The Great Spine of Africa expeditions are an unprecedented survey of Africa’s rivers. Biologist Steve Boyes and his team are paddling 40,000 kilometers in dugout canoes to gather groundbreaking data on some of the world’s least-explored waterways.

The first woman to solo ski across Antarctica, Felicity Aston knows better than anyone how to survive on the ice. Now she tells Alex Honnold how her latest expedition unlocked new truths about climate change in the Arctic.