Ocean thermal expansion and glacier mass loss, caused by the global mean temperature increases, have had the largest contributions to global mean sea level (GMSL) (Hock et al. 2009). The melting of glaciers and ice caps (excluding the glaciers surrounding Greenland and Antarctica) contributed to sea-level rise by about 0.8 mm per year from 2001–2004 (Kaser et al., 2006) and the rate of sea level rise is increasing. However, observational data is temporally limited, and satellite/airborne measurements lack resolution (Church et al., 2013). This adds error to the computing of the past ice volume lost to melting, and hence there is significant uncertainty in its current contribution to GMSL change. As a result, future predictions of 21st century GMSL also contain large uncertainty (Fig.1).
The use of the new global inventory on nearly all glaciers in the world (Arendt et al. 2012), and hence eliminating the global upscaling of glaciers, improved the quantification of uncertainty in the projections of glacier contributions to sea level change (Radic et al., 2014), but a poor understanding of some important cryospheric processes remain. Ice sheet rapid dynamic response, including complex snow hydrology and drifting snow process, are implemented as first-order approximations and are difficult to implement on a global scale (Luthi, 2009). Kangerdlussuaq and Helheim glaciers in the south-east and Jakobshavn in the south west of Greenland (Nick et al., 2009; Kerr, 2009) have rapidly thinned and retreated in recent years, possibly due to the hydraulic acceleration of the ice sheet, but it is not understood whether marine ice sheet instability (MISI) and the infiltration of surface melt water provides a dynamical effect of the movement of the ice (van de Wal et al., 2008; Shepherd et al., 2009). MISI is not currently factored into GCMs (Favier et al., 2014).
The calibration and initialisation of GCMs is affected by poor observational data, as well as by non-perfect empirical parameters. For example, the temperature-index model may not represent reality at the scale of individual glaciers. In addition, under future climate conditions the parameters may change. Emissions and climate scenarios are used to help project future climate forcings, providing several different outcomes (Fig.1), and therefore not one single scenario can be assumed. Natural forcings, such as volcanic eruptions and changes in incoming solar radiation, also add uncertainty to glacier mass changes, particularly in the lower latitudes (Huss et al., 2009).
GCMs assume a direct, instantaneous GMSL equivalent from glacier mass loss. However, the effect of meltwater flow through aquifers and basins, and the changes to the storage of water on land, is unclear. Water storage changes will result from the building of dams, the mining of groundwater, and the isostatic adjustment of land surface and ocean floor due to changes in ice and water loading.
The use of the new global inventory on nearly all glaciers in the world (Arendt et al. 2012), and hence eliminating the global upscaling of glaciers, improved the quantification of uncertainty in the projections of glacier contributions to sea level change (Radic et al., 2014), but a poor understanding of some important cryospheric processes remain. Ice sheet rapid dynamic response, including complex snow hydrology and drifting snow process, are implemented as first-order approximations and are difficult to implement on a global scale (Luthi, 2009). Kangerdlussuaq and Helheim glaciers in the south-east and Jakobshavn in the south west of Greenland (Nick et al., 2009; Kerr, 2009) have rapidly thinned and retreated in recent years, possibly due to the hydraulic acceleration of the ice sheet, but it is not understood whether marine ice sheet instability (MISI) and the infiltration of surface melt water provides a dynamical effect of the movement of the ice (van de Wal et al., 2008; Shepherd et al., 2009). MISI is not currently factored into GCMs (Favier et al., 2014).
The calibration and initialisation of GCMs is affected by poor observational data, as well as by non-perfect empirical parameters. For example, the temperature-index model may not represent reality at the scale of individual glaciers. In addition, under future climate conditions the parameters may change. Emissions and climate scenarios are used to help project future climate forcings, providing several different outcomes (Fig.1), and therefore not one single scenario can be assumed. Natural forcings, such as volcanic eruptions and changes in incoming solar radiation, also add uncertainty to glacier mass changes, particularly in the lower latitudes (Huss et al., 2009).
GCMs assume a direct, instantaneous GMSL equivalent from glacier mass loss. However, the effect of meltwater flow through aquifers and basins, and the changes to the storage of water on land, is unclear. Water storage changes will result from the building of dams, the mining of groundwater, and the isostatic adjustment of land surface and ocean floor due to changes in ice and water loading.
Figure 1. Projected glacier volume loss and corresponding GMSL equivalent over the 21st century (Radic et al. 2014).
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