An international study has found that Earth's glaciers will lose 76% of their 2020 mass under current climate policy pledges made by nations.
Those pledges would lead to a global mean temperature 4.9 degrees Fahrenheit above preindustrial levels.
Consequences of the glacier mass loss include a 9-inch sea level rise, changes in biodiversity and increased natural hazards, the research finds.
Alaska, one of 19 glacier regions designated by the international team, would lose 69% of its glacier mass. Of those regions, which don't include the Greenland and Antarctic ice sheets, Alaska has the third-highest glacier mass today, at 16,246 gigatons. Only the Antarctic islands/sub-Antarctic islands and northern Arctic Canada have more glacier mass.
Limiting the planet's warming to 2.7 degrees Fahrenheit — the low-end target of the 2015 Paris Agreement — would reduce global mass loss to 47%, according to the study. Alaska's loss would drop to 41%, according to the researchers.
Professor Regine Hock of the University of Alaska Fairbanks Geophysical Institute and the University of Oslo is among the co-authors.
The research was published today in Science .
"This is the whole point: When you stop climate change, glaciers don't stop losing mass," Hock said. "Glaciers have a memory. They continue losing mass for tens, hundreds or even thousands of years until they retreat to high elevations where it's colder."
The new research is a break from previous studies, which calculated glacier mass loss in various scenarios from preindustrial times only through 2100. The new research has no artificial end date for mass loss; rather, it calculates mass loss at a glacier's projected time of reaching equilibrium, the point at which seasonal variation results in no net change in ice loss. Glaciers gain mass in colder months and lose mass in warmer months.
Alaska glaciers would reach equilibrium on average in about 330 years under the 2.7-degree increase of the Paris Agreement, the researchers determined.
Hock is also co-chair of the Glacier Model Intercomparison Project, an international initiative that compares global and regional glacier models to improve projections of glacier mass change and sea-level rise. The goal is to improve confidence in glacier response predictions under future climate conditions.
"This is not a single study by one researcher; it's an internationally coordinated effort," Hock said. "It was four years and brought together the entire community to work on global glacier modeling."
The team of 21 scientists from 10 countries used eight glacier models to calculate the potential ice loss of the more than 200,000 glaciers outside of the Greenland and Antarctic ice sheets under a wide range of global temperature scenarios relative to 2020. For each scenario, they assumed that temperatures would remain constant for thousands of years.
Alaska, even under current climate conditions of 2.1 degrees Fahrenheit above preindustrial levels, would lose 37% of its glacier mass, the study finds. Ice loss rises under greater temperature increases: 41% lost at 2.7 degrees, 58% at 3.6 degrees, 69% at 4.9 degrees, 71% at 5.4 degrees and 80% at 7.2 degrees.
The 2.7- and 3.6-degree increases are the Paris Agreement's lower and upper targets. The 4.9-degree projection is the current trajectory based on climate pledges made to date toward the agreement's goal. The 5.4- and 7.2-degree projections were determined by the study's authors.
Overall, the planet would lose 39%, 47%, 63%, 76%, 77% and 86% of its glacier mass under those temperature increases.
The two lead authors emphasize that action is needed to reduce glacier loss.
"Our study makes it painfully clear that every fraction of a degree matters," says co-lead author Harry Zekollari from the Vrije Universiteit Brussel in Belgium. "The choices we make today will resonate for centuries, determining how much of our glaciers can be preserved."
"Glaciers are good indicators of climate change because their retreat allows us to see with our own eyes how climate is changing," said co-lead author Lilian Schuster from the University of Innsbruck.
"However, since they adjust over longer timescales, their current size vastly understates the magnitude of climate change that has already happened," she said. "The situation for glaciers is actually far worse than visible in the mountains today."
The research was conducted as part of the Glacier Model Intercomparison Project and coordinated by the Climate and Cryosphere Project of the World Climate Research Programme. This year is the United Nations International Year of Glaciers' Preservation.
