Mountaintop glacier ice disappearing in tropics around the world

Mountaintop glacier ice in the tropics of all four hemispheres covers significantly less area -- in one case as much as 93% less -- than it did just 50 years ago, a new study has found.

The U.S. National Science Foundation-funded research, published in Global and Planetary Change, found that a glacier near Puncak Jaya, in Papua New Guinea, lost about 93% of its ice over a 38-year period from 1980 to 2018. Between 1986 and 2019 the area covered by glaciers on top of Kilimanjaro in Africa decreased by nearly 75%.

"This research clearly shows that we are dealing with accelerating environmental change," said David Verardo, a program director in NSF's Division of Atmospheric and Geospace Sciences.

The study is the first to combine satellite imagery with data from ice cores drilled during field expeditions on tropical glaciers around the world. The combination shows that climate change is causing these glaciers, which have long been sources of water for nearby communities, to disappear, and indicates that those glaciers have lost ice more quickly in recent years.

The datasets allowed the researchers to quantify exactly how much ice has been lost from glaciers in the tropics. These glaciers are "canaries in the coal mines," said Lonnie Thompson, lead author of the study and a geoscientist at The Ohio State University.

"They are in the most remote parts of our planet -- they're not next to big cities, so you don't have a local pollution effect," Thompson said. "They are sentinels, they're early warning systems for the planet, and they all are saying the same thing."

The study compared changes in the area covered by glaciers in four regions: Kilimanjaro in Tanzania, the Andes in Peru and Bolivia, the Tibetan Plateau and Himalayas of Central and South Asia, and the ice fields in Papua, New Guinea. Thompson has led expeditions to these glaciers and recovered ice cores from each.

The cores are long columns of ice that act as timelines for the region's climate over centuries to millennia. As snow falls on a glacier each year, it is buried and compressed to form ice layers that trap and preserve the chemistry of snow and whatever is in the atmosphere, including pollutants and biological material such as plants and pollen. Researchers can study those layers and determine what was in the air at the time the ice formed.

Glaciers in the tropics respond more quickly to climate change. They exist in the warmest areas of the world, so they can survive only at very high altitudes where the climate is colder. Before Earth's atmosphere warmed, the precipitation there fell as snow. Now, much of it falls as rain that causes the existing ice to melt even faster.