Ice melting and sea level rise

So far, we have talked about ice melting from sea ice, glaciers and ice sheets, and have mentioned some serious impacts. This time, we are going to systematically look at one significant global issue derived from ice melting, i.e. sea level rising. Will the world be submerged in the future?



Figure 1. Processes relevant to sea level change in IPCC. (Source: IPCC, 2013)

There are three factors contribute to sea level rise, including thermal expansion, added water from land ice (glaciers and ice sheets) and change in basin depth. Thermal expansion is the biggest contributor to sea level rise (IPCC, 2013), and the topographic change currently contribute to 3 mm/yr drop in sea level due to glacial isostatic adjustment. I will only discuss the contribution from ice melting below, which is sea level change from changes in mass of ocean. The unit is sea level equivalent (SLE), mentioned in previous posts, i.e. sea level equivalent to a mass of water (mass divided by density (1000kg/m³) and area (362500 billion m²) Approximately, adding 362.5 Gt water will lead to 1 mm rise in sea level. Figure 1 shows how IPCC AR5 assessed the processes involving in modelling sea level change, and the linkage between the relevant sections. Sea level change can be modelled via several types of model, while Atmosphere-Ocean General Circulation Models (AOGCMs) provide most comprehensive simulations. Regional Climate Models (RCMs) with information form AOGCMs are important to simulating changes in glaciers and ice sheets.

Ice losses from glaciers and ice sheets have been mentioned in early posts (the first and the last three posts) with unit in Gt. Convert them to SLE:

• Total ice loss from glaciers in SLE was 0.62 ± 0.37 mm/yr during 1971-2009, 0.76 ± 0.37 mm/yr during 1993-2007, and 0.83 ± 0.37 mm/yr during 2005-2009;
• During 1992-2001, ice loss was -0.02 to 0.20 mm/yr from Greenland ice sheet and -0.10 to 0.27 mm/yr form Antarctica ice sheet, and during 2002-2011 the rate was 0.43-0.76 mm/yr from Greenland and 0.20-0.61 mm/yr from Antarctica.

Figure 2 shows the contribution to sea level change up to 2100 under different scenarios. Major contribution would come from ice melting from glaciers, contributing to 0.08-0.38 m rise by the end of this century, while 0.10-0.19 m mean rise under 4 RCPs (IPCC, 2013) . Based on modelled future projections, Greenland ice sheet would contribute to a rise below 0.11 m, while Antarctica ice sheet would likely to drop sea level with predicted increase in precipitation, according to IPCC (2013).

Figure 2. Future projections of sea level rise under 4 RCPs. (Source: IPCC, 2013)