Changing carbon: Ice cores and proxies

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Scientists have made direct measurements of atmospheric carbon dioxide (CO2) levels for over 50 years. In addition to this, scientists investigate earlier CO2 levels by collecting samples of air trapped in ice cores extracted from the Antarctic ice sheet and from suitable glaciers around the world. The ice core data show that the concentration of CO2 in the atmosphere is higher today than it’s been for at least 800,000 years, and the rate of increase has been 100 times faster than any previous change in the ice core record. Other scientists use ‘proxies’, such as ancient sediments and leaf or plankton fossils, to estimate CO2 levels in even earlier periods.