Ice melt poses dual sea rise and water access threat

Ice from Arctic Canada, like this small unnamed valley glacier and the Kaskawulsh glacier in the background in Saint Elias Mountains, Yukon Territory, will be among the largest contributors to sea level rise as ice caps and glaciers across the world melt in the 21st century. Credit: Christian Schoof.

Around one-fifth of the total volume of ice held in ice caps and glaciers will melt by 2100, adding around 12 cm to sea levels and threatening very low-lying coastal regions. That’s according to the latest simulations from Valentina Radić of the University of British Columbia, Canada and her US-based colleague Regine Hock from the University of Alaska, Fairbanks. “The problem will be floods and storm surges which also will be higher if the sea level is higher than today,” Radić told Simple Climate. She and Hock used detailed glacier measurements to model how the world’s ice will respond to predicted temperature changes. Their results, published in leading journal Nature Geoscience last Sunday, also show that Europe and New Zealand look set to lose around three-quarters of their glacier volume, impacting water supplies.

So far, there have been few predictions of what will happen to the world’s ice this century, and there has been large disagreement among those that have been produced. The resulting sea-level rise predictions range from a minimum of 5 cm to an extreme maximum of 36 cm. The issue, Radić explained, is that there are surprisingly few measurements of glaciers to begin predictions from. “The World Glacier Inventory today covers approximately 40 percent of the total ice area,” she said. “For the remaining 60 percent we still do not know how many glaciers there are, what is their surface area, elevation range, and so on.”

Worse still, less than one percent of the world’s glaciers have been measured for mass balance – the difference between the mass a glacier gains through the accumulation of snow, and what it loses – over the long term. “Observations of glacier mass balance are extremely important for the modellers,” Radić explained. “To reassure ourselves that the models are performing well, we need to validate their results with the ‘real world’. A lack of these observations presents a major obstacle for modelling of future glacier volume changes.”

Making ice models more solid

Just 40 percent of the world's ice area has currently been catalogued in the World Glacier Inventory, making predicting how the world's ice will respond to climate change challenging. Credit: Christian Schoof

While Radić concedes she and Hock weren’t able to completely resolve these issues, they were able to make progress. “We used an updated and more complete World Glacier Inventory than the one which was used in the previous studies,” she said. “Furthermore, we applied a more detailed modelling approach than the previous studies. However, the glacier mass balance observations for the past cannot be created now, and therefore this ‘lack of observations’ still remains as the largest source of uncertainties.”

The updated inventory contains 120,229 mountain glaciers and 2,638 ice caps. Hock and Radić studied the change in their ice volume with predicted temperature rises provided by ten state-of-the-art climate models. They based their predictions on Intergovernmental Panel on Climate Change (IPCC) scenario A1B, which assumes increasing equality between world regions with power generated by a balance of renewable and fossil-fuel technology.

To understand how glaciers would respond to the climate change predicted in different parts of the world, Hock and Radić produced a separate mass balance model. They tuned this with data from 36 glaciers, and checked it against another 80 glaciers to make sure it produced credible results. Then, after seeing how the World Glacier Inventory would be affected, they went on to project these changes to the rest of the world’s ice.

Glacial change no longer all that slow

Predictions of sea-level rise caused by ice melt provided by Radić and Hock's model in the 21st Century, in black, with the upper and lower limits of the range of statistical errors they calculate in red and blue respectively. From: Radić, V; Hock, R. "Regionally differentiated contribution of mountain glaciers and ice caps to future sea-level rise" Nature Geoscience, DOI: 10.1038/NGEO1052

The ten different climate models predicted sea level rises resulting from ice melt ranging from 7 cm to 18 cm by 2100, with an average of 12 cm. This is close to projections previously produced by the IPCC, which predict 7-17 cm sea level rise from ice melt. “In our projections the largest contributors to global sea-level rise are glaciers in the Arctic Canada, Alaska and Antarctica,” Radić said. “Some regions – the European Alps, New Zealand, Caucasus, West Canada and West US – though small absolute contributors to global sea-level rise, are projected to lose more than 50% of their current ice volume. This may have a significant impact on their water availability.”

Melting ice is not the only cause of sea-level rise – the water itself expands as it gets warmer – so the overall rise will be larger that the figure Radić and Hock produced. “Right now the total observed sea-level rise is about 2.5 mm/year,” Radić said. “Taking that the current contribution of these glaciers to sea level rise is about 1.1-1.4 mm per year, we project that this will increase to 1.6 mm per year, and for some models up to 2.0 mm per year. This is significant.”

Radić also pointed out that ice can contribute to sea level rise through calving, where lumps separate from tide-water glaciers to form icebergs, potentially accounting for roughly 30-40% of their total mass loss. Because the model she and Hock produced doesn’t include this, Radić says their figures are probably on the low side. “Incorporating calving into the models of glacier mass changes on regional and global scale is still a challenge and a major task for future work,” she added.