Extracting ice from glaciers in the Tropics can be harrowing. The climbs are often dangerous – in the case of Huascarán, avalanches required the team’s mountaineers to create an entirely new route to the summit. (Mountain climbers are known for naming their routes; they christened this one “the Lonnie Thompson route” in Thompson’s honor.) The air gets thinner the higher up a person climbs; high-altitude sickness is a real threat. The symptoms, which include shortness of breath, can also go unnoticed or may begin as low as 8,000 feet. At 22,000 feet, the air is so thin that the scientific team traveled with “backup” oxygen tanks and a Gamow bag, a portable hyperbaric chamber that can be pressurized to sea level values. Fortunately, neither had to be used.

“It’s that high elevation that preserves the record in the ice cores – if you didn't have those cold temperatures, you wouldn't have the record,” Thompson said. “We’ve done dozens and dozens of expeditions, and the result of climate change is that we keep having to go higher on the glaciers. And that becomes an issue, because – well, I’m getting older, for one. And we are strict about acclimatizing – we go up four or five thousand meters on hikes and then come back down and sleep at lower altitudes. But it can wear on your body.”

And Thompson, who celebrated his 71st birthday in Peru at the start of this summer’s expedition, had a heart transplant in 2012.

But the work is necessary, Thompson and the other scientists believe: Because of their ice core work, climate scientists around the world now know that climate change could have devastating effects on vulnerable people in the Andes Mountains and the Tibetan Plateau region. Their research has shown that glaciers in both parts of the world are melting more rapidly than at any point in the past 6,000 years, which could have serious repercussions for the water supply in parts of Peru, Pakistan, China, India and Nepal.

On this most recent trip, they drilled more than 471 meters of glacial ice cores – long columns of ice that had been frozen since the last Ice Age. Work to analyze them is already underway – Thompson calls them “some of the best cores we’ve ever drilled.”

They hope to begin publishing their findings from the cores soon. The cores will be analyzed for mineral dust to detect droughts; isotopes that indicate temperature changes; black carbon and trace elements to determine whether fires like the ones burning in the Amazon this year are part of the historical record; greenhouse gases to see how their concentrations in the atmosphere have changed over time; pollen to track vegetation changes; and microbes to determine how they have evolved over the last 20,000 years.

In the meantime, Thompson and the team are contemplating their next excursion. There are glaciers in Peru and Tibet they would like to revisit, and there are more analyses to be made on ice they’ve already collected from other parts of the world. He wants to be sure he’s helping the next generation of scientists understand how to do this kind of field work.

“These are difficult expeditions – there is the risk of avalanches; there is always the potential for injuries, inflections and various high altitude issues,” he said. “But if you overcome these, you realize the potential of which you’re capable. Some of our younger members just take to it like a duck to water. But the only way they are going to get that experience is to go to the field – first on lower elevation glaciers and then to the higher, more challenging glaciers like those on Huascarán.”