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Mountain glaciers may hold less ice than previously thought – here’s what that means for 2 billion downstream water users and sea level rise

Mountain glaciers may hold less ice than previously thought – here’s what that means for 2 billion downstream water users and sea level rise

A herder moves sheep down a road next to a large water pipe with mountains in the background.

Nearly a quarter of the world’s population relies on mountain glaciers for their water supply. But figuring out just how much ice they hold – and how much water will be available as glaciers shrink in a warming world – has been notoriously difficult.

Scientists have mapped the speed and movement of more than 200,000 glaciers in a new study to find out why. They found that glacier volume estimates are widely used. You may get a discount of around 20% in terms of how much Earth’s glaciers outside the Greenland and Antarctic ice sheets could contribute to sea level rise.

Mathieu MorlighemCoauthor of the study and a leader in icesheet modeling, he explains why The new results hold a warning for regions that rely on glaciers’ seasonal meltwater, but barely register in the big picture of rising seas.

1) What does it mean for those who depend on mountain glaciers for water if they hold less ice than previously thought?

Globally, Nearly 2 Billion peopleAs their main source of water, mountain glaciers and snowpack are important. Many also rely upon glacier water for agriculture or hydropower generation, particularly during the dry season. The vast majority of glaciers worldwide are losing more mass each year due to climate change. They are slowly disappearing. That will. These populations are greatly affected.

These communities must know how long their glaciers are expected to continue to provide water, and what to do if they disappear in order to be prepared.

We found significantly lower total volumes of ice in most locations than previously estimated.

For example, in the tropical Andes (from Venezuela to northern Chile), we found that glaciers had 23% less ice then previously believed. This means that downstream communities have less time to adapt to climate changes than they may have anticipated.

A herder moves sheep down a road next to a large water pipe with mountains in the background.
A herder walks along a water pipe near La Paz in Bolivia. The glacier that was once relied upon for water is almost gone.
Tim Clayton/Corbis via Getty Images

Even in the Alps where scientists have a lot more direct ice thickness measurements, it was found that glaciers could have 8% less than previously thought.

The Himalayas are the exception. We found that these mountains could have 37% more glaciers than previously estimated. This saves communities who depend on these glaciers some time, but it doesn’t change the fact that they are melting with global warming.

These new estimates should be considered by policymakers to help them revise their plans. Although we don’t make any predictions about the future, this study does give us some indications. a better descriptionImagine what the glaciers and their water supply look like today.

2) How does this affect future sea-level rise estimates?

First, it’s important to understand that melting glaciers are only one contributor to sea level rise as the climate warms. About one-third of today’s sea level rise is due to Thermal expansion of the ocean – as the ocean warms, water expands and takes up more space. The remaining two-thirds are from Mountain glaciers and ice sheet shrinkage.

We found that all the glaciers (not including the huge ice sheets in Greenland or Antarctica) would melt completely. Sea level would rise by approximately 10 inchesInstead of 13 inches. This may seem like a huge difference, given the ocean’s size, but it is worth considering. The Antarctic ice sheet could be completely disintegrated. 190 feetSea level and the Greenland glacier would help 24 feet.

The 3 inches we are referring to in this study don’t question current projections of sea-level rise.

3) What is your study that showed how to determine the volume of ice in glaciers?

It is possible to be surprised at how little we know about the basic characteristics of mountain glaciers.

Satellites have changed our understanding of glaciers, since the 1970s. Locations and surface areas of glaciers. But satellites cannot see “through” the ice. In fact, for 99% of the world’s glaciers, there is no direct measurement of ice thickness. Scientists have spent more time mapping them. Greenland and Antarctica Ice SheetsWe have more detailed volume measurements for the terrain and the area below. NASA, for instance, has dedicated an entire airborne mission. Operation IceBridgeTo measure the thickness of ice in Greenland or Antarctica, click here

The new mapping techniques are more precise, as a comparison of Iceland’s Vatnajökull ice cap shows. The new map can be seen in the image below.
R. Millan et al., 2022

Scientists have created various techniquesTo Determine the volumeDespite the fact that glaciers are plentiful, there has been a lot of uncertainty about mountain glaciers.

We did something new compared to other studies. We used satellite imagery to map the glaciers’ speed. Glacier ice behaves like thick syrup when it is thick enough. Two satellite images are used to measure how far the glacier ice is moving. We can also map its speed, which ranges from a few hundred feet to a mile per year. It was not an easy task to map the displacement of more then 200,000 glaciers, but it created a data set that no one had ever seen before.

Images show the velocity glacier ice across the globe.
R. Millan et al., 2022

This new information about ice speed and simple principles for ice deformation was used to determine the thickness at each pixel in these satellite images. The ice sliding on its surface and its internal deformation are the main causes of the observed ice speed from space. The internal deformation of the ice depends on its surface slope, ice thickness, and its slipperiness on its bed is dependent on the temperature at its base, liquid water presence, and the nature and composition of the sediments and rocks beneath. Once we had established a relationship between ice speed, sliding, and ice thickness, we could calculate it.

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800,000 pairs were analyzed by satellites from NASA and European Space Agency to determine the flow speed for all these glaciers.

As with any indirect method, these estimates are not perfect and will improve as more data is collected. We have made great strides in reducing uncertainty.

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