So much ice is melting at the Earth's poles that it's affecting the rotation of the planet, scientists say. Its spin is slowing down slightly, causing days to get longer.

Scientists know a current in the Atlantic Ocean could collapse suddenly as the climate changes. The question of when matters to billions of people around the globe.

An estimated 15 million people are threatened by floods that happen when glaciers melt rapidly. Nepal's Himalayan communities are on the front lines.

Arctic communities have long been plagued by soot that drives snow melt and respiratory disease. Now, humans are making their mark in Antarctica.