One of the world’s largest icefields Alaska’s Juneau Icefield is melting at the fastest rate ever recorded, and now scientists have to fundamentally rethink both the extent and impact of glacial retreat. A recent study led by Newcastle University concluded that this rate of ice loss for the ice field has doubled over the past decade, a trend with much wider implications for global sea levels and climate change.
One such body of ice is the Juneau Icefield, which spans Alaska and British Columbia and holds 1,050 glaciers, most of them feeding from a central plateau into 40 larger ones. The record of this particular icefield dates as far back as 1770, making it one of the longest continuous datasets for scientists examining long-term changes. In a paper led by Professor Bethan Davies, Chair in Glaciology at Newcastle University, researchers combined a range of archival imagery and state-of-the-art modern remote sensing techniques to reconstruct the evolution of the icefield over the last 250 years.
Their findings are worrying. The rate of ice loss was relatively stable between 1770 and 1979 from 0.65 to 1.01 cubic kilometers per year. From there, this rate increased between 1979 and 2010 to between 3.08 and 3.72 cubic kilometers per year. But the most dramatic change occurred between 2010 and 2020 when the rate doubled to 5.91 cubic kilometers per year. “Change is dramatic and glacier mass loss is accelerating,” said Professor Davies.
The estimated total ice loss across the Juneau Icefield from 1770 to 2020 reaches 315.3 ± 237.5 cubic kilometers, nearly a quarter of its original volume. Such rapid melting resulted in the disappearance of 108 glaciers, while major thinning and fragmentation happened with the remaining ice.
One of the key factors quickening this melt is through the reduction of the icefields albedo, or reflectivity. Newly fallen snow is very reflective, but it melts away to older ice and debris that are much darker and more able to absorb heat, thus quickening further melting. This self-reinforcing cycle gets a further boost from rising snowlines, which expose more glacier ice to direct sunlight.
The team also reconstructed the extent of the icefield during the “Little Ice Age,” 250 years ago, at which time glaciers had much more extensive areas. That historical context gives scientists a baseline of natural behavior and provides a comparison for contemporary climate change.
Dr. Robert McNabb of Ulster University, a Lecturer in Remote Sensing, outlined the key role historical data played in gaining an understanding of long-term changes. “Piecing together thousands of archived aerial photographs to extract elevation gave us a detailed insight into the long-term behavior of the icefield,” he said.
The implications for the acceleration of melting are grim. Melting glaciers accelerate rising sea levels that threaten coastal communities around the world. They also interfere with freshwater supplies and affect the local ecosystem and wildlife. This need is brought into very sharp focus by the rapid retreat of the Juneau Icefield.
He expressed that if carbon emissions are reduced, then there would be less potential for further loss. “If we reduce carbon, then we have more hope of retaining these wonderful ice masses. The more carbon we put in, the more we risk irreversible, complete removal of them,” said Professor Davies.
The research findings tell us that most projections of glacier melting are currently understated for near-future loss of ice. Historical data integration into simulations of the future has been requested by the team to make a better understanding and accounting of accelerating melt behaviors.
This research, funded by the Juneau Icefield Research Program, the Royal Geographical Society, and the Geological Society of London, simply highlights that urgent action is required immediately to ensure the preservation of remaining icefields and the crucial functions they perform in our global ecosystem.