Melting of Alaskan glaciers accelerating faster than previously thought

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Juneau Icefield
Large, flat, upper plateau of the Juneau Icefield that is vulnerable to rapid melting as climate warms. Embedded Jacob Bendle, researcher at NGU. Photo: Bethan Davies and NGU

Melting of glaciers in a major Alaskan icefield has accelerated and could reach an irreversible tipping point earlier than previously thought, new research suggests.

(This is a press release from Newcastle University, edited and quality assured by members of NGU's staff)

The research, conducted by a team from the UK, USA and Europe, and including researcher Jacob Bendle from the Geological Survey of Norway (NGU), found that glacier loss on Juneau Icefield, which straddles the boundary between Alaska and British Columbia, Canada, has increased dramatically since 2010.

Back to 1770

The team looked at records going back to 1770 and identified three distinct periods in how icefield volume changed. They saw that glacier volume loss remained fairly consistent from 1770 – 1979 at between 0.65- 1.01 km3 per year, increasing to 3.08-3.72 km3 per year between 1979-2010. Between 2010-2020 there was a sharp acceleration when the rate of ice loss doubled, reaching 5.91 km3 per year.

In particular, the research, published in Nature Communications, found that icefield-wide, rates of glacier area shrinkage were five times faster from 2015-2019 relative to 1948-1979.

Overall, the total ice loss across the Juneau icefield between 1770-2020 (315.3 ± 237.5 km3) equated to just under a quarter of the original ice volume.

The increased rate of glacier thinning has also been accompanied by increased glacier fragmentation. The team mapped a dramatic increase in disconnections, where the lower parts of a glacier become separated from the upper parts. Additionally, 100% of glaciers mapped in 2019 have receded relative to their position in 1770, and 108 glaciers have disappeared completely.

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The disconnection of a glacier tongue from its source area
The disconnection of a glacier tongue from its source area due to ice thinning. Photo: Bethan Davies
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Bedrock at high elevation recently exposed
Bedrock at high elevation recently exposed by the thinning and retreat of ice. Photo: Bethan Davies

“Incredibly worrying”

Study lead, Dr Bethan Davies, Senior Lecturer, Newcastle University, UK, said: “It’s incredibly worrying that our research found a rapid acceleration since the early 21st century in the rate of glacier loss across the Juneau icefield.

“Alaskan icefields – which are predominantly flat, plateau icefields - are particularly vulnerable to accelerated melt as the climate warms since ice loss happens across the whole surface, meaning a much greater area is affected. Additionally, flatter ice caps and icefields cannot retreat to higher elevations and find a new equilibrium.  

“As glacier thinning on the Juneau plateau continues and ice retreats to lower levels and warmer air, the feedback processes this sets in motion is likely to prevent future glacier regrowth, potentially pushing glaciers beyond a tipping point into irreversible recession.”

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Kart som viser krympingen av isbreflaten
Yearly change in the height of glacier surfaces (meters) on the Juneau Icefield between 1948-1979, 1979-2000, 2000-2010 and 2010-2020. The red areas show ice loss and blue areas show ice gain. The maps show that the rate of ice loss increased in the late 20th and 21st centuries. The yellow dots show areas where glacier tongues have split from the upper plateau due to thinning of the ice. The number of “disconnections”, as they are known, also increased dramatically in the late 20th and 21st centuries.
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Kart som viser hastigheten på isavsmeltingen.
The mapped change in glacier area over part of the Juneau Icefield, showing the progressive shrinkage of glaciers over the 20th and 21st centuries.

Sea level rise

Alaska contains some of the world’s largest plateau icefields and their melting is a major contributor to current sea level rise. The researchers think the processes they observed at Juneau are likely to affect other, similar icefields elsewhere in the world, including in Norway.

Dr Jacob Bendle, researcher at NGU said: “The processes we observed at the Juneau icefield could be important for Norwegian icefields with flat plateaus in their upper parts – such as Svartisen or Hardangerjøkulen – as such glacier types are likely susceptible to rapid melting as the climate warms at higher altitudes.”

The team also say current published projections for the Juneau icefield that suggest ice volume loss will be linear until 2040, accelerating only after 2070, may need to be updated to reflect the processes detailed in this latest study.

Dr Davies said: “This work has shown that different processes can accelerate melt, which means that current glacier projections may be too small and underestimate glacier melt in the future.”

Long-term behaviour

The team used a combination of historical glacier inventory records, 20th century archival aerial photographs, and satellite imagery as well as geomorphological mapping conducted during fieldwork in 2022 to piece together a comprehensive picture of changes over the past 250 years.

Dr Robert McNabb, Lecturer in Remote Sensing, Ulster University, said: "What was really exciting about this research was piecing together thousands of archived aerial photographs to extract elevation, which gave us a really detailed insight into the long-term behaviour of the icefield.

“Putting together this archive of photographs, collected 70 and 50 years ago, was a little like doing the world's hardest jigsaw puzzle but the quality of the imagery meant we were able to reconstruct the icefield elevation in the pre-satellite era for the first time. Longer term archives like this one are an incredibly valuable resource, as they give us a much better understanding of the thresholds for accelerating change, as we've seen on the Juneau Icefield.”

Reference: Davies, B., McNabb, R, Bendle, J., et al. (2024) ‘Accelerating glacier volume loss on Juneau icefield driven by hypsometry and melt-accelerating feedbacks’, Nature Communications.

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