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The Carbon Cycle and Climate Warming

"The Carbon Cycle and Climate Warming"

Journal article

By: Richard A. Kerr

Date: December 9, 1983

Source: Kerr, Richard A. "The Carbon Cycle and Climate Warming: Learning How Carbon Cycles through the Environment, With and Without Human Intervention, Is Crucial to Predicting the Greenhouse Effect." Science 222 (1983): 1107-1108.

About the Author: Richard A. Kerr has been a staff journalist with Science magazine since 1977. He has a Ph.D. in chemical oceanography and reports on earth science, planetary science, and paleontology subjects.


The greenhouse effect refers to a process in which gases in the atmosphere allow solar radiation to penetrate to the earth's surface, while also reabsorbing radiation as it attempts to exit the atmosphere. The result of the greenhouse effect is the trapping of heat in the atmosphere. In turn, this causes an increase in temperature. The increase in the earth's temperature over time is generally referred to as global warming or climate warming.

There are various greenhouse gases that have this effect. These include water vapor, methane, and chlorofluorocarbons. However, one of the most important of greenhouse gases is carbon dioxide (CO2), for several reasons. Carbon dioxide is responsible for approximately half of the heat retained by the atmosphere and is especially important because it is the atmospheric gas that is increasing at the fastest rate. Carbon dioxide is produced mainly by the burning of fossil fuels and by deforestation, both of which have been increasing since industrialization. This has led to a continuing increase in the amount of carbon dioxide being released into the atmosphere. Finally, processes that have caused the increased levels of carbon dioxide have not stopped and are not likely to in the future. In fact, the burning of fossil fuels is expected to increase over time. This makes understanding the impact of increased carbon dioxide levels an important environmental issue.


[This text has been suppressed due to author restrictions]

[This text has been suppressed due to author restrictions]


Scientists accept that increasing levels of carbon dioxide will cause an increase in global temperature. However, they are not able to easily predict the extent of the impact on the Earth's atmospheric temperature. The difficulty occurs because the level of carbon dioxide released into the atmosphere does not equal the level that remains in the atmosphere. This occurs because carbon dioxide exists as part of the carbon cycle.

The carbon cycle is a complex system that describes the forms that carbon takes. In the atmosphere, carbon exists as carbon dioxide gas. The carbon dioxide becomes part of the biosphere when organisms convert it to biological carbon via photosynthesis. Carbon dioxide becomes part of the hydrosphere when it is dissolved in ocean water. These two processes remove carbon dioxide from the atmosphere as it is being added. The question that remains unanswered is how much carbon dioxide is removed from the atmosphere. The ongoing rise in carbon dioxide levels in the atmosphere suggests that not all of the carbon dioxide added is removed by the carbon cycle. However, the balance that occurs is not known.

This creates a problem in predicting the impact of carbon dioxide greenhouse gases on global warming. This is further complicated because it is not known how much carbon dioxide will be released in the future. Kerr describes how carbon dioxide emissions are expected to increase. However, these predictions are far from being certain.

The next problem identified by Kerr is based on determining how carbon dioxide emissions since the industrial age have influenced atmospheric carbon dioxide levels. To understand this, scientists must first know what the concentration of atmospheric carbon dioxide was before it began to be inflated by industrialization. In completing this analysis, they found that the global warming that has already been observed cannot be explained only by industrialization—the carbon dioxide levels have increased more than the burning of fossil fuels accounts for.

This suggests that there is another source of atmospheric carbon dioxide. Kerr describes how this source is most likely to be the biosphere, where deforestation and cultivation both cause carbon that exists as part of the biosphere to be released into the atmosphere. At the same time, another issue complicates the matter, which is that the ocean is thought to have removed a lot of the carbon dioxide from the atmosphere. This means that the amount of carbon dioxide released since industrialization must have been even greater.

While Kerr does not provide any final answers that make it possible to understand the rise in carbon dioxide levels, he makes it clear that understanding global warming and greenhouse gases requires an understanding of the carbon cycle. Without this, scientists are not able to determine past levels of atmospheric carbon dioxide or understand how future levels will change. This shows that understanding the carbon cycle is crucial to being able to predict the impact of the burning of fossil fuels and deforestation and ultimately, understanding and predicting global warming.



Drake, Frances. Global Warming: The Science of Climate Change. New York: Oxford University Press, 2000.

Harvey, Danny. Global Warming: The Hard Science. New York: Prentice Hall, 2000.

Houghton, John. Global Warming: The Complete Briefing. New York: Cambridge University Press, 1997.


Joos, F., G. Plattner, T. F. Stocker, O. Marchal, and A. Schmittner. "Global Warming and Marine Carbon Cycle Feedbacks on Future Atmospheric CO2." Science 284 (1999): 464-467.

Kerr, Richard A. "It's Official: Humans Are Behind Most of Global Warming." Science 296 (2001): 566.

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