Radiation and Climate

The Carbon Cycle

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The Carbon Cycle

• More than a century ago, it was suggested that a significant increase in burning fossil fuels might release enough carbon dioxide into the atmosphere to affect Earth’s surface temperature.– This was based on the idea that human activity can

affect processes in natural ecosystems, producing changes that might not always be beneficial.

– Burning fossil fuels might perturb the natural movement of carbon within Earth’s systems – the global carbon cycle.

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Chemical Reservoirs

• In the carbon cycle, the different forms and compounds in which carbon atoms are found can be considered as “chemical reservoirs” of carbon atoms.

• These reservoirs include atmospheric CO2 gas, solid calcium carbonate (CaCO3) in limestone, natural gas (methane, CH4), and organic molecules.

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The carbon cycle – major pathways within the biosphere.

Respiration:C6H12O6 + 6 O2 6 CO2 + 6 H2O

Photosynthesis:6 CO2 + 6 H2O C6H12O6 + 6 O2

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The carbon cycle—relationships among major carbon reservoirs

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Energy within the Carbon Cycle

• Each movement within the carbon cycle, and thus among these reservoirs, either requires energy or releases energy.– Plants use CO2 and solar energy to form

carbohydrates through photosynthesis.– The carbohydrates are consumed by other

organisms (or by the plant itself) and are eventually broken down or oxidized, releasing energy for use by organisms that consumed them.

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Global Carbon• The carbon atoms used in and circulated in

photosynthesis represent only a tiny portion of available global carbon.– Gaseous CO2 continually moves between the

atmosphere and the oceans.• 71% of Earth’s carbon atoms, in the form of CO2 are

dissolved in the oceans.• Another 22% are trapped in fossil fuels and in carbonate

rocks formed when dissolved CO2 reacted with water, which first produced carbonates, then sediments, then rocks.

• Dead organisms and terrestrial ecosystems (such as trees, crops, and other living matter) account for the remaining global carbon-atom inventory

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Anthropogenic Carbon Dioxide • Without the influence of human activities, the

distribution of carbon within various reservoirs would remain relatively unchanged over time.

• Atmospheric CO2 levels, however, have increased by about 30% since 1800.

• This increase is the result of several processes:– Clearing forests removes vegetation that would normally

consume CO2 through photosynthesis– As cuttings and scarp timber are burned, they release CO2

into the atmosphere– Burning fossil fuel releases CO2 into the air (most

significant)

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CO2 Sources

• Burning coal: C (s) + O2 (g) CO2 (g)

• Burning natural gas: CH4 (g) + 2 O2 (g) CO2 (g) + 2 H2O (g)

• Burning gasoline: 2 C8H18 (g) + 25 O2 (g) 16 CO2 (g) + 18 H2O (g)

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How does each of these scenes affect atmospheric carbon dioxide levels?

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HOMEWORK

1) Describe how atmospheric CO2 and water vapor help maintain moderate temperatures at Earth’s surface.

2) List two natural processes and two human activities that can increase the amount of

a) CO2 in the atmosphereb) CH4 in the atmosphere

3) List three chemical reservoirs of carbon atoms.

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HOMEWORK

4) Explain how, over time, a particular carbon atom can be part of the atmosphere, biosphere, lithosphere, and hydrosphere.

5) Write a chemical equation that depicts the transfer of a carbon atom between any two of “spheres” listed in Question 4.

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