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Half of Earth's glaciers will disappear this century, study finds

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A comprehensive study of all the world’s glaciers outside of Greenland and the Antarctic ice sheets found that nearly half of them will melt by the end of the century, even if the world reaches its most ambitious global warming target.

The study, published Thursday in the journal Science, finds that even with just 1.5 degrees Celsius (2.7 degrees Fahrenheit) warming above pre-industrial levels, about 104,000 of the world’s more than 215,000 mountains glaciers and polar ice caps will melt, raising global sea levels by just under 4 inches.

The twilight of the glaciers of Africa

A 1.5 degree Celsius rise beyond pre-industrial temperatures is now extraordinarily difficult to avoid, suggesting that a change of this magnitude could be nearly unstoppable. With each additional increment of temperature rise, the study found, the outlook gets worse.

Three degrees C (5.4 degrees F) warming, the research found, would translate into a loss of more than 70 percent of global glaciers and result in about 5 inches of global sea level rise. So even if a lot of losses accumulate, the authors say, it’s still worth trying to avoid any warming we can.

“Any reduction in temperature rise will have a substantial impact on sea level rise and glacier loss globally,” said David Rounce, lead author of the study and a researcher at Carnegie Mellon University and the University of Alaska at Fairbanks.

Rounce conducted the survey with an international group of glaciologists affiliated with research institutions in Austria, Canada, France, Norway, Switzerland, Great Britain and the United States.

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The planet has been gradually losing glacial ice since the height of the last great ice age, around 20,000 years ago. But there’s still a lot to give. The greatest amount of remaining ice is concentrated in the Greenland and Antarctic ice sheets, which therefore pose the greatest threat from major sea level rise.

But in the Arctic and Antarctica, as well as in the more temperate latitudes of the planet, many mountainous regions also have numerous glaciers, where thick ice has accumulated because of centuries or even millennia of snow. These glaciers accumulate more ice in winter and often lose some of it in spring and summer, feeding rivers downstream.

Human societies depend on these ice masses for water supply, often heavily, as in the case of thick glaciers in the high mountains of the Hindu Kush-Himalayan region, sometimes called the “third pole” of the planet. Glaciers in this region supply water to massive river systems, including the Indus and Ganges. An estimated 1.9 billion people worldwide depend on glaciers for their water, the research notes.

In many cases, mountain glaciers also have great cultural and tourist importance – an example is the Glacier National Park, in the United States. Glaciers in this part of Montana are in serious trouble, their size and number having plummeted since 1850, according to research and mapping by the US Geological Survey. A 2017 study of the park by the agency showed that the remaining 37 glaciers had shrunk by 68%.

The study released on Thursday concludes that worldwide, this shrinking process, including total loss, will especially affect many of the world’s smallest glaciers, those less than 1 square kilometer (0.39 square miles) in area. .

Larger glaciers and regions with denser glaciers, in the Arctic and Antarctica, will be more resilient as the century progresses and temperatures continue to rise, the research finds, melting and contributing to sea level rise, but not necessarily disappearing.

Alaskan glaciers, for example, are a major contributor to sea level rise. This will continue, but some of the ice deposits are vast enough and in places cold enough to withstand up to 4 degrees C (7.2 degrees F). of heating. But that’s not always true for many smaller glaciers in the mid-latitudes – in regions like the Alps in Europe, Peru Andes and peaks of the South Island of New Zealand.

“Approximately 80% of the world’s glaciers are less than 1 square kilometer,” said Rounce. “They’re very small in terms of area, so when you think about future changes in a warmer climate, they’re very challenged to survive.”

In essence, the new research found that while glacial ice persists at the poles as the planet warms, in temperate and tropical climates mountain ranges, it will be much more difficult. In such places, it is mainly the altitude, rather than the long, dark winters, that protects and preserves the glaciers. And that ice therefore becomes scarcer as warming progresses.

The new study goes beyond previous research by seeking to project the individual fates of all 215,000 or more of the world’s cataloged glaciers and techniques added to explain some of their special attributes. For example, especially at the poles, many glaciers flow far into the sea and even partially float on its surface. This means that they can be melted not only by hot air, but also by warming ocean water.

Meanwhile, in some mountainous areas, some glaciers are covered in dirt and rocky debris – which, if thick enough, can insulate and protect glaciers. But this debris is actually a vulnerability if the layer is thin, because the sun warms the darker surfaces faster than it would with reflective ice.

“Glacier areas around the world are quite varied and have unique responses to climate change,” said Christopher Harig, a glaciologist at the University of Arizona who was not involved in the latest research. “So there’s been a rapid advance in glacier modeling to really capture what’s going on in the different configurations.”

The study suggests a greater overall vulnerability of glaciers than previous work has postulated – especially under lower emissions scenarios consistent with a warming target of 1.5 to 2 degrees Celsius (2.7 to 3.6 degrees Fahrenheit). At these temperatures, the research suggests, glaciers may have an overall 14-23% greater contribution to sea level rise than previous studies have found.

It is part of an all-time pattern of most recent research findings. more intense impacts at lower and lower levels of warming – levels very close to where we are currently.

Paradoxically, however, some experts see hope despite the bad news about the world’s glaciers.

“The good news is that our decisions and actions today will have an impact on ice loss and sea level rise,” said Mathieu Morlighem, a glaciologist at Dartmouth College who was not involved in the study. “Reducing carbon emissions to achieve the Paris agreement [1.5 degrees C goal] is particularly important, as the contribution of glaciers to sea level rises sharply beyond this point. It would also give people and ecosystems more room to adapt.”

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