Researchers map 198,000 glaciers to improve sea-level rise estimates

As part of the RGI effort, the team mapped intricate glacier complexes in places like Alaska, Patagonia, central Asia and the Himalayas, as well as the peripheral glaciers surrounding the two great ice sheets in Greenland and Antarctica, said Pfeffer. “In order to model these glaciers, we have to know their individual characteristics, not simply an average or aggregate picture. That was one of the most difficult parts of the project.”

The team used satellite images and maps to outline the area and location of each glacier. The researchers can combine that information with a digital elevation model, then use a technique known as “power law scaling” to determine volumes of various collections of glaciers.

In addition to impacting global sea rise, the melting of the world’s glaciers over the next 100 years will severely affect regional water resources for uses like irrigation and hydropower, said Pfeffer. The melting also has implications for natural hazards like “glacier outburst” floods that may occur as the glaciers shrink, he said.

The total extent of glaciers in the RGI is roughly 280,000 square miles or 727,000 square kilometers — an area slightly larger than Texas or about the size of Germany, Denmark and Poland combined. The team estimated that the corresponding total volume of sea rise collectively held by the glaciers is fourteen to eighteen inches, or 350 to 470 millimeters.

The new estimates are less than some previous estimates, and in total they are less than 1 percent of the amount of water stored in the Greenland and Antarctic ice sheets, which collectively contain slightly more than 200 feet, or sixty-three meters, of sea rise.

“A lot of people think that the contribution of glaciers to sea rise is insignificant when compared with the big ice sheets,” said Pfeffer, also a professor in CU-Boulder’s civil, environmental and architectural engineering department. “But in the first several decades of the present century it is going to be this glacier reservoir that will be the primary contributor to sea rise.  The real concern for city planners and coastal engineers will be in the coming decades, because 2100 is pretty far off to have to make meaningful decisions.”

The release notes that part of the RGI was based on the Global Land Ice Measurements from Space Initiative, or GLIMS, which involved more than sixty institutions from around the world and which contributed the baseline dataset for the RGI. Another important research data tool for the RGI was the European-funded program “Ice2Sea,” which brings together scientific and operational expertise from 24 leading institutions across Europe and beyond.

The GLIMS glacier database and website are maintained by CU-Boulder’s National Snow and Ice Data Center, or NSIDC. The GLIMS research team at NSIDC includes principal investigator Richard Armstrong, technical lead Bruce Raup and remote-sensing specialist Siri Jodha Singh Khalsa.

NSIDC is part of the Cooperative Institute for Research in Environmental Sciences, or CIRES, a joint venture between CU-Boulder and the National Oceanic and Atmospheric Administration.

— Read more in  W. T. Pfeffer et al., “The Randolph Glacier Inventory: A Globally Complete Inventory of Glaciers,” Journal of Glaciology 60, no. 221 (2014) (DOI: 10.3189/2014JoG13J176)