Alaska's Top-Heavy Glaciers Are Melting, Approaching an Irreversible Tipping Point

The Juneau Icefield, one of North America's largest ice fields, is experiencing accelerated melting that may soon reach an irreversible tipping point. 

This stark conclusion comes from new research published in Nature Communications, revealing a grim future for this expansive ice field straddling the Alaska-Canada border near Juneau.

In the summer of 2022, researchers, including myself, skied across the flat, smooth plateau of the Juneau Icefield under a blazing sun. 

From this plateau, approximately 40 massive, interconnected glaciers descend toward the sea, surrounded by hundreds of smaller glaciers perched on mountain peaks. 

This seemingly tranquil scene hides a worrying reality: the ice field is rapidly losing mass, driven by rising temperatures and diminishing snow cover.

Our research highlights a troubling climate feedback loop at work on the Juneau Icefield. 

As temperatures rise, less snow remains through the summer, causing the "end-of-summer snowline" to climb higher. 

This exposes more ice to sunlight and higher temperatures, accelerating the melt and further reducing snow cover. 

This vicious cycle of melting and reduced snowfall threatens to plunge the icefield into a state of irreversible decline.

Juneau’s glaciers are top-heavy, with substantial ice and snow reserves at high altitudes. 

These reserves have traditionally sustained the lower glacier tongues. 

However, as the end-of-summer snowline creeps up to the plateau, a significant portion of these top-heavy glaciers becomes exposed to melting. 

This phenomenon is causing the icefield to thin rapidly, lowering the plateau and further exacerbating the melt.

Using satellite imagery, historical photographs, and geological markers, we measured the ice loss from the end of the last "Little Ice Age" (about 250 years ago) to the present day. 

Our data reveals a disturbing trend: while ice loss remained relatively constant until 1979, it accelerated significantly afterward. 

Between 2015 and 2019, the glaciers shrank five times faster than they did from 1979 to 1990.

The decreasing snow cover and lengthening summer melt season are darkening the icefield. 

Fresh, white snow, which reflects much of the solar energy, is giving way to older, darker snow and glacier ice that absorb more energy, increasing melt rates. 

This shift in surface characteristics is a critical factor driving the icefield toward an irreversible tipping point.

To understand the long-term behavior of glaciers and identify tipping points, we need extensive historical data. 

While satellite records provide a detailed picture of the past 50 years, we had to employ different methods to look further back. 

By mapping moraines—large piles of debris deposited at glacier snouts—and scoured bedrock, we reconstructed the icefield’s history over the past 250 years.

Our fieldwork included two weeks on the icefield and two weeks in the surrounding rainforest. 

Camping among moraine ridges, we took precautions against wildlife and endured the challenges of the rugged terrain. 

We also utilized aerial photographs from the 1940s and 1970s to complement satellite imagery, piecing together a 3D picture of the icefield.

The melting of the Juneau Icefield is not an isolated phenomenon. 

Glaciers worldwide are losing mass faster than the Greenland or Antarctic ice sheets. 

The thinning rates of these glaciers have doubled over the past two decades, underscoring the urgency of our research. 

Our long-term data series highlights the acceleration of glacier melt and the critical role of feedback mechanisms in this process.

Understanding how feedbacks accelerate glacier melt is essential for predicting future changes in these vital ice reserves. 

As the world continues to warm, the Juneau Icefield’s fate serves as a stark reminder of the broader impacts of climate change. 

Without immediate action to mitigate global warming, we risk pushing these top-heavy glaciers past their tipping point, triggering irreversible loss and profound ecological consequences.