Energy and Changes in the Environment - Hydrogen and Fuel Cells: Advances in Transportation and Power - page 52

almost as much weight in carbon atoms as all the animals together and
fungi have about half that amount. Dead organic matter, mostly in soils,
contains about twice as much carbon as does the atmosphere.
BIOLOGICAL MODERATION
Biological feedback processes can be expected to affect the amounts of
carbon dioxide that might be injected into the air over the next century.
As CO 2 increases, green plants could take up more carbon dioxide
into plant tissues through photosynthesis reducing slightly the buildup of
CO 2 . This could moderate some of the greenhouse effect.
However raising the temperature in the soils by a few degrees may
increase the activity rates of bacteria that convert dead organic matter into
CO 2 .
This is a positive feedback loop since warming would increase the CO 2
produced in the soils, further increasing the warming. The EPA thinks there
is a real potential for major positive feedback that could greatly increase
greenhouse effects. There are more than a dozen biological feedback
processes that could affect estimates of the temperature sensitivity to
greenhouse gases due to human activities. If all of these operate in unison,
it could double the sensitivity of the climatic system to the initial effects of
greenhouse gases. This would be a possible but worst case situation. The
time frame over which these processes could occur is estimated at several
decades to a century or more.
CLIMATE MODELS
Most climate models show a climate in stable equilibrium. If the
1900 condition of 300 parts per million doubles to 600 ppm, most three-
dimensional models indicate an equilibrium with an average surface
temperature warming of 3.5° to 5°C (5.6° to 9°F). If the carbon dioxide
content of the atmosphere doubled in one month, the earth's temperature
would not reach its new equilibrium value for a century or more.
If we were able to limit all CO 2 emissions, we could still expect about
one degree of warming while the climatic system catches up with the
greenhouse gases already released. It is not the global average temperature
that is most important but it is the regional patterns of climate change.