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The world’s glaciers may contain less water than previously believed, a new study has suggested, for the millions of people around the world who depend on glacier melt for drinking water, crop irrigation and daily use, and freshwater supplies may peak sooner than expected.

The latest findings are based on satellite images taken in 2017 and 2018. These are a snapshot of time; scientists will need to work harder to correlate them with long-term trends. But they imply that further global warming could cause today’s ice to disappear in many places faster than previously thought.

In the tropical Andes, for example, the study estimates glacial volume is 27 percent less than the scientific consensus a few years ago. The study found that glacier volume was 35 percent smaller in parts of Russia and northern Asia.

Worldwide, the study found 11 percent less ice in glaciers than previously estimated. But he found 37 percent more ice in the high mountains of Asia, and 10 percent more in Patagonia and central Andes.

Romain Millan, a geophysicist at the Institute for Environmental Geosciences in Grenoble, France, said the new estimates come from a more detailed and realistic digital reconstruction of Earth’s 215,000 glaciers than previously possible. studyIt was published Monday in the journal Nature Geoscience.

Despite this, “we still have a lot of uncertainty in some areas,” said Dr. Mostly because of the paucity of on-site measurements that help inform any digital restructuring, Millan said. These regions, including the Andes and the Himalayas, are “areas where people rely on fresh water from glaciers,” he said.

Melting glaciers are threatening livelihoods and reshaping landscapes in North America, Europe, New Zealand and many places in between.

In the upper Indus basin of the Himalayas, which connects Afghanistan, China, India and Pakistan, glacial melt accounts for almost half of the river flow. Anjal Prakash, a water expert at the Indian School of Business in Hyderabad who did not work on the new study, said the logistical and political challenges mean that scientists can only monitor a small fraction of the Himalayan glaciers.

Dr. “It’s a data-deficient region,” Prakash said. “Countries do not cooperate. They don’t share information with each other.”

While 1.5 billion people benefit from the waters and other resources of the Himalayas, they also face increased risks. heavy floodThe area is “just waiting for a disaster to happen,” said Dr. Prakash.

As the glaciers melted, they contributed to rising global sea levels. The new study shows that together they could add 10 inches to the oceans instead of the previously estimated feet. Either way, that’s small compared to what the melting of Greenland and Antarctica could add to sea levels in the distant future if the planet warms to catastrophic levels.

Dr. Millan and colleagues combined more than 811,000 satellite images to measure the speed at which glaciers’ surfaces are moving to produce their new estimate of glacier sizes. Glaciers may seem like solid, unchanging masses, but they are actually in constant motion: they slide across the terrain; deformed under its own weight; flowing, like syrup, down the valleys. This move is a clue to the amount of ice locked inside.

“The thickness of the glacier controls how fast it moves,” said Daniel Farinotti, a glaciologist at the Swiss University of ETH Zurich, who was not working on the new study. “And so, conversely, if you know how fast it’s moving, you can say something about thickness.”

The high resolution of satellite imagery, Dr. It allowed Millan and his colleagues to capture subtle changes in the thickness of glaciers, such as narrow grooves in the underlying ground. They can map small glaciers that have never been mapped before in South America, Europe, and New Zealand.

Mathieu Morlighem, an geoscientist at Dartmouth College who worked on the new study, said scientists understand less about some of the glaciers that cover the world’s mountains than they do about the much larger ice sheets of Greenland and Antarctica.

It has been measured at only a few thousand glacier sites worldwide. In places like North America, the milder climate means more pockets of water in the glaciers, which could obscure radar measurements. Dr. Compared to giant ice sheets, where fast-moving ice flattens underlying bedrock over time, the terrain beneath mountain glaciers can be “very complex”, making their size difficult to measure, Morlighem said.

“Only 10, 15 years ago we barely knew the area of ​​the glaciers,” said Regine Hock, a geoscientist at the University of Oslo in Norway who was not involved in the new study. Estimates of glacial volume were “very, very rough”.

Dr. Today’s “data revolution” is helping them make better predictions about local and regional water resources, even though the big picture on a global scale — that glaciers will thin significantly this century — is unlikely to change much, Hock said. “There’s just too much ice,” he said, “and then it’s gone.”