WASHINGTON (AP) - The world’s glaciers are shrinking and disappearing faster than scientists thought, with two-thirds of them projected to melt out of existence by the end of the century at current climate change trends, according to a new study.
But if the world can limit future warming to just a few more tenths of a degree and fulfill international goals — technically possible but unlikely according to many scientists — then slightly less than half the globe’s glaciers will disappear, said the same study. Mostly small but well-known glaciers are marching to extinction, study authors said.
In an also unlikely worst-case scenario of several degrees of warming, 83% of the world’s glaciers would likely disappear by the year 2100, study authors said.
The study in Thursday’s journal Science examined all of the globe’s 215,000 land-based glaciers -- not counting those on ice sheets in Greenland and Antarctica -- in a more comprehensive way than past studies. Scientists then used computer simulations to calculate, using different levels of warming, how many glaciers would disappear, how many trillions of tons of ice would melt, and how much it would contribute to sea level rise.
The world is now on track for a 2.7-degree Celsius (4.9 degrees Fahrenheit) temperature rise since pre-industrial times, which by the year 2100 means losing 32% of the world’s glacier mass, or 48.5 trillion metric tons of ice as well as 68% of the glaciers disappearing. That would increase sea level rise by 4.5 inches (115 millimeters) in addition to seas already getting larger from melting ice sheets and warmer water, said study lead author David Rounce.
“No matter what, we’re going to lose a lot of the glaciers,” Rounce, a glaciologist and engineering professor at Carnegie Mellon University, said. “But we have the ability to make a difference by limiting how many glaciers we lose.”
“For many small glaciers it is too late,” said study co-author Regine Hock, a glaciologist at the University of Alaska Fairbanks and the University of Oslo in Norway. “However, globally our results clearly show that every degree of global temperature matters to keep as much ice as possible locked up in the glaciers.”
Projected ice loss by 2100 ranges from 38.7 trillion metric tons to 64.4 trillion tons, depending on how much the globe warms and how much coal, oil and gas are burned, according to the study.
The study calculates that all that melting ice will add anywhere from 3.5 inches (90 millimeters) in the best case to 6.5 inches (166 millimeters) in the worst case to the world’s sea level, 4% to 14% more than previous projections.
That 4.5 inches of sea level rise from glaciers would mean more than 10 million people around the world — and more than 100,000 people in the United States — would be living below the high tide line, who otherwise would be above it, said sea level rise researcher Ben Strauss, CEO of Climate Central. Twentieth-century sea level rise from climate change added about 4 inches to the surge from 2012 Superstorm Sandy costing about $8 billion in damage just in itself, he said.
Scientists say future sea level rise will be driven more by melting ice sheets than glaciers.