Team projects 2 out of 3 glaciers could be lost by 2100
COLLEGE OF ENGINEERING, CARNEGIE MELLON UNIVERSITY
IMAGE: GLACIERS FROM A RESEARCH EXPEDITION view more
CREDIT: CARNEGIE MELLON COLLEGE OF ENGINEERING
Assistant Professor David Rounce of Civil and Environmental Engineering led an international effort to produce new projections of glacier mass loss through the century under different emissions scenarios. The projections were aggregated into global temperature change scenarios to support adaptation and mitigation discussions, such as those at the recent United Nations Conference of Parties (COP 27). His work showed that the world could lose as much as 41 percent of its total glacier mass this century—or as little as 26 percent—depending on today’s climate change mitigation efforts.
Specifically, Rounce and his team found that in a future scenario with continued investment in fossil fuels, over 40 percent of the glacial mass will be gone within the century, and over 80 percent of glaciers by number could well disappear. Even in a best-case, low-emissions scenario, where the increase in global mean temperature is limited to +1.5° C relative to pre-industrial levels, over 25 percent of glacial mass will be gone and nearly 50 percent of glaciers by number are projected to disappear. A majority of these lost glaciers are small (less than one km2) by glacial standards, but their loss can negatively impact local hydrology, tourism, glacier hazards, and cultural values.
His work provides better context for regional glacier modeling, and he hopes it will spur climate policymakers to lower temperature change goals beyond the 2.7° C mark that pledges from COP-26 are projected to hit. Smaller glacial regions like Central Europe and Western Canada and the United States will be disproportionately affected by temperatures rising more than 2° C. At a 3° C rise, glaciers in these regions almost disappear completely.
Rounce noted that the way in which glaciers respond to changes in climate takes a long time. He describes the glaciers as extremely slow-moving rivers. Cutting emissions today will not remove previously emitted greenhouse gasses, nor can it instantly halt the inertia they contribute to climate change, meaning even a complete halt to emissions would still take between 30 and 100 years to be reflected in glacier mass loss rates.
Many processes govern how glaciers lose mass and Rounce’s study advances how models account for different types of glaciers, including tidewater and debris-covered glaciers. Tidewater glaciers refer to glaciers that terminate in the ocean, which causes them to lose a lot of mass at this interface. Debris-covered glaciers refer to glaciers that are covered by sand, rocks, and boulders. Prior work by Rounce has shown that the thickness and distribution of debris cover can have a positive or negative effect on glacial melt rates across an entire region, depending on the debris thickness. In this newest work, he found that accounting for these processes had relatively little impact on the global glacier projections, but substantial differences in mass loss were found when analyzing individual glaciers.
The model is also calibrated with an unprecedented amount of data, including individual mass change observations for every glacier, which provide a more complete and detailed picture of glacier mass change. The use of supercomputers was thus essential to support the application of state-of-the-art calibration methods and the large ensembles of different emissions scenarios.
JOURNAL
Science
New approach to predicting glacier response to climate change shows significant impacts of every temperature increase
In a study that represents “a substantial step forward in predictive modeling” of glacier response to climate change, researchers present predictions for the fate of all Earth’s mountain glaciers, which total more than 215,000 under various policy-relevant climate scenarios. They report that even under the most optimistic scenarios, glaciers globally will lose substantially more mass and contribute to more sea-level rise than current estimates, including those published in the most recent IPCC report, indicate. “[E]very 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,” these authors, led by David Rounce, say. In a related Perspective, Guðfinna Aðalgeirsdóttir and Timothy James reflect on how recent studies have revealed that positive opportunistic framing of climate change is more effective at inciting public support for climate policies than focusing on urgency and consequences. 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.”
Rates of glacier melt have increased over the past few decades, and the continued decline of these vulnerable features will affect sea level rise, freshwater availability for nearly 2 billion people, and risk from glacier-related hazards. Projecting glacier mass loss is critical to future global climate adaptation and mitigation efforts. However, a comprehensive understanding of how Earth’s more than 215,000 individual glaciers (excluding the Greenland and Antarctic ice sheets) will respond under various climate warming scenarios remains challenging. Existing projections are limited to regional scales and neglect key physical processes controlling glacier mass loss. To address these limitations, Rounce and colleagues took advantage of new datasets to produce a set of global glacier projections that explicitly account for glacier dynamics. They produced projections for all of Earth’s individual glaciers under +1.5°Celsius (C), +2°C, +3°C, and +4°C temperature change scenarios by 2100 relative to pre-industrial levels. The findings suggest that glaciers are projected to lose 26±6% to 41±11% of their total mass by 2100, relative to 2015, under temperature increases of 1.5°C to 4°C, respectively. This means that even under the best-case scenarios, where global mean temperature rise is limited to 1.5°C, as many as half of the planet’s glaciers will be lost by 2100. Based on recent climate pledges from COP-26, which project global mean temperature to increase by 2.7°C over the next century, Earth will likely experience a near-complete deglaciation of entire mid-latitude regions, including Central Europe, Western Canada and United States, and New Zealand; this will result in a much greater glacial contribution to sea-level rise than currently estimated.
JOURNAL
Science
ARTICLE TITLE
Global glacier change in the 21st century: Every increase in temperature matters
ARTICLE PUBLICATION DATE
6-Jan-2023
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