A large ice field stretching across Alaska in the US and British Columbia in Canada could reach an irreversible tipping point sooner than predicted as its glaciers have been rapidly receding since 2005, a new study says.

The study was published in Nature communicationfocused on the Juneau Icefield in Alaska. This plateau icefield consisted of 1,050 glaciers in 2019 and covered an area of ​​3,816.3 square kilometers. The study found that glacier retreat was five times faster from 2015 to 2019 than between 1948 and 1979.

“We know that Alaska’s glaciers contribute significantly to sea level rise – more than any other glacial region,” said Bethan Davies, lecturer at Newcastle University and lead author of the study, in an interview with Down to earth.

Alaska's vast ice fields contain so much glacial ice that if it melted, global sea levels would rise by 46.4 millimeters. About 25 percent of global glacial ice loss is attributed to Alaska's glaciers, which lose about 66.7 billion tons of ice each year. If things continue at this rate, all of Alaska's ice could be gone in about 250 years, the researchers warned.

Davies found that glacier mass loss in Alaska is accelerating, but scientists lack a longer-term time frame to determine the full extent of this trend. To investigate this, Davies and her colleagues from the United States and Europe studied the long-term response of glaciers to climate change to understand the accelerating rate of glacier mass loss and the processes that amplify this melting. This knowledge will improve our ability to predict how ice fields might respond to future climate change.

The team wanted to determine the shrinkage and thinning rates of the entire ice field to quantify glacier changes from the “Little Ice Age” (a period of widespread cooling that lasted from 1303 to 1850) to the recent past (2020). The reconstructed Little Ice Age revealed that the ice field covered 5,414.95 square kilometers of land, about 30 percent more than in 2019. From 1770 to 2013, glacier volume loss was 0.4 cubic kilometers per year.

Between 1770 and 2019, 108 glaciers disappeared, and 100 percent of glaciers mapped in 2019 had receded compared to their positions during the Little Ice Age. This loss coincided with a temperature increase that increased 1.39°C at the Juneau airport from 1941 to 2020, with a notable shift in the 1970s.

The researchers attributed this temperature increase to a shift towards predominantly positive values ​​of the Pacific Decadal Oscillation (PDO) starting in 1976. The PDO is a long-term ocean fluctuation in the Pacific Ocean that alternates between warm and cool phases approximately every 20 to 30 years. The positive PDO values ​​brought increased precipitation and warmer temperatures in Alaska and Juneau.

Between 1948 and 1979, glacier volume loss was 1.0 cubic kilometers per year, increasing to 3.7 cubic kilometers per year from 1979 to 2000. Temperatures remained relatively stable from 1990 to 2005, as did ice field thinning and area loss. However, from 2010 to 2020, the region experienced a further increase in temperatures.

Glacier volume loss increased from 3.1 cubic kilometers per year between 2000 and 2010 to 5.9 cubic kilometers per year between 2010 and 2020. “Alaska's ice fields – predominantly flat plateau ice fields – are particularly vulnerable to accelerated melting as the climate warms because ice loss occurs across the entire surface, thus affecting a much larger area,” Davies said in a statement.

A major factor in glacier volume loss is the increasing equilibrium altitude (ELA), the zone on a glacier where snow and ice accumulation and loss balance out over a year. As summers become longer and winters shorter and temperatures rise, the altitude at which snow remains year-round increases.

“The flat plateau used to be above the ELA, and snow was present all year round. Now that the ice on the plateau is melting, the snow line is on the plateau itself during particularly warm summers. Because the plateau is very flat, a small increase in the ELA exposes a much larger area to melt, accelerating the mass loss of the ice field,” explained Davies.

The team also hopes to examine longer-term records of ice field changes, particularly from earlier periods of rapid climate change, such as during the last ice age-interglacial transition 19,000 to 11,000 years ago.