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

Carbon moves naturally to and from various parts of the Earth. This is called the carbon cycle. Today, however, scientists have found that more carbon is moving into the atmosphere from other parts of the Earth. It moves into the atmosphere when fossil fuels, like coal and oil, are burned. It moves into the atmosphere when forests burn.

The carbon in the atmosphere is in molecules of carbon dioxide (CO2). Carbon dioxide is a greenhouse gas. Greenhouse gases trap heat in the atmosphere. By increasing the amount of carbon dioxide in the atmosphere, Earth is becoming warmer.

Even if people stopped adding carbon dioxide to the atmosphere now, Earth would continue to warm for a long time. Carbon dioxide does not leave the atmosphere quickly; it can spend many centuries up there. Over time, carbon can move slowly out of the atmosphere and into plants. The plants take the carbon dioxide out of the atmosphere as they make their food from the Sunís energy by photosynthesis. Carbon can also move into ocean water or be stored in rocks. We are currently adding carbon to the atmosphere faster than all the plants on Earth can take it out. Scientists are studying ways to move some of the carbon out of the atmosphere.

This isnít the first time that there have been high amounts of carbon dioxide in the Earthís atmosphere. The carbon cycle has changed throughout the billions of years of Earthís history. However, prehistoric changes happened for different reasons. During the Paleozoic, tons of volcanic eruptions spewed lava, ash, and gases like carbon dioxide into the atmosphere. The lava fell to the ground right away. Most of the ash fell to the ground within a few days to weeks. But the carbon dioxide stayed in the atmosphere for hundreds of years! Today, the amount of volcanic eruptions is very low compared with other times in the past, yet the amount of carbon dioxide in the atmosphere is high because of burning forests and fossil fuels.
Last modified October 26, 2007 by Lisa Gardiner.

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