A new atlas reveals that the globe’s glaciers have fewer ic

HANNOVER, NH – February 7, 2022 – The first atlas to measure the movement and thickness of the world’s glaciers gives a clearer but mixed picture of the globe’s ice-related freshwater resources, according to Institute researchers of Environmental Geosciences (IGE) and Dartmouth College.

The global survey, published in nature geoscience, measures the speed and depth of more than 250,000 mountain glaciers. The research revises previous estimates of glacial ice volume, now suggesting that there is 20% less ice available for sea level rise in the world’s glaciers than previously thought.

The findings have implications for the availability of water for consumption, power generation, agriculture and other uses around the world. The results also change projections of climate-induced sea level rise that is expected to affect people around the world.

“Determining the amount of ice stored in glaciers is a key step in anticipating the effects of climate change on society,” said Romain Millan, postdoctoral researcher at IGE and lead author of the study. “With this information, we will be closer to knowing the size of the largest reservoirs of glacial water and also to considering how to respond to a world with fewer glaciers.”

“Finding less ice is significant and will have implications for millions of people around the world,” said Mathieu Morlighem, Evans Family Professor of Earth Sciences at Dartmouth and co-author of the study. “Even with this research, however, we still don’t have a perfect picture of how much water is actually locked up in these glaciers.”

The new atlas covers 98% of the world’s glaciers. According to the study, many of these glaciers are shallower than previously estimated in research. Double counting of glaciers along the peripheries of Greenland and Antarctica has also obscured previous data sets.

The study found less ice in some regions and more ice in others, with the overall result that there is less glacial ice in the world than previously thought.

Research has found that there is almost a quarter less glacial ice in the tropical Andes of South America. This discovery means that there is up to 23% less fresh water stored in a region that millions of people depend on every day. Reducing this amount of fresh water is equivalent to completely drying up Mono Lake, California’s third largest lake.

On the contrary, the Himalayan mountains of Asia were found to have more than a third more ice than previous estimates. The result suggests that around 37% more water resources could be available in the region, although the continent’s glaciers are melting rapidly.

“The general trend of warming and mass loss remains unchanged. This study provides the picture needed for models to offer more reliable projections of how long these glaciers have left,” Morlighem said.

The melting of glaciers due to climate change is one of the main causes of sea level rise. Glaciers are currently estimated to contribute 25-30% of global sea level rise, threatening around 10% of the world’s population living below 30 feet above sea level.

The 20% reduction in glacial ice available for sea level rise reduces the potential for sea level glacial contribution by 3 inches, revising it down from 13 inches to just over 10 inches. This projection includes contributions from all of the world’s glaciers except for the two large ice sheets of Greenland and Antarctica, which have a much larger potential contribution to sea level rise.

“Comparing global differences with previous estimates is only one side of the picture,” Millan said. “If you start looking locally, the changes are even greater. To correctly project the future evolution of glaciers, capturing fine detail is far more important than total volume.

According to the study, depth measurements previously existed for only about 1% of the world’s glaciers, with most of these glaciers only partially studied.

The glacial ice estimates that existed before the new study were almost entirely uncertain, according to the research team. The uncertainty is due, in part, to the lack of ice flow measurements indicating the location of thick and thin ice, all of which are collected by indirect techniques.

To create the massive glacier flow database, the research team studied more than 800,000 satellite image pairs of glaciers, including large ice sheets, narrow alpine glaciers, slow valley glaciers and fast tidal glaciers. The high-resolution images were acquired between 2017 and 2018 by NASA’s Landsat-8 and European Space Agency’s Sentinel-1 and Sentinel-2 satellites. The data was processed using over one million hours of computation at IGE.

“We usually think of glaciers as solid ice that can melt in the summer, but the ice actually flows like thick syrup under its own weight,” Morlighem said. “Ice flows from high altitudes to lower altitudes where it eventually turns to water. Using satellite imagery, we are able to track the movement of these glaciers from space on a global scale. and, from there, to deduce the quantity of ice in the whole world.

The resulting first global flow velocity map covers most of the world’s terrestrial glaciers, including areas where no mapping previously existed, such as the Southern Cordilleras of South America, the Subantarctic Islands and New -Zealand.

Although the new atlas marks a major improvement in estimates of ice and glacier water potential, the thickness distribution of the world’s glaciers is still subject to large information gaps.

“Our estimates are closer, but still uncertain, especially in areas where many people depend on glaciers,” Millan said. “Collecting and sharing measurements is complicated because glaciers are spread across many countries with different research priorities.”

According to the team, without direct measurements on the ground, the estimate of the freshwater resources of the glaciers will remain uncertain.

The study calls for a reassessment of the evolution of the world’s glaciers in numerical models as well as direct observations of ice thicknesses in the tropical Andes and Himalayas, which are great water towers but remain poorly documented.

Jérémie Mouginot and Antoine Rabatel, from the Institute of Environmental Geosciences (IGE) – Grenoble Alpes University, from the National Center for Scientific Research (CNRS), from the National Research Institute for Sustainable Development (IRD) and engineering and management colleges made important contributions to the study. Millan and Morlighem conducted some of the research at the University of California at Irvine. Millan is also affiliated with the CNRS and the Department of Geosciences and Natural Resource Management at the University of Copenhagen. The research was supported by France’s Center National d’Etudes Spatiales (CNES).

###

Images: https://www.dropbox.com/sh/psevwei4ct6x9j7/AABpVsYOzXMGEZKb0yeeq1O8a?dl=0

All media images were originally produced by Jean Baptiste Barré of Grenoble Alpes University.

Dartmouth Media Contact (US EST; GMT-5): david.s.hirsch@dartmouth.edu
IGE media contact (France CET; GMT+1): anne.chapuis@univ-grenoble-alpes.fr

IGE on Twitter: @IGE_grenoble
Dartmouth on Twitter: @dartmouth

About Dartmouth
Founded in 1769, Dartmouth is a member of the Ivy League and consistently ranks among the top academic institutions in the world. Dartmouth has forged a singular identity for combining its deep commitment to exceptional liberal arts and undergraduate higher education with distinguished research and scholarship in the arts and sciences and its four main graduate schools – the Geisel School of Medicine, the Guarini School of Graduate and Advanced Studies, Thayer School of Engineering, and the Tuck School of Business.

About the Institute of Environmental Geosciences (IGE)
The Institute of Environmental Geosciences (IGE) is a joint research unit (CNRS, IRD, UGA, Grenoble INP) which brings together around 250 people. The IGE is part of the Observatory of Sciences of the Universe of Grenoble (OSUG). IGE’s projects are centered on the study of the climate and the anthropization of our planet, in particular in the regions where the societal and environmental stakes are the most important: the polar regions, the intertropical zone and the regions of Mountain.