"Glaciers thin and retreat around the world as a result of rising air temperature, but the glaciers don't care whether or not the increase in temperature is due to natural or human causes," Hock said. "Over the last 150 years, most of the mass loss was due to natural climate variability, caused, for example, by volcanic eruptions or changes in solar activity.
"However, during the last 20 years, almost 70 percent of the glacier mass changes were caused by climate change due to humans," she wrote.
Interestingly, the study found that glaciers, which are slow to react to climate change, are still recovering from the end of the Little Ice Age that lasted from the 14th to the 19th centuries. During the Little Ice Age, temperatures were about 1.8 degrees Fahrenheit (1 degree Celsius) colder than they are today.
Warmer temperatures after the Little Ice Age affected the glaciers. "Essentially, what we find is that glaciers would be melting without any human influence," Marzeion told Live Science.
The melt, however, would not be happening as quickly as it is today if it weren't for man-made contributions, such as aerosols from wood or coal fires, he said. Aerosols are particles suspended in the atmosphere that absorb and scatter the sun's radiation.
Even if climate change from both man-made and natural causes stopped today, the glaciers would continue to melt and are projected to raise ocean levels by 2.7 inches (7 centimeters) during this century, Marzeion said.
As global temperatures continue to rise, the glaciers will continue to disappear. The melt may provide more water for irrigation and other needs, but it won't be sustainable because the glaciers may eventually vanish, Marzeion said. In the meantime, people can try to reduce man-made contributions to global warming and adapt to the changing planet, he said.
The study was published online today (Aug. 14) in the journal Science.
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