Seeing glaciers more clearly

Alaska’s glaciers are melting at some of the fastest rates on Earth, contributing significantly to sea-level rise as they respond to a rapidly warming climate. Despite this significance, scientists and glaciologists lack the consistent, high-resolution observations needed to track how these glaciers change from week to week. Between cloud cover, harsh conditions, and the vast scale of Alaska’s ice, circumstances have made it difficult to monitor melt behavior with the detail required to understand ongoing changes.

To address this challenge, a team of researchers developed a new remote sensing technique that uses a radar-based satellite to monitor glacier melt and the minimum elevation of snow lying on a glacier surface, or snowlines, across Alaska’s glaciers. The method, due to radar’s ability to penetrate clouds and function regardless of daylight, resulted in an eight-year record of detailed observations that were previously impossible to collect at this scale.

Their study, published in Nature Climate and Atmospheric Science, highlights how sensitive Alaska’s glaciers are to temperature changes, finding that each 1˚C increase in summer temperatures can lead to as many as three additional weeks of melt over the glacier. Their high-frequency observations also captured subseasonal events, such as a 2019 heat wave, during which snowlines in parts of Alaska rose by up to 105 meters, exposing as much as 28% more ice compared to typical years.

Their observations underscore the importance of monitoring glacier behavior over shorter periods of time – like weeks and months – especially as extreme heat events become more common, since these rapid changes are often missed by traditional satellite images.

“Consistent and reliable observations of glaciers at sub-seasonal or weekly scales offer unique opportunities to assess climatic impacts on glacier changes,” said Albin Wells, a civil and environmental engineering Ph.D. student at Carnegie Mellon University and lead author of the paper.

 “We leverage synthetic aperture radar satellite data to get around challenges associated with traditional methods derived from optical satellites, namely, that cloud cover and poor or varying lighting conditions encumber observations of the glacier surface,” Wells explained. “The radar-based data we leverage are unaffected by weather or light and only change when the glacier surface changes, which makes it ideal for the automated methods that we employ for over 3,000 glaciers.”

Comparing their radar-based measurements with existing satellite data demonstrated their technique’s viability, and with added advantages. Because radar can penetrate dry snow, it can detect a glacier’s underlying surface even after fresh snowfall, allowing researchers to identify the highest snowline each summer – a key indicator of glacier health – when optical satellites cannot.

This unprecedented level of detail revealed that Alaska’s glaciers could face one to four additional weeks of melt each summer by the end of the century depending on future emissions. Snowlines are also expected to rise earlier in the season, exposing more ice and making glaciers increasingly vulnerable, even in a typical year with no extreme weather events.

“This is the first time we’ve ever been able to consistently monitor when and where the glaciers are melting and how quickly the seasonal snow cover on the glacier is being lost. It’s like we’ve unlocked a treasure trove of data that is revealing how sensitive these glaciers are to changes in climate,” said David Rounce, assistant professor of civil and environmental engineering at Carnegie Mellon and co-author of the study. “This is important information that will ultimately help us improve our estimates of how glaciers will continue to change in the future.”

Though the study centers on Alaska, the technique is open-source, automated, and designed to be scaled and replicated, opening the door to near real-time glacier monitoring around the world. The data also provide valuable information for improving glacier models, which can help estimate future ice loss and sea-level rise.

By introducing a new method to observe glacier change and revealing how strongly glaciers react to heat waves and warming temperatures, researchers offer a clearer view of how Alaska’s ice is evolving, and what those changes might mean for the future.