OUTPUTS OF CO2 FROM THE ATMOSPHERE
- Outputs of carbon dioxide from the atmosphere are either
biological, geological, or anthropogenic.
Biological outputs are mediated by photosynthesis.
Geological outputs occur as the net result of oceanic-atmospheric interactions.
- Anthropogenic outputs occur when humans act to purposely
reduce the inputs of carbon dioxide to the atmosphere,
e.g., through fossil-fuel energy conservation.
- The main output of carbon dioxide is through biological sequestering.
Photosynthesis takes carbon dioxide from the air
and incorporates it into the biosphere as organic matter.
If the carbon returns to the atmosphere in the short term
(mostly through respiration), it is recycled;
conversely, if the carbon is not returned to the atmosphere
in the short term, it is sequestered.
- Photosynthesis takes place in terrestrial and aquatic ecosystems, including the oceans.
For any ecosystem, rates of biological sequestering
are equal to the difference between rates of productivity and rates of respiration.
In tropical rain forests, where rates of respiration closely match rates of productivity,
there is little sequestering of carbon (Welch, 1992).
On the other hand, the photosynthesis of algae and other plants floating
in the surface layers of the ocean is more likely to result in sequestering.
The respiration of animals in the oceans being less
than the productivity, biological sequestering takes place through
the settling of dead organic matter to the bottom of the ocean
(IPCC, 1996a).
- Mass balances show that only about half of the carbon dioxide
emitted to the atmosphere in industrial times remains in the atmosphere.
The unaccounted portion must be going either to increase the biomass
of terrestrial and oceanic ecosystems, or to additional sequestering
through oceanic-atmospheric interactions.
- Evidence for the increase of biomass is scant
and difficult to document, although the Amazon rain forest,
the largest terrestrial ecosystem in the world,
appears to be expanding along its perimeter (Prance, 1985).
Little is known about a possible biomass growth
in the surface layers of the oceans; however,
there is reason to suspect that it is there.
If indeed the biosphere is growing in the oceans,
its effectiveness as a carbon sink would be analogous to that
of the cultural eutrophication of lakes and estuaries.
Recent efforts to artificially increase oceanic biomass through
iron fertilization have been made, although with mixed results to date
(IPCC, 1996a).
- Oceanic/atmospheric interactions are presumed to be responsible
for the additional sequestering of carbon (IPCC, 1996a).
The ocean is estimated to have taken up about thirty percent
of anthropogenic carbon dioxide emissions between 1980 and 1989,
thereby slowing the rate of climate change (IPCC, 1996b).
- Anthropogenic reductions in input of carbon dioxide to the atmosphere
amount to outputs from the reservoir. Examples are:
- Energy conservation measures which result in
net reductions in fossil-fuel combustion.
-
The conservation and restoration of natural ecosystems,
which by amounting to permanent increases in the carbon sink,
are the exact opposite of permanent indirect artificial combustion.
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