Climate Change 40 40.4 Evidence of a changing atmosphere
Ice core data Ice cores are cylinders of ice drilled out of an ice sheet or glacier. Most ice core records come from Antarctica and Greenland, and the longest ice cores extend to 3 km in depth. The oldest continuous ice core records so far are believed to give us data from 123,000 years
ago in Greenland and 800,000 years ago in Antarctica. One method of dating ice cores is to count the layers in the ice. The section shown in Fig. 13 contains 11 annual layers with summer layers (arrowed) sandwiched between darker winter layers. The ice contains small bubbles of air which are samples of the atmosphere from the time they were trapped. Scientists can use carbon dating on the carbon dioxide in these air bubbles. This allows the ice to be dated. Ice cores contain information about past temperatures
and about many other aspects of the environment, such as volcanic activity. It is possible to measure the past concentration of
gases (including carbon dioxide and methane) in the atmosphere from these bubbles.
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Fig. 13 Ice is laid down in layers, with winter layers showing dark beside the light-coloured summer layers.
Research on ice cores shows that: Atmospheric carbon dioxide levels are now 40% higher than before the Industrial Revolution. This increase is thought to be due to burning fossil fuels and deforestation. There has been a huge increase in the amount of methane in the atmosphere over the last two centuries. This is thought to be due to intensive livestock farming, rice paddies and landfill.
Atmospheric CO2 (Hawaii)
Carbon dating Matter that
contains carbon can be dated by measuring the amount of carbon 14 it contains.
