Scientists can measure concentrations of two greenhouse gases—carbon dioxide
and methane—trapped within air bubbles in the ice. This can help tell them how
long the greenhouse effect has been around and help them predict how much may
be part of natural cycles versus effects produced induced by humans. Scientists
can also measure hydrogen peroxide in ice cores taken from locations with
distinct seasons to determine where the annual layers are. Hydrogen peroxide is
created by a chemical reaction that requires ultraviolet light—the higher the
concentration of hydrogen peroxide, the more likely the layer was formed in
summer when there is more light. The tephra (volcanic ash) and sulfate in the ice allow
reconstruction of the earth's volcanic history long before humans were around to observe and
document eruptions. At low latitudes these layers can also preserve pollen, organic matter,
and even insects!
