First 'Atlas' of World Glaciers Reveals Dire Warning for Water-Scarce Future

Earth’s glaciers are melting as a result of human-driven climate change, a trend that has both local and global implications because glacial runoff provides freshwater to communities and ecosystems, while also contributing to sea level rise, which threatens coastal populations around the world.

Now, scientists led by Romain Millan, a postdoctoral scholar at the Institute of Environmental Geosciences in Grenoble, France, have produced the first global atlas of glacial movement and thickness, which reveals that the world’s glaciers have the potential to add an estimated 257 millimeters (10 inches) to sea level rise—roughly 20 percent less than previous estimates of about 13 inches. 

On the surface, this finding may sound like a rare piece of good news about rising sea levels, but Millan and his colleagues emphatically reject that characterization for a few reasons. Most importantly, the research raises alarms about freshwater availability in regions such as the tropical Andes Mountains, which contain 27 percent less glacial ice than previously calculated, according to the team’s study, which was published on Monday in Nature Geoscience. 

“The takeaway message is that we find, overall, that there is less ice in glaciers and it's bad news in terms of freshwater resources for people around the world,” Millan said in a call.

The team built this robust map of world glaciers from more than 800,000 images of Earth from space taken between 2017 and 2018 by the European Space Agency’s Sentinel-1 and Sentinel-2 satellites, and NASA’s Landsat-8 satellite. This space-down view covers 98 percent of Earth’s glaciers, some of which have never been ​​mapped before, including regions in Caucasus, New Zealand, and islands located off the coast of Antarctica.

The vast trove of data enabled the researchers to clock the velocity of glacial ice worldwide for the first time, adding a key missing piece of the puzzle compared to previous estimates of global glacial volume. The technique exposed some of the world’s fastest flowing ice, such as Penguin Glacier in Patagonia, which is moving at more than seven miles per year.

“Since 2013, there has been a revolution in satellite imagery,” Millan explained. “For example, with Sentinel-2, you can get a picture of the same glacier every five days, which has completely changed the way we look at glaciers. This allows us to really do a systematic mapping of the ice velocity of all the glaciers.”

“We mapped the ice velocity at a resolution of 50 meters” which “allows us to look at fine details in glaciers that was not possible in the past,” he added. “The ice velocity gives you a sense of where the ice is thin and where the ice is thick, and knowing that, we can re-estimate the volume of the world's glaciers.”

Overall, the results revealed that the world’s glaciers contain 11 percent less ice compared to previous estimates, though these ice deficits were not evenly distributed across the globe. Some regions contain far more ice reserves than previously estimated; the glaciers of the Himalayas, for instance, hold 37 percent more ice than suggested by past studies. 

However, communities in North Asia, which the team estimates may have 35 percent less ice than previously estimated, as well as those located in parts of the Andes Mountains, may be much more vulnerable to freshwater depletion in the future than anticipated. This finding has implications for millions of people who need freshwater not only to drink, but for crop irrigation and hydropower, among other applications.  

The new atlas can also improve projections of sea level rise, a trend that has consequences for coastal communities around the world. However, Millan noted that the study only models glaciers around the world, as opposed to massive ice sheets like those located in Greenland and Antarctica, which will be the major driver of sea level rise over the long term. While the researchers found that glaciers may contribute three fewer inches to rising sea levels, the loss of those massive ice sheets would still swamp that glacial contribution by hundreds of feet. 

Millan and his colleagues said that their findings will need to be bolstered by field surveys of the world’s glaciers, which will double-check the satellite observations from the ground. Even so, the study represents a quantum leap in our understanding of global glacier cover, with major implications for scientists in the field as well as policy-makers hoping to mitigate the effects of human-driven climate change.

“This new geometry is more coherent in time, and captures the shape of the glaciers in a much better way, which changes everything for the future evolution of glaciers,” Millan concluded.