The steady melt of glacial ice around the world is largely due to man-made factors, such as greenhouse-gas emissions and aerosols, a new study finds.
Humans have caused roughly a quarter of the globe's glacial loss between 1851 and 2010, and about 69 percent of glacial melting between 1991 and 2010, the study suggests.
"In a sense, we got a confirmation that by now, it is really mostly humans that are responsible for the melting glaciers," said lead researcher Ben Marzeion, an associate professor of meteorology and geophysics at the University of Innsbruck in Austria. [Images of Melt: See Earth's Vanishing Ice]
Vanishing glaciers are often associated with global warming, and other studies have estimated past ice loss and made projections of future melt. But until now, researchers were unsure how much glacial loss was tied to human factors.
"So far, it has been unclear how much of the observed mass losses are caused by humans rather than natural climate variations," Regine Hock, a professor of geophysics at the University of Alaska Fairbanks who was not involved in the study, wrote an in email to Live Science.
The researchers used "state-of-the art modeling techniques," in their work, Hock said.
The research team relied on 12 climate models, most of them from the latest reports from the Intergovernmental Panel on Climate Change, an international group of climate-change experts convened by the United Nations. By combining the models, along with data from the Randolph Glacier Inventory (a catalog of nearly 200,000 glaciers), the researchers created a computer model that included only natural contributions to glacier melt, such as volcanic eruptions and solar variability, and another model with both human and natural factors.
Using data from 1851 to 2010, the researchers compared the two models with real measurements of glaciers to determine which one better represented reality. The study did not include glaciers in Antarctica, because not enough data on the region was available during the 159 years covered by the study.
The model with the man-made influences was a better fit, they found.