By Emily Wolfe
Natalie Kehrwald thought she was making a mistake. As a Ph.D. student at Ohio State University in 2008, she had just returned from a 2.5-month expedition collecting ice cores from a glacier at 20,000 feet in Tibet.
To date the ice, Kehrwald was looking for the layers of radioactive isotopes present in glaciers worldwide, deposited during Soviet nuclear testing in 1962-1963 and U.S. testing in 1952-1958.
“If you find those, you have an exact date and an idea of how much snow and ice has accumulated over top of that,” she says.
But Kehrwald couldn’t find the isotopes.
So she analyzed a parallel core, still not finding either radioactive peak. With a colleague, she performed additional tests with the same results. Finally they looked at the uppermost ice and found it dated from the 1940s, which means any accumulation from that time on had melted.
This was the first time anyone had proven that glaciers thin from the top down at such high elevations in the Himalaya, and it had massive implications.