Around the World, Small Mountain Glaciers Add to Sea Level Rise

Three things you should know:

1) Increasing global temperatures cause sea level rise in two distinct ways. One way is through expansion, since the volume of the oceans expand as the water warms. Another takes place when glaciers of all sizes melt, because they add extra water to the sea.

2) Computer models are used to predict how much the melting ice will contribute to future sea level rise, but uncertainty in these models makes it difficult to pinpoint a narrow range for sea level rise. 

3) The melting of small mountain glaciers and icecaps from all continents is expected to contribute about 12 cm to global sea level rise by 2100, according to a new study.

The Debrief:

The Tabuchet glacier on  La Meije in the French Alps is an example of a small glacier, many of which are melting and contributing to sea level rise. Credit: Gilles 92, flickr

Small mountain glaciers and ice caps, like those scattered among the uppermost regions of the Rocky Mountains, make up only about one percent of the world’s total ice cover. But while the massive continental ice sheets in the Arctic and Antarctic dwarf the small mountain glaciers, researchers say that melting from these smaller glaciers contributes a disproportionately large amount to global sea level rise, and could account for as much as 25 percent of sea level rise by 2100.

Until now, most research on how much melting ice may contribute to rising sea levels has neglected the small glaciers.

“Most studies are focused on the big ice sheets, with just a few looking at how much the small glaciers will contribute to sea level rise,” says glaciologist Valentina Radic from the University of British Columbia in Vancouver, Canada. To get a better idea of the role small glaciers will play, Radic carried out a study of all the world’s known small glaciers to predict how much ice they are bound to lose over the next 90 years. The results have recently been published in the journal Nature Geoscience.

Using a series of ten global climate computer models, Radic investigated how much small glaciers all over the world are expected to shrink as temperatures warm and precipitation patterns change. Her analysis included over 120,000 glaciers worldwide, which are all found in a global inventory of glaciers. According to Radic, the combination of climate models allowed her to focus on the glaciers region-by-region around the world, getting projections with finer levels of detail than has been collected before.

In total, Radic’s models predict that melting from the world’s small mountain glaciers will lead to nearly five inches of sea level rise by 2100. Of these, glaciers in Alaska, Arctic Canada, and Greenland are expected to contribute the most, she says. Though the amount of water added to the oceans from these glaciers will still be smaller than the amount coming from large ice sheet melting, they contribute a disproportionately large amount, Radic says, because the temperature changes occurring in areas of the world where these small mountain glaciers are located are, in many cases, hovering around the melting point of ice. In these areas, a run of above average warm weather might bring the temperature well above freezing, causing a lot of additional melting. 

Why this science matters:

In general, there are two different factors contributing to sea level rise. Firstly, the volume of the water already in the oceans expands as the water temperature increases, and about 25 percent of future sea level rise will be caused by this thermal expansion. A full half of sea level rise, on the other hand, will come from melting of the large continental ice sheets in the Arctic and Antarctic as global temperatures climb higher. The remaining portion of sea level rise will come from the melting of smaller glaciers spread around the world at high altitudes.

Though researchers already expect that small mountain glaciers will play an important role in sea level rise, only a few studies have focused on this distinct collection of ice. Consequently, there is a wide range of estimates of just how much seas will rise from these small glaciers. This new analysis has examined the role small mountain glaciers will play in future sea level rise by modeling glacial changes region-by-region around the globe.

The five inches of sea level rise that Radic’s results predicts is comparable to the range reported in the Fourth Assessment Report from the U.N. Intergovernmental Panel on Climate Change (IPCC) in 2007, but the IPCC’s analyses have not had the regional focus that Radic’s new study had. “In a way, we can say that for some regions, the IPCC just gave a guess [about sea level rise],” she explains. “Now, we’ve shown that their guess was right. We have a more credible model and we can now say that these small glaciers are important for sea level rise.”

Though Radic’s study has looked at the sea level contribution from small glaciers with more detail than has previously been done, she says there are still limitations to the data. Although the study covered over 120,000 mountain glaciers, this represents only about 40 percent of the world’s small glaciers. In coming years, the global glacial inventory will continue to take stock of the world’s smaller glaciers, since only then can a more reliable prediction be made of their future contribution to sea level rise.

Furthermore, Radic says her analysis did not include any ice lost from small glaciers by calving events, where large chunks of ice break off from the outside edges of the glaciers. “It might be that we’re still on the low end because we didn’t include glacial calving,” she explains. But some people predict that as much as 30 percent of the loss of glaciers is due to calving, Radic says, so although “we don’t yet have enough data to model ice lost because of glacial calving, it’s an important problem to look at in the future.”