Clark professor studies glacier contributions to sea level rise

Ninety-nine percent of all of Earth’s land ice is locked up in the massive Greenland and Antarctic ice sheets. However, according to a new study led by Alex Gardner, assistant professor in the Clark University Graduate School of Geography, “the world’s other land ice stored in glaciers—humble repositories of the remaining 1 percent of land ice—contributed just as much to sea level rise as the two ice sheets combined over the period 2003 to 2009.”

Alex Gardner Asst. Prof. Alex Gardner

“For the first time we’ve been able to very precisely constrain how much these glaciers, as a whole, are contributing to sea level rise,” said Gardner, who is the main author of the study “A Reconciled Estimate of Glacier Contributions to Sea Level Rise: 2003 to 2009,” published in the May 17 issue of Science magazine. “And what we find is that melting of these smaller ice bodies account for one third of observed sea level rise.”

The research, which uses multiple satellites and an extensive collection of ground data, involved the efforts of 16 researchers from 10 countries, with major contributions from Clark University, the University of Michigan, Scripps Institution of Oceanography, Trent University, the University of Colorado at Boulder, and University of Alaska Fairbanks.

According to the authors, previous estimates of the recent contribution of glaciers to sea level rise have differed widely. Their study compares traditional ground measurements to satellite data from NASA’s Ice, Cloud, and land Elevation Satellite (ICESat) and Gravity Recovery and Climate Experiment (GRACE) missions to come up with optimal mass change estimates for glaciers in all regions of the planet.

The new research found that all glacierized regions lost mass from 2003 to 2009, with the biggest ice losses occurring in Arctic Canada, Alaska, coastal Greenland, the southern Andes and the Himalayas. In contrast, Antarctica’s peripheral glaciers – smaller ice bodies not connected to the main ice sheet – contributed little to sea level rise during that period. This differs from previously published estimates for the period 1961-2004, which showed that these bodies accounted for 30 percent of the global mass loss from glaciers.

a glacial erratic Gardner stands next to a glacial erratic, a massive rock that is being transported tens of kilometers on the surface of a glacier that will eventually end up in the ocean.

Traditional estimates of glacier mass loss, based solely on field measurements and localized observations, can sometimes overestimate ice loss when the findings are extrapolated over larger regions with few observations, like entire mountain ranges, said Gardner.  The study concluded that, although ICESat and GRACE each have their own limitations, “their estimates of mass change for large glacierized regions agree very well, which gives us strong confidence in our results.”

Gardner said the findings have serious implications for past assessments.

“We conclude that a thorough reexamination of past estimates of glacier contributions to sea level rise is needed,” he said.

An abstract of the paper is available at

This research builds on Gardner’s earlier work that found that in recent years the Canadian Arctic glaciers have become the largest glacier contributors to sea level rise outside of Greenland and Antarctica. This earlier work was published in 2011 in the journal Nature; Gardner joined the Clark University faculty in September of 2012.

In his research on the Earth's cryosphere, Gardner integrates remote sensing observations and Earth system modeling to study how glaciers and ice sheets respond to natural and human-induced changes in the environment as well as how changes in the reflectivity of snow and ice modify the Earth's climate. He is now focused on assessing glacier wastage on a global scale and is a contributing author of the upcoming Intergovernmental Panel on Climate Change's Fifth Assessment Report, due to be released publicly in October 2014.

Science is the weekly journal of the American Association for the Advancement of Science (AAAS) and is considered the world's leading journal of original scientific research, global news, and commentary.

NASA’s press release is located at:

For more images of glaciers and sea level rise go to