2006 Paris From Raper and Braithwaite, 2006 An alternative is to extrapolate the mass balance gradients to all glacier regions mass balance model fitted for grid points in seven regions with good data regress the resulting balance gradients on monthly temperature and precipitation climatology

Sarah Raper, Understanding Sea-level Rise and Variability, 6-9 June, 2006 Paris Uncertainty in mass balance gradients leads to uncertainty in glacier and icecap contribution to SLR in 21 st C ±2%±6%

Sarah Raper, Understanding Sea-level Rise and Variability, 6-9 June, 2006 Paris Hierarchy of ice dynamic models: 3-D models as in Schneeberger et al. (2003) 2-D models as in Oerlemans et al. (1998) Simple geometric model as in Raper and Braithwaite (2006) Ice dynamic modelling is concerned with the response of the ice geometry and hence changes in the ice exposure to climate. glacier ice-cap colder warmer Schematic of glacier and ice-cap shrinkage

Sarah Raper, Understanding Sea-level Rise and Variability, 6-9 June, 2006 Paris From Oerlemans et al, 1998 Vavilov Ice Cap Pioneer Ice Cap 0.02 K/a From Bassford et al Using coupled mass balance and ice flow models, the response of several glaciers in different climate settings under global warming is compared We can use these results to verify simpler models applied to all glaciers

Sarah Raper, Understanding Sea-level Rise and Variability, 6-9 June, 2006 Paris * single area estimate Summary uncertainties in climate forcing at glacier surface assumed that all melt finds its way directly into the oceans. none of the models discussed above account for the effect of basal sliding and ice calving simplified geometric models with implicit ice dynamics need further testing and verifying through parallel runs with more complex models