Yorkshire Philosophical Society

Event Information

Accelerating loss of Alaskan Glaciers

Professor Bethan Davies, Newcastle University

The Juneau Icefield, Alaska, lost ice at an accelerated rate after 2005, relative to the past 250 years. Rates of area shrinkage were found to be 5 times faster from 2015–2019 than from 1979–1990. The continuation of this trend could push glacial retreat beyond the point of possible recovery.

Climate-driven ice loss from glaciers and icefields has been shown to contribute to rising sea-levels, with Alaska expected to remain the largest regional contributor to this effect up to the year 2100. Alaskan glaciers are particularly vulnerable to changes in the climate because they are often top-heavy (with more area at a higher altitude) and located on plateaus. In addition, these factors make Alaskan glaciers more prone to threshold behaviour, in which exceeding a tipping point could result in an irreversible recession. Longer-term records of Alaskan glacier change are needed to understand how climate change impacts these glaciers.

We used historical records, aerial photographs, 3D terrain maps, and satellite imagery to reconstruct Juneau Icefield glacier behaviour over the past 250 years. We observed steady glacier volume loss at a rate of approximately 0.65 km3 per year between 1770–1979. This rate accelerated to approximately 3 km3 per year between 1970–2010 and then doubled to 5.9 km3 per year between 2010–2020. This ice loss acceleration between 2010–2020 was accompanied by a glacial thinning rate 1.9 times higher than that from 1979–2000 and increased icefield fragmentation. This reduction in icefield accumulation area is contributing to a positive feedback loop, wherein surfaces such as darker rock are exposed, reducing solar reflectivity, and further contributing to the recession.

The findings suggest that a physical mechanism could be contributing to this icefield moving towards an irreversible tipping point in glacier recession. This greater understanding of Alaskan glacier ice loss mechanisms could improve projections of near-future sea level rise.

Joint lecture with PLACE and RGS (Royal Geographical Society)

7pm in the Tempest Anderson Lecture Theatre in the Yorkshire Museum

Image: Skiing across Taku Glacier

Member’s report

Many of us will have visited glaciers on our travels and been impressed by their massiveness and seeming permanence. However, as Prof. Bethan Davies, from Newcastle University, reminded us at the start of her lecture, glaciers are both beautiful but also vulnerable. More importantly, they are shrinking. Prof. Davies has made an icefield near the Alaskan capital city of Juneau her primary study system as she aims to gather empirical evidence about the extent of the icefield and how this has changed over time. In this fascinating lecture, which was delivered jointly with the Royal Geographical Society (RGS) and the PLACE Yorkshire organisation, we saw the products of her research that both combines modern satellite imagery with searches through historical sources to trace the retrenchment of the many glaciers in this region.

Moraines in the landscape are key indicators of the terminal position of glaciers and Davies is a big fan of them, spending time with her team trekking to various sites to confirm her satellite imagery, while avoiding bears, giant Alaskan moose and the ubiquitous mosquitoes! While the terminal moraines indicate the furthest reach of the glacier and modern satellite images show where they are now, Davies had to fill in the gaps and was able to use historical maps and aerial surveys to create a timeline of the Juneau icefield. What she found was alarming; not only are the glaciers retreating but the rate at which this occurs is increasing significantly, with a sharp upturn since 2005. A particular phenomenon she has observed is the ‘beheading’ of glaciers, which she has seen in Alaska but also in the Alps and Patagonia, where a break in the ice at the neck of the glacier leaves it detached and doomed to melt away.

This melting is happening at increasing rates on ice sheets around the world and we are losing about 260 billion tonnes of ice per year. We tend to think of climate change leading to small centimetre-scale increases in sea level, which are certainly enough to devastate many civilisations built on low-lying land. However, the estimate that if all the ice in Antarctica melts, then sea levels would rise by a staggering 58 metres is a calculation that has mind-boggling implications for mankind. While climate change is a politically highly charged topic, seeing this empirical evidence from the field directly, was an invaluable insight into how quickly our planet is changing.

Gavin Thomas