A new study that provides a global estimate of rock protection on Earth̵
The Northumbria University study, published in nature Geoscience this week is the first to manually verify the mountain debris on all of the earth’s glaciers.
As glaciers shrink, their surrounding mountain slopes become exposed and eroded rock debris slides down and accumulates on glacier surfaces. This debris forms a protective layer that can be many meters thick, which reduces the rate at which the ice below melts. Although the effects of this protective cover are known, it has never been carefully mapped until now and has therefore not been included in global glacier models.
In addition to revealing where rock debris is located on Earth’s glaciers, the researchers also found and corrected key errors within the Randolph Glacier Inventory – a global inventory of glacier contours on which hundreds of studies are based.
Using Landsat images, the research team from Northumbria University’s Department of Geography and Environmental Science and the Swiss Federal Research Institute WSL spent three years carefully examining and manually verifying more than 923,000 square kilometers of glacier worldwide.
The exercise enabled them to analyze debris protection on a global, regional, as well as individual glacier scale and created the world’s first base data system of glaciers in their current state.
They found that more than 29,000 square kilometers of the world’s mountain glacier area is covered by rock debris – an area equivalent to nearly 500 Manhattan Islands.
Leading researcher Sam Herreid completed the study for his doctoral degree. at Northumbria University and is now believed to be the only person who has examined every glacier on earth, manually corrected the Randolph Glacier Inventory and maintained a level of consistency never before present in a global glacier dataset.
He explained: “The structure of debris protection on each glacier is unique and sensitive to the climate, but until now, global glacier models have omitted debris protection from their forecasts of how glaciers respond to a changing climate.
“We now know that debris covers are found on almost half of the earth’s glaciers, with 7.3% of the world’s total mountain glacier area covered debris.
“When we consider that much of this debris protection is located at the terminal, or toe, of a glacier where the melt would normally be at its highest, this percentage becomes particularly important when it comes to predicting future water resources and sea level rise.”
The study also detected errors within the Randolph Glacier Inventory and found an error rate of 3.3%. One of their findings revealed that 10,000 square kilometers of mapped glacier area was not really glacier, but rather bedrock or vegetation that was either incorrectly mapped earlier or the glacier area that has since melted away.
This, combined with the melt reduction from debris that insulates the ice below, means that all previous global glacier models based on the inventory have probably overestimated the actual volume of glacier melting, runoff and subsequent contributions to global sea levels.
They described 10.6% of the glacier area requiring an updated approach to estimate the melt as “an alarmingly high number” and said their work is an important dataset to revise and likely lower the glacier’s contribution to sea level.
The team also developed a way to analyze how the world’s junky glaciers will evolve in the coming centuries.
By comparing the many glacier states that exist on Earth today, from those considered “young” and icy in Greenland, to “old” and rocks covered in the Himalayas, they were able to put together a conceptual timeline that they believe describes how a glacier can developed in the future.
Their timeline reveals that many glaciers are at the older end of the spectrum and therefore can be considered in decline.
Co-author Francesca Pellicciotti from the Swiss Federal Research Institute WSL and associate professor at Northumbria University, explained: “The upper levels of the glaciers are constantly collecting snow and will always be debris-free, so we only looked at the lower glacier levels where rock debris can accumulate.
“The ice melts and flows away like water, but the rocks do not and accumulate on the surface. Changes in the rate of rock erosion and glacier changes in a warming climate will affect the size and shape of the rock layer at the surface of a glacier at any time.
“Although we can not say exactly what year a glacier will develop into a certain state, say, a state where it is almost completely covered by rocks, we could place each glacier on a conceptual timeline and learn approximately how far along this line each glacier is to be almost completely covered by rocks.
She added: “We found that the majority of glaciers that have debris protection today are beyond a top form of debris protection and are trends closer to the ‘old’ Himalayan glaciers that may no longer exist.
“From a climate change perspective, this is another indication of the toll that a warming climate has on the earth’s glaciers. But we now have a benchmark measurement of debris protection for all the earth’s glaciers and new tools to monitor and predict the degree of change linked to a warming climate.”
The study “The state of rock debris covering the earth’s glaciers” is now available in nature Geoscience.
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Sam Herreid et al. The state of rock debris covering the earth’s glaciers, nature Geoscience (2020). DOI: 10.1038 / s41561-020-0615-0
Provided by Northumbria University
Quote: Quilts with rock waste offer glaciers more protection against climate change than previously known (2020, 5 August) which was retrieved 6 August 2020 from https://phys.org/news/2020-08-blanket-debris-glaciers-climate-previously. HTML
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