Late in the last century scientists published reams of data about Earth’s climate derived from ice cores taken from Greenland and Antarctic. By drilling down into the polar ice with hollow bits, workers were able to pull columns of ice up to the surface. The material brought to light in this way was very special for several reasons.
First, the ice cores show annual layers going back in time. That means scientists can count backwards through time from the surface downward, a bit like school kids counting the rings of a tree.
The ice has tiny bubbles of air in it, air that was trapped in s...