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Carbon Cycle On Assignment

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Carbon Cycle
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Carbon Cycle Feature Image
   
By Tim AppenzellerPhotographs by Peter Essick



Hooked on fossil fuels, humans pump carbon dioxide into the atmosphere. Fortunately, plants and ocean waters gather it in. But what happens when the planet's great carbon recycling system goes awry?



Get a taste of what awaits you in print from this compelling excerpt.

It's there on a monitor: the forest is breathing. Late summer sunlight filters through a canopy of green as Steven Wofsy unlocks a shed in a Massachusetts woodland and enters a room stuffed with equipment and tangled with wires and hoses.

The machinery monitors the vital functions of a small section of Harvard Forest in the center of the state. Bright red numbers dance on a gauge, flickering up and down several times a second. The reading reveals the carbon dioxide concentration just above the treetops near the shed, where instruments on a hundred-foot (30-meter) tower of steel lattice sniff the air. The numbers are running surprisingly low for the beginning of the 21st century: around 360 parts per million, ten less than the global average. That's the trees' doing. Basking in the sunshine, they inhale carbon dioxide and turn it into leaves and wood.

In nourishing itself, this patch of pine, oak, and maple is also undoing a tiny bit of a great global change driven by humanity. Start the car, turn on a light, adjust the thermostat, or do just about anything, and you add carbon dioxide to the atmosphere. If you're an average resident of the United States, your contribution adds up to more than five metric tons of carbon a year.

The coal, oil, and natural gas that drive the industrial world's economy all contain carbon inhaled by plants hundreds of millions of years ago—carbon that now is returning to the atmosphere through smokestacks and exhaust pipes, joining emissions from forest burned to clear land in poorer countries. Carbon dioxide is foremost in an array of gases from human activity that increase the atmosphere's ability to trap heat. (Methane from cattle, rice fields, and landfills, and the chlorofluorocarbons in some refrigerators and air conditioners are others.) Few scientists doubt that this greenhouse warming of the atmosphere is already taking hold. Melting glaciers, earlier springs, and a steady rise in global average temperature are just some of its harbingers.

By rights it should be worse. Each year humanity dumps roughly 8 billion metric tons of carbon into the atmosphere, 6.5 billion tons from fossil fuels and 1.5 billion from deforestation. But less than half that total, 3.2 billion tons, remains in the atmosphere to warm the planet. Where is the missing carbon? "It's a really major mystery, if you think about it," says Wofsy, an atmospheric scientist at Harvard University. His research site in the Harvard Forest is apparently not the only place where nature is breathing deep and helping save us from ourselves. Forests, grasslands, and the waters of the oceans must be acting as carbon sinks. They steal back roughly half of the carbon dioxide we emit, slowing its buildup in the atmosphere and delaying the effects on climate.

Who can complain? No one, for now. But the problem is that scientists can't be sure that this blessing will last, or whether, as the globe continues to warm, it might even change to a curse if forests and other ecosystems change from carbon sinks to sources, releasing more carbon into the atmosphere than they absorb. The doubts have sent researchers into forests and rangelands, out to the tundra and to sea, to track down and understand the missing carbon.

Click here to read the entire story, which won the 2005 Walter Sullivan Award for Excellence in Science Journalism. 


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Rescued from the cutting room floor is this month's Final Edit, a dreamlike image of an egret wading near shell-laden rocks on Florida's Sanibel Island.

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More to Explore

In More to Explore the National Geographic magazine team shares some of its best sources and other information. Special thanks to the Research Division.

Did You Know?
Concrete is not only the world's most widely used building material, it's also the most abundant human-made solid material. Approximately two tons of concrete for each person on Earth is produced every year. One of the main components of concrete is the cement that binds the small pieces of rock, known as aggregates, together. One of the by-products of cement manufacture is the greenhouse gas carbon dioxide, and because cement production is increasing every year, so too are carbon dioxide emissions.  The annual global production of cement is about 1.8 billion metric tons (China leads the way with more than 700 million metric tons), putting close to 1.5 billion metric tons of carbon dioxide into the atmosphere. Companies are now researching and developing eco-friendly cements, such as blended and geopolymeric cements, that produce fewer carbon dioxide emissions by using less carbon-based raw materials and technologies that require less fuel and heating in their production.
 
To see a yearly list of global carbon dioxide emissions from cement manufacture and fossil-fuel burning since 1751, visit
cdiac.esd.ornl.gov/ftp/ndp030/global00.ems.
 
For more information on cement production, visit
minerals.usgs.gov/minerals/pubs/commodity/cement.
 
—Heidi Schultz
Did You Know?

Related Links
The Carbon Dioxide Information and Resource Center
cdiac.esd.ornl.gov
Track current and historical data on atmospheric carbon dioxide levels as well as other greenhouse gases.
 
Woods Hole Research Center
www.whrc.org
Check out presentations on the carbon cycle and warming of the Earth to learn more about global climate change.
 
United Nations Environment Programme Climate Change Graphics
www.grida.no/climate
Learn about climate change with diagrams of the carbon cycle, greenhouse effect, human-related carbon dioxide emissions, and rising sea levels.
 
The Biology of Plants
www.whfreeman.com/raven/index.htm
Study the ins and outs of photosynthesis and respiration with this interactive online textbook complete with flashcards, videos, exercises, and additional Web links.
 
United Nations Framework Convention on Climate Change
unfccc.int/press/dossiers/index.html
Access a wealth of material on climate change basics from the official website for the international Convention on Climate Change and the Kyoto Protocol.

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Bibliography
Intergovernmental Panel on Climate Change. Climate Change 2001: The Scientific Basis. Cambridge University Press, 2001. Available online at www.grida.no/climate/ipcc_tar/wg1/index.htm.

Priestley, Joseph. Experiments and Observations on Different Kinds of Air, and Other Branches of Natural Philosophy, Connected With the Subject. 1790. Reprint, Kraus Reprint Co., 1970.

Sarmiento, Jorge, and Nicolas Gruber. "Sinks for Anthropogenic Carbon," Physics Today (August 2000), 30-6. Available online at
www.aip.org/pt/vol-55/iss-8/p30.html.
 
Smil, Vaclav. Cycles of Life: Civilization and the Biosphere. Scientific American Library, 2001.

State of the Nation's Ecosystems. The Heinz Center, 2002. Available online at
www.heinzctr.org/ecosystems/report.html.

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NGS Resources
Cahill, Tim. "Into Bad Air! The CO2 Chronicles," National Geographic Adventure (November 2003), 54-60, 62,101-6.
 
Johnson, Rebecca L. Global Warming. National Geographic Books, 2002.

Suplee, Curt. "Unlocking the Climate Puzzle," National Geographic (May 1998), 38-71.
 
Matthews, Samuel W. "Under the Sun—Is Our World Warming?" National Geographic (October 1990), 66-99.

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