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Half of the world’s glaciers will melt by 2100

As glaciers melt and lose mass, they will contribute to sea-level rise. It is already estimated that meltwater from all glacial land ice (excluding the Greenland and Antarctic ice sheets) has contributed 21 percent of the sea-level rise recorded between 2000 and 2019. In addition, melting glaciers will change available water resources for around 1.9 billion people, altering annual and seasonal runoff for personal use and agriculture, and contributing to water insecurity. 

Melting glaciers will also increase the frequency and magnitude of glacier-related hazards, such as landslides and outburst floods, over the next century. For all these reasons, it is critical to predict and understand the magnitude, spatial pattern, and timing of glacier mass loss.

In a new study that represents “a substantial step forward in predictive modeling” of glacier response to climate change, a team of international researchers has developed a model predicting the fate of all 215,547 of the world’s mountain glaciers (excluding those on the Greenland and Antarctic ice sheets) under various different warming scenarios. Their findings emphasize that, even if warming is limited to the target 1.5oC, all glaciers will be under threat by the end of 2100.

The study uses new and more detailed data sets on glacier mass balance and rates of ablation, and represents glacier dynamics with a flowline model. The researchers also consider important physical processes that have not been incorporated in previous models, and provide model predictions for global warming at 1.5oC, 2oC, 3oC and 4oC above pre-industrial levels, all the way to the year 2100. In a related perspective of the research, a commentator referred to this model as the “most comprehensive so far.”

The findings, published in the journal Science, predict that, globally, glaciers will lose between 26 percent (+1.5°C) and 41 percent (+4°C) of their mass by 2100, relative to a 2015 baseline. This mass loss would increase mean sea level by between 90 (+1.5°C) and 154 (+4°C) mm SLE, representing a 71 percent increase between the +1.5°C and +4°C scenarios.

The researchers report that, even in the most optimistic scenario of limiting global warming to 1.5 oC above pre-industrial levels, their model predicts that nearly 60 percent of the world’s glaciers will be lost by 2100. Within 2°C, the agreed warming limit of the Paris Agreement, about 70 percent of the smaller glaciers and 20 percent of the larger ones will melt completely. Considering that estimates from COP26 predict a global mean temperature increase of around 2.7°C by 2100, even the very largest glaciers in the Polar Regions will be under threat. 

And the consequences do not stop at 2100. Even if temperature is stabilized at any level, the glaciers that remain will continue to lose mass beyond the model’s 2100 end point. These dire predictions highlight the need to act now in order to prevent substantial glacier loss.

“Every increase in temperature has significant consequences with respect to glacier contribution to sea level rise, the loss of glaciers around the world, and changes to hydrology, ecology, and natural hazards,” wrote the study authors, led by David Rounce of the Department of Civil and Environmental Engineering at Carnegie Mellon University and the Geophysical Institute at the University of Alaska Fairbanks.

In a related Perspective (also published in Science), Guðfinna Aðalgeirsdóttir and Timothy James say it is important to frame these findings in a positive light in order to motivate the public to support climate change policies. They say the authors of this study, “. . . while issuing a stark warning about the consequences of insufficient action, achieve this framing with an important message: Although it is too late to avoid losing many glaciers, any effort to limit global mean temperature rise will have a direct effect on reducing how many glaciers will be lost.”

The new model reveals a strong linear relationship between global mean temperature increase and glacier mass loss, meaning that, no matter how small the increase in global mean temperature, it will lead to increased glacier loss and added sea-level rise. And if temperatures were to increase by +2.7°C, as predicted at COP26, Earth will likely experience a near-complete deglaciation of entire mid-latitude regions by 2100, including Central Europe, Western Canada and United States, and New Zealand, which will add more to sea-level rise than is currently estimated.

In conclusion, the researchers stress the urgency of establishing more ambitious climate pledges to preserve the glaciers in the mountainous regions of the world. It may be too late to prevent the loss of many glaciers, but because of the linear relationship between temperature rise and ice mass loss, any action that is taken to limit warming will have a direct effect on reducing the number of glaciers lost.

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By Alison Bosman, Staff Writer

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