As the Earth's climate shifts, the vast, ancient ice sheets of Greenland and Antarctica are beginning to show signs of instability. Scientists are racing to understand the complex, interconnected forces driving this change, from the warming of ocean currents to the subtle, rhythmic variations in the planet's rotation. Through a combination of satellite monitoring, radar flights, and deep-ice drilling, researchers are piecing together the history of our planet's climate to predict what the future may hold for the world's frozen regions and the global sea levels that depend on them.