LONDON — The human contribution to melting glaciers is quickening and now accounts for more than two-thirds of the ice lost worldwide, researchers said.
Warming due to greenhouse-gas emissions from burning fossil fuels and destroying forests accounted for about 69 percent of the melt from glaciers in the two decades through 2010, scientists at the University of Innsbruck in Austria said in the journal Science Express. For the period from 1851 through 2010, they calculated the human contribution at a quarter.
"In the 19th and first half of 20th century we observed that glacier mass loss attributable to human activity is hardly noticeable but since then has steadily increased," Ben Marzeion, lead author of the paper, said in a statement Thursday.
The world's glaciers contain enough water to raise sea levels by 41 centimeters (16 inches), according to the United Nations. While that's far less than the 66-meter gain that would result from thawing ice sheets in Greenland and Antarctica, glaciers now contribute more to rising seas than the two polar ice masses because they're disappearing faster.
The findings add to evidence that the climate is warming worldwide, threatening to worsen periods of drought and severe weather in addition to melting glaciers and ice caps. The global average temperature has warmed by about 0.8 degrees Celsius (1.4 degrees Fahrenheit) since 1850, according to the United Nations, which projects temperatures will rise by as much as another 4.8 degrees this century. That would be the quickest shift in the climate since the last ice age ended about 10,000 years ago.
Glacial melt "has been a major cause of sea-level rise during the 20th century," the researchers wrote. As well as affecting seasonal water supplies, glacier retreat "often leads to the destabilization of mountain slopes and the formation of unstably dammed meltwater lakes, increasing the risk of rock slides and catastrophic outburst floods."
Marzeion's team used a computer model and a global inventory of glaciers to analyze changes in their ice content from 1851 through 2010. That enabled them to separate out the human influence on melting rates from natural ice loss due to variability in solar radiance and volcanic eruptions.
"In our data we find unambiguous evidence of anthropogenic contribution to glacier mass loss," Marzeion said.