A comprehensive study of all the world's glaciers other than the Greenland and Antarctic ice sheets shows that over half of them will melt by the end of the century, even if the world fulfills its most aggressive global warming target.

The study, published Thursday in the journal Science, discovered that even with only 1.5 °C (2.7 degrees Fahrenheit) of warming above preindustrial levels, 104,000 of the world's more than 215,000 mountain glaciers and ice caps will melt, raising global sea levels by just under 4 inches.

A 1.5°C increase above preindustrial temperatures is currently extremely difficult to avert, implying that such a development may be nearly unstoppable. The outlook worsens with each extra degree of temperature rise.

According to the study, 3°C (5.4 degrees Fahrenheit) of warming would result in the disappearance of more than 70% of the world's glaciers and a 5-inch rise in global sea level. Even though many losses are already baked in, the authors argue that it is still worthwhile to attempt to avert as much warming as possible.

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

Rounce collaborated with an international team of glaciologists from Austria, Canada, France, Norway, Switzerland, the United Kingdom, and the United States on the study.

Since the end of the last major ice age 20,000 years ago, the earth has been progressively losing glacial ice. However, there is still much to contribute. The majority of remaining ice is concentrated in Greenland and Antarctica's ice sheets, which offer the greatest threat of major sea-level rise.

However, many high mountain locations in the Arctic and Antarctic, as well as in the planet's more temperate latitudes, have numerous glaciers, where thick ice has accumulated due to centuries or even millennia of snowfall.

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These glaciers then gather more ice during the winter and frequently lose some of it during the spring and summer, supplying rivers downstream.

Human communities rely largely on these ice masses for water supplies, like in the case of the vast glaciers of the Hindu Kush-Himalayan region, sometimes referred to as the planet's "third pole". This region's glaciers feed water into enormous river systems such as the Indus and Ganges. According to the study, glaciers provide water to an estimated 1.9 billion people globally.

According to the study, this process of shrinkage, up to and including total loss, will disproportionately affect many of the world's smaller glaciers, those less than 1 square kilometer (0.39 square miles) in area.

The current study goes beyond previous studies by attempting to forecast the individual fates of all 215,000 or more of the world's recorded glaciers, as well as adding methodologies to account for some of their unique characteristics. 

Many glaciers, for example, flow far forth into the sea and even partially float on the surface, particularly near the poles. This means that they can be melted by both warm air and warm ocean water.

The study implies that glaciers are more vulnerable than previously thought, particularly at lower emissions scenarios fit with a 1.5 to 2°C warming goal (2.7 to 3.6 degrees Fahrenheit). The research implies that at these temperatures, glaciers could contribute 14 to 23% more to sea level rise than previous studies revealed.

It's part of a trend in which newer research finds increasingly more dramatic effects at ever-lower levels of warming - levels very near to where we are now.

Despite the grim news concerning the world's glaciers, some researchers see the reason for optimism.

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