The August PHYSICS TODAY magazine features a disturbing article on carbon
dioxide trapping ("Sinks for Anthropogenic Carbon") & its relation to
global warming.
Here's the gist of the article. Quotes are the authors, and caps are mine.
The authors are Jorge Sarmiento (Princeton) and Nicolas Gruber (UCLA).
DEFINITION:
Anthropogenic: "of, pertaining to, or resulting from the influence of human
beings on nature" (Webster's Dictionary)
FACTS:
* Because of anthropogenic emissions, atmospheric carbon dioxide has
climbed to 30% higher than before the industrial revolution.
* More than half of the increase in trapping of long wavelength radiation
emitted from the Earth's surface is attributed to carbon dioxide (the rest
is due to methane, nitrous oxide, chlorofluorocarbons, etc.)
* The increased trapping will lead to global warming.
CONCLUSION:
"Humankind thus appears to be playing a significant role in altering
Earth's climate."
THE CARBON CYCLE:
The growth rate of atmospheric carbon dioxide "is less than half of what
would be expected if all the carbon dioxide released by fossil-fuel burning
and land-use change remained in the atmosphere". This is because land
(plants & soil) and oceans are taking it up, i.e., acting as "sinks" -
which is good! The land sink "appears to be as large a carbon sink as the
oceans" (but uncertainties in both are large, of course).
THE PUZZLING THING:
Until a few years ago, scientists thought that the dominant land sink
mechanism were fertilizing effects [of increased carbon dioxide in the
atmosphere and the addition to soils of fixed nitrogen from fossil-fuel
burning, etc.] But this is not true, scientists recently found in various
long-term studies! The fertilization sink mechanism is small.
Their next step was to find the true sink mechanisms. To do this,
scientists recently analyzed the land sinks in the U.S.A., where the data
are best and the model analysis is best.
WHAT'S SCARY: They find that "the largest sink is due to regrowth in
abandoned farmland and areas that had previously been logged." The second
most important sink mechanism is "the encroachment of woody growth into
areas where fires have been suppressed, especially in the southwest".
Why is that scary? Because "the global carbon dioxide uptake CAPACITY from
changes in land-use such as forest regrowth is much more MODEST than that
[previously] predicted for fertilization". [Another reason it might be
scary, although the authors don't mention it, is the brand-new legislation
to increase logging and burning, including in the southwest.]
THE BIG PICTURE:
The authors combine these findings with other data to model long-term
atmospheric changes. They conclude: "it's safe to say there are no magic
bullets in the carbon sinks to rescue the world from high atmospheric
carbon dioxide levels any time in the next few centuries. Quite to the
contrary, most of the feedbacks between the global carbon cycle and global
warming seem to be positive -- that is, GLOBAL WARMING REDUCES THE SINK
STRENGTHS." That's another scary thing.
THE BOTTOM LINE:
"Currently, the only method that can be guaranteed to mitigate the expected
increases in atmospheric carbon dioxide is REDUCED FOSSIL-ENERGY
UTILIZATION."
cheers (?),
Jane Jackson
Jane Jackson, Co-Director, Modeling Instruction Program
Box 871504, Dept.of Physics & Astronomy,ASU,Tempe,AZ 85287
480-965-8438/fax:965-7331 <http://modeling.asu.edu>
"The greatest shortcoming of the human race is
our inability to understand the exponential function."
- Al Bartlett, Prof of Physics, Univ of Colorado