Keeping with the topic of ice melt and global sea level rise; a study by Radic & Hock (2011) looks to determine the potential contribution of mountain glaciers to sea level rise. The authors modelled the predicted mass loss of mountain glaciers globally, and from that calculated the impact that this melting could make.
The study, which looked at 40 percent of the world mountain glacier total, was the most comprehensive to date. Unlike the previous Intergovernmental Panel on Climate Change (IPCC) study which conducted the same modelling on much fewer sample sites, Radic & Hock (2011) based their study on 120,299 mountain glacier and 1,638 ice caps. Despite these differences however, the prediction that the majority of small mountain glaciers will have disappeared by the year 2100 is shared by both this study and that done by the IPCC. The paper also shows that by 2100, the melting of mountain glaciers will contribute an equivalent amount to global sea level as the Greenland and Antarctic ice sheets. Evidently then, the concern over rising global sea levels should not just be confined to the large polar ice sheets, when the potential future impact of smaller glacier melting is just as great.
Figure 1. Regional glacier volume predictions for the 21st Century.
Using ten different global climate models to predict the volume changes of the glaciers, the study found that approximately 50 percent of the glaciers with the smallest surface area (< 5 km) will have gone. The method of future volume prediction is described below:
“To quantify future volume changes, we run the calibrated mass balance model ...with downscaled monthly twenty-first-century temperature and precipitation from ten GCMs, based on the widely used mid-range greenhouse emission scenario A1B. As glaciers lose mass owing to temperature increase, they retreat and hence their hypsometry changes. We use volume-area-length scaling to account for these changes and their feedbacks to glacier mass balance ... allowing receding glaciers to approach a new equilibrium in a warming climate.”
Evidently, as discussed many times in this blog, the potential impacts on people around the world could be huge. Particularly in developing countries, the reliance on glacial meltwater for drinking water and irrigation in agriculture can be massive. Looking beyond these regional impacts of glacier shrinking or disappearance, the ten climate models predicted that on average, the small glaciers and ice caps will themselves raise the global sea level approximately 12 cm by 2100. Across all of the models, the contribution of the complete or partially melted glaciers to global sea level was shown to be in the range of 8.7 to 16 cm. As the authors noted:
“All projections for the twenty-first century show substantial mountain glacier and ice cap volume losses.”
Thus, knowing how these mountain glaciers might impact on us globally is important! As the paper finds, these small mountain glaciers are relatively large contributors to sea level rise. Yet as the author has stated, that is important as the small glaciers only represent 1 percent of the Greenland and Antarctic ice sheets, and therefore become easy to overlook.
Additionally worrying is the conclusion by the authors; that their predictions of sea level rise from glacial melt are likely to represent cautious estimates. This comes as a result of modelling only the surface mass balance, which is particularly important for the ice caps that were looked at in this study, as the ocean influence on melting could potentially be greater than surface melting. As seen in previous blog posts, this is particularly true for polar glaciers, where many come into contact with warm ocean waters.
Of course, there are several factors that weren’t consider, quite possibly due to limitations outside of the authors’ control. However, considerations of glacier depth through global measurements could provide a better indication of the differences between individual glaciers based on their thickness. And as discussed in the previous paper by Schaefer et al. (2009), no consideration was made of glacier debris, which could certainly have an effect on glacier melting up to the year 2100.
However, the authors did produce new findings which showed that the Himalayan glaciers (which are affected by debris cover) might potentially grow slightly by 2100. This again disproves the originally contentious IPCC statement that Himalayan glaciers could have disappeared by 2035. The results of this study showed that the ten climate models predicted between a 15 percent decline or possibly net growth by 2100. This slow shrinking or even growth could come as a result of increased snowfall in the future. Of course, the predictions elsewhere are more sobering; with a 50-90 percent loss predicted for the European Alps and a 60-85 percent loss for New Zealand’s Alps.
As one of the lead authors notes: “Most of them will be gone by 2100.”
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