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Since 1958 scientist Charles Keeling and others have measured the amount of carbon dioxide in the atmosphere in Hawaii. The yearly fluctuations in carbon dioxide are due to seasonal plant growth, while the overall rise in carbon dioxide over many years is due to a combination of fossil fuel burning, deforestation, and cement production.
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Windows to the Universe based on data from NOAA and UCSD

The Carbon Cycle Changes

Today, the carbon cycle is changing. Humans are moving more carbon into the atmosphere from other parts of the Earth system. More carbon is moving to the atmosphere when fossil fuels, like coal and oil, are burned. More carbon is moving to the atmosphere as humans get rid of forests by burning the trees. Burning wood releases carbon into the atmosphere that had been stored in the tree.

Most of the carbon in the atmosphere is in molecules of carbon dioxide (CO2). Carbon dioxide is a greenhouse gas; it causes heat to be retained in the atmosphere. By increasing the amount of this greenhouse gas in the atmosphere, Earth is becoming warmer.

Carbon dioxide spends a long time, up to many centuries, in the atmosphere, so even if people stopped adding carbon dioxide to the atmosphere now, Earth would continue to warm. The carbon can slowly move back into the biosphere, taken up by plants as they photosynthesize. It can also move into the oceans. And it can be stored in rocks of the geosphere like limestone. Researchers are currently studying these processes and others that move carbon out of the atmosphere.

The carbon cycle has changed throughout the billions of years of Earth’s history. However, prehistoric changes happened for different reasons. The amount of carbon dioxide in Earth’s atmosphere increased at times in the past, during the Devonian period of the Paleozoic for example, because of volcanic eruptions. Volcanoes release more than lava and ash. They also send gases, like carbon dioxide into the atmosphere. Today the amount of volcanic eruptions is very small compared with other times in the past, yet the concentration of carbon dioxide in the atmosphere is quite high because people are burning forests and fossil fuels.

Last modified October 26, 2007 by Lisa Gardiner.

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