The world's glaciers are shrinking and disappearing faster than scientists thought, with half of the Earth's glaciers, notably smaller ones, destined to disappear by the end of the century and if current climate change trends are left unaltered that number could rise to over 80% of them, according to a new study.
The findings, published in the journal Science on Thursday, provide the most comprehensive look so far at the future of the world's 215,000 glaciers.
The authors emphasized the importance of restricting greenhouse gas emissions to limit the consequences from glacier melt such as sea level rise and depletion of water resources.
To help orient policymakers, the study looked at the impact of four scenarios on glaciers, where global mean temperature change is 1.5 degrees Celsius (2.7 degrees Fahrenheit), 2.0 degrees Celsius, 3.0 degrees Celsius and 4.0 degrees Celsius.
"Every degree increase produces more melt and loss," said Regine Hock of the University of Oslo and University of Alaska Fairbanks, a co-author of the study.
"But that also means if you reduce the temperature increase, you can also reduce that mass loss," Hock told Agence France-Presse (AFP). "So in that sense, there is also a little bit of hope."
Even if global temperature rise is limited to 1.5 degrees Celsius above pre-industrial levels – the most ambitious goal of the Paris Agreement – the researchers estimated that 49% of the world's glaciers would vanish by the year 2100.
That would represent about 26% of the world's glacier mass because the smallest glaciers would be those first impacted.
The global mean temperature is currently estimated to be increasing by 2.7 degrees Celsius which would cause a near-complete loss of glaciers in Central Europe, Western Canada and the continental United States and New Zealand.
"Regions with relatively little ice like the European Alps, the Caucasus, the Andes, or the western United States, they lose almost all the ice by the end of the century almost no matter what the emission scenario is," Hock said. "So those glaciers, they're more or less doomed."
Under the worst-case scenario – a global temperature rise of 4.0 degrees Celsius – giant glaciers such as those in Alaska would be more affected and 83% of glaciers would disappear by the end of the century.
Glacier loss would also exacerbate sea level rise.
"The glaciers that we are studying are only one percent of all ice on Earth," said Hock, "much less than the Greenland ice sheet and the Antarctic ice sheet. But they have contributed to sea level rise almost just as much as Greenland and Antarctic ice sheet together in the last three decades," she said.
Warming of 1.5 degrees Celsius would lead to an increase in average sea levels of nine centimeters while temperatures 4.0 degrees Celsius higher would cause 15 centimeters (5.9 inches) of sea level rise.
"It doesn't sound very much, nine centimeters up to 15 centimeters," Hock said, "but it's not global sea level that is that much of a concern. It's mostly associated storm surges," she said, which have the potential to cause "a lot more damage."
The disappearance of glaciers will also impact water resources because they provide fresh water for some two billion people.
"The glaciers compensate for losing water in summer when it's not raining much and it's hot," Hock said.
The study's projections, which are more pessimistic than those of United Nations climate experts, were reached through observations of the mass of each glacier through the decades and computer simulations.
Despite the alarming findings, Hock said "it is possible to reduce the mass loss by human action. If it happens is of course a different question," she said. "If that happens is of course up to the policymakers."
