OT: Bush's Secret Campaign To Deny Global Warming
- From: Bruce Newin Town-Saylor <nobody@xxxxxxxxxxxxxxxxx>
- Date: Thu, 5 Jul 2007 16:31:36 -0600 (MDT)
'Bruce' knows that a corporate polluter website is the best place to
shop for his 'facts':
Your numbers are meaningless. Humans contribute about 3.225% of CO2******************************************************************
that is emitted to the atmosphere. Total CO2 emissions to the
atmosphere is only 3.618% of all greenhouse gasses.
Here's the truth:
Over the last 150 years, carbon dioxide (CO2) concentrations have risen
from 280 to nearly 380 parts per million (ppm). The fact that this is
due virtually entirely to human activities is so well established that
one rarely sees it questioned. Yet it is quite reasonable to ask how we
know this.
One way that we know that human activities are responsible for the
increased CO2 is simply by looking at historical records of human
activities. Since the industrial revolution, we have been burning fossil
fuels and clearing and burning forested land at an unprecedented rate,
and these processes convert organic carbon into CO2. Careful accounting
of the amount of fossil fuel that has been extracted and combusted, and
how much land clearing has occurred, shows that we have produced far
more CO2 than now remains in the atmosphere. The roughly 500 billion
metric tons of carbon we have produced is enough to have raised the
atmospheric concentration of CO2 to nearly 500 ppm. The concentrations
have not reached that level because the ocean and the terrestrial
biosphere have the capacity to absorb some of the CO2 we produce.*
However, it is the fact that we produce CO2 faster than the ocean and
biosphere can absorb it that explains the observed increase.
Another, quite independent way that we know that fossil fuel burning and
land clearing specifically are responsible for the increase in CO2 in
the last 150 years is through the measurement of carbon isotopes.
Isotopes are simply different atoms with the same chemical behavior
(isotope means ?same type?) but with different masses. Carbon is
composed of three different isotopes, 14C, 13C and 12C. 12C is the most
common. 13C is about 1% of the total. 14C accounts for only about 1 in 1
trillion carbon atoms.
CO2 produced from burning fossil fuels or burning forests has quite a
different isotopic composition from CO2 in the atmosphere. This is
because plants have a preference for the lighter isotopes (12C vs. 13C);
thus they have lower 13C/12C ratios. Since fossil fuels are ultimately
derived from ancient plants, plants and fossil fuels all have roughly
the same 13C/12C ratio ? about 2% lower than that of the atmosphere. As
CO2 from these materials is released into, and mixes with, the
atmosphere, the average 13C/12C ratio of the atmosphere decreases.
Isotope geochemists have developed time series of variations in the 14C
and 13C concentrations of atmospheric CO2. One of the methods used is to
measure the 13C/12C in tree rings, and use this to infer those same
ratios in atmospheric CO2. This works because during photosynthesis,
trees take up carbon from the atmosphere and lay this carbon down as
plant organic material in the form of rings, providing a snapshot of the
atmospheric composition of that time. If the ratio of 13C/12C in
atmospheric CO2 goes up or down, so does the 13C/12C of the tree rings.
This isn?t to say that the tree rings have the same isotopic composition
as the atmosphere ? as noted above, plants have a preference for the
lighter isotopes, but as long as that preference doesn?t change much,
the tree-ring changes wiil track the atmospheric changes.
Sequences of annual tree rings going back thousands of years have now
been analyzed for their 13C/12C ratios. Because the age of each ring is
precisely known** we can make a graph of the atmospheric 13C/12C ratio
vs. time. What is found is at no time in the last 10,000 years are the
13C/12C ratios in the atmosphere as low as they are today. Furthermore,
the 13C/12C ratios begin to decline dramatically just as the CO2 starts
to increase -- around 1850 AD. This is exactly what we expect if the
increased CO2 is in fact due to fossil fuel burning. Furthermore, we can
trace the absorption of CO2 into the ocean by measuring the 13C/12C
ratio of surface ocean waters. While the data are not as complete as the
tree ring data (we have only been making these measurements for a few
decades) we observe what is expected: the surface ocean 13C/12C is
decreasing. Measurements of 13C/12C on corals and sponges -- whose
carbonate shells reflect the ocean chemistry just as tree rings record
the atmospheric chemistry -- show that this decline began about the same
time as in the atmosphere; that is, when human CO2 production began to
accelerate in earnest.***
In addition to the data from tree rings, there are also of measurements
of the 13C/12C ratio in the CO2 trapped in ice cores. The tree ring and
ice core data both show that the total change in the 13C/12C ratio of
the atmosphere since 1850 is about 0.15%. This sounds very small but is
actually very large relative to natural variability. The results show
that the full glacial-to-interglacial change in 13C/12C of the
atmosphere -- which took many thousand years -- was about 0.03%, or
about 5 times less than that observed in the last 150 years.
For those who are interested in the details, some relevant references
are:
Stuiver, M., Burk, R. L. and Quay, P. D. 1984. 13C/12C ratios and the
transfer of biospheric carbon to the atmosphere. J. Geophys. Res. 89,
1731?1748.
Francey, R.J., Allison, C.E., Etheridge, D.M., Trudinger, C.M., Enting,
I.G., Leuenberger, M., Langenfelds, R.L., Michel, E., Steele, L.P.,
1999. A 1000-year high precision record of d13Cin atmospheric CO2.
Tellus 51B, 170?193.
Quay, P.D., B. Tilbrook, C.S. Wong. Oceanic uptake of fossil fuel CO2:
carbon-13 evidence. Science 256 (1992), 74-79
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http://www.realclimate.org/index.php?p=87
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