Transcript Radiation and Climate_The Carbon Cycle

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 atmosphere
b) 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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