The ratio of "light" oxygen-16 to "heavy" oxygen-18 in a sample, for instance, reveals the global temperature when the ice formed; it takes colder temperatures for water vapor containing the lighter oxygen isotope to turn into precipitation. Examining the gasses trapped in ice cores is how scientists first learned that the amount of carbon dioxide and the global temperature have been linked at least the last million years of Earth's history.

Osterberg even thinks ice cores will help figure out whether Antarctica's western ice sheet melted 125,000 years ago, the last time Earth's climate warmed to the temperatures the planet is predicted to reach in the next two centuries.

During the summer, the sun’s rays hit the Earth at a steep angle. The light does not spread out as much, thus increasing the amount of energy hitting any given spot. Also, the long daylight hours allow the Earth plenty of time to reach warm temperatures.

During the winter, the sun’s rays hit the Earth at a shallow angle. These rays are more spread out, which minimizes the amount of energy that hits any given spot. Also, the long nights and short days prevent the Earth from warming up. Thus, we have winter!