Ice melting from glaciers around the world is depleting regional freshwater resources and driving global sea levels to rise at ever-faster rates, according to a new study by an international research consortium that includes scientists from the University of Arizona. 

"Today, glaciers are melting 36% faster than they did 20 years ago," said Christopher Harig, an assistant professor in the U of A Department of Geosciences who co-authored the study, published in Nature. "Our research revealed that glaciers have been losing an average of 273 billion tons of ice per year during that timeframe."

The study showed that in the year 2000, glaciers – excluding the continental ice sheets of Greenland and Antarctica – spanned 272,287 square miles and held an estimated 134,182 billion tons of ice. Over the past two decades, global glacier volume has shrunk about 5%, with regional losses ranging from 2% on the Antarctic and Subantarctic Islands to 39% in central Europe. 

The amount of ice being lost jumped by 36% in the second half of the study period (2012-2023) compared to the first half (2000-2011). Glacier mass loss over the whole study period was 18% higher than that of the Greenland ice sheet and more than double that of the Antarctic ice sheet.

"Glacier ice loss is a key part of sea-level rise today, and we expect it to get even larger in the future," Harig said. "Coastal communities depend on sea-level rise estimates and future predictions for their planning. These large group studies that bring together international scientists are critical to ensuring we are making the best measurements possible." 

Sea level rise: Like stacking credit cards

Between 2000 and 2023, glaciers collectively lost 7,211 billion tons of ice, contributing almost three quarters of an inch to global sea-level rise. On average, glaciers lost 301 billion tons of ice per year, equivalent to an annual sea-level rise equaling .03 inches – about the thickness of a credit card. The rate of glacier ice loss has increased significantly from 254 billion tons per year in the first half of the study period to 346 billion tons per year in the second half.

Glaciers rank as the second-largest contributor to global sea-level rise, following ocean warming-related thermal expansion. In addition to rising sea levels, glacier melt represents a significant loss of regional freshwater resources.

"To put this in perspective, the 273 billion tons of ice lost annually amounts to what the entire global population consumes in 30 years, assuming 3 liters per person and day," said the project's scientific co-lead, Michael Zemp of the University of Zurich.

"Glaciers are vital freshwater resources, especially for local communities in Central Asia and the Central Andes, where glaciers dominate runoff during warm and dry seasons," said co-author Inés Dussaillant, a glaciologist at the University of Zurich. 

The study was conducted as part of the Glacier Mass Balance Intercomparison Exercise, or GlaMBIE, with the goal of generating a community estimate of global glacier mass loss. GlaMBIE is a major research initiative coordinated by the World Glacier Monitoring Service, hosted at the University of Zurich, in collaboration with the University of Edinburgh and Earthwave, a UK-based data science company. 

Compiling 233 estimates of regional glacier mass changes from about 450 data contributors organized in 35 teams allowed the researchers to take advantage of different observation methods. Analyzing field measurements and data obtained with optical, radar, laser and gravimetry satellites, the GlaMBIE collaboration produced an annual time series of glacier mass changes for all glacier regions globally from 2000 to 2023. 

Eric Cicero, a doctoral student in Harig's group, is a co-author on the paper. Funding for the project was provided primarily by the Science for Society element of the European Space Agency's FutureEO program, with additional support from the International Association for Cryospheric Sciences and various institutional partners. It was conducted by the GlaMBIE team under the leadership of the World Glacier Monitoring Service and University of Edinburgh, and in collaboration with Earthwave and over 30 other research teams from around the world.