Sea-Level Budget Closure_cci

2017 - 2019

Meltwater from glaciers currently contributes about one third to GMSL and is thus a key component of sea-level rise. The main problem in accurately estimating the contribution of glacier melt is related to the large number of glaciers (ca. 200,000), only a few hundred of which are annually measured in terms of their mass changes. Moreover, their representativeness for the mass changes of the surrounding larger mountain region is only known for a few regions, probably variable over time, and simple extrapolation schemes fail due to their diverse nature. Current best estimates of their global mass change thus rely on a combination of field and remote sensing-based observations. As these are temporarily restricted to the measurement period of the satellites, and as satellite-sampling is spatially incomplete as well, numerical models help to bridge the spatio-temporal coverage and extend the time periods backwards and forwards in time. Only one of these models (Marzeion et al., 2012) is able to extend time-series backwards in time while also considering glacier geometry change. All these models require three key datasets as an input to determine global glacier mass changes: (a) a globally complete dataset of glacier outlines from a known point in time, (b) a digital elevation model (DEM) to derive their area-elevation distribution, and (c) global meteorological datasets covering the intended modelling period. Moreover, independent calibration and validation datasets are required to achieve good quality and to quantify systematic and random errors. The validation of all glacier models currently under development (e.g., considering more processes, optimizing code, etc.) indicate that their limiting factor lies in the initial and boundary conditions. Major future improvements can thus be expected to be related to dataset (a), the quality of the glacier outlines in the global inventory. The only currently available global dataset of glacier outlines is the Randolph Glacier Inventory (RGI), which has been compiled in an ad-hoc community effort for IPCC AR5. It still contains regional shortcomings in quality (e.g. seasonal snow mapped as glaciers), but it is constantly being improved by the community as well as the Glaciers_cci project. This project will focus on two key components to further improve upon current best estimates regarding the sea-level contribution of glacier melt: (i) improvements of the model used to determine a global value, mostly based on re-calibration using additional observational data, and (ii) improvements of the quality and consistency (in a temporal sense) of the glacier inventory used for initialization.

Funding Agency: 
European Space Agency
Funding Amount: 
€70 000