What do the air bubbles in the Earth's polar ice caps reveal?

Answer: The composition of air as it was thousands of years ago.

Water dissolves air. When water freezes its dissolved air forms tiny bubbles. That's why ice cubes look "cloudy." The cloudiness is due to tiny bubbles. The ice in a hockey rink has tiny air bubbles in it, making it look a bit cloudy and not very transparent to the makings below the ice on the rink floor, such as the red line, the blue lines, the goal area, etc.

To make clear ice water must first be boiled to expel air. Then the air-free water is frozen without contact with air. Some restaurants have machines that make clear ice cubes for use in beverages.

Ice at the North Pole has accumulated over thousands of years. Each winter snow falls to create a new layer of snow. The layers compress into ice as time goes by. The layers are visible as bands in the ice, so counting the number of bands with depth in the ice gives the age of ancient ice.

Ice at the North Pole has been studied by scientists. Cores are drilled into the ice going down over a mile in depth. Samples of the ice cores so obtained are heated to expel the trapped air. The air is then analyzed as to content of carbon dioxide and other gases. These studies show the composition of the Earth's atmosphere as it was going as far back as 400,000 years ago.

The studies show that the Earth has had periods of tropical climates and winter climates lasting thousands of years. The reasons for these changes are being studied. Some suggestions are: Changes in the Earth's orbit, changes in the Sun's light output, and carbon dioxide changes due to plant life, or due to volcanoes.

The burning of fossil fuels has only occurred during the latest 200 years. This man-made pollution is believed to be speeding-up the natural causes of "climate warming."