The ice is melting under our feet—literally, not only at the poles but also on the roof of the world, John All says. The Western Washington University environmental science professor and mountain climber calls Earth’s mountain ranges “the world’s water towers”—the source of rivers and much of our weather. And the weather is changing and the ice is melting as American politicians insist that nothing is happening. Icefall is a travelogue through the Himalayas and the jungle mountains of Costa Rica, as well as a call to action. “Knowledge carries an obligation,” he insists. All worries that greenhouse gas might turn Earth into another Venus—a planet unfriendly to “everything we would call life.” And yet, he has hope. “Survival is a pretty good human motivator,” he concludes. Maybe even Donald Trump could understand that?