The retreat of glaciers in the Canadian Arctic caused by a warming climate has revealed landscapes that haven’t been ice-free in more than 40,000 years, according to a new study by researchers at the University of Colorado Boulder.

The study, published Jan. 25 in the journal Nature Communications, used radiocarbon dating to determine the ages of plants collected at the edges of 30 retreating ice caps on Baffin Island, west of Greenland.

That dating suggested those locations were continuously ice-covered for at least 40,000 years, Gifford Miller, senior author of the research and a professor...