Gwenn Flowers, a glaciologist, trudges back and forth across a vast glacier in southwest Yukon, pulling a radar device mounted on skis behind her. "We as Canadians are stewards of about a third of the world's mountain glaciers and ice caps, so this is our responsibility," Flowers says. The dramatic changes to the glaciers in the Yukon are an early warning of what climate change could mean for the rest of the planet, researchers say. And Flowers sees lots of reason for concern reflected in the state of the ice.