Re: Scientist: Warming not caused by humans

Jake wrote:

Matthew Scott wrote:

I feel that if the anthropomorphic warming proponents can assign a
specific cause to the current warming cycle and predict the future,
they ought to be able to interpret the past and explain previous
cycles of warming and cooling when man was not burning fossil fuels.


The term warming and cooling cycles trivializes the danger since the
actual
maximum cycling in geological time is between hot and cold extremes.
So it is
better to use at least three terms, cold, moderate and hot. In polar
ice caps exist with the first two, not with the latter. We are still
in the moderate range right now. The earth is currently in a period of cold-moderate cycling,
exceptional
when viewed over the last 450 million years, where the atmospheric
CO2 is now low (well below 1000 ppm), and has
been over the last 650,000 years cycling period, varying between
200-300 ppm. The temperature variations have been severe
(8°C) and the climate differences radical even during the short
period modern man has been around. Nobody would like to
see the return of the Northern Hemisphere ice sheets and if the
temperature were headed down we might even chose a policy of
releasing more CO2 in the atmosphere and/or black dusting the
ice sheets so that the albedo would change and the sun's heat
absorbed.
We are at the opposite end of that problem and it behooves us to
estimate
much much heating will occur at various higher CO2 levels. We do have
geological
records to look at. But we know that other factors are at work in
influencing
both local and global climate. The earth precesses, and winter
becomes
summer every 5000 or so years. The earth is on slightly eliptical path
around the sun, the solar constant effectively varies by couple of
%, the short term sunspot cycle does not change the constant much
(0.1%) but other changes occur which may influence cloud formation.
But most of use think the CO2 change is in the driver's seat right
now.
The last big warm period was during the Miocene during which the CO2
content was greater than 1125 ppm (four times preindustrial
concentrations),
There were no ice caps, there was a period of rapid change generating
the
Paleocene-Eocene Thermal Maximum (PETM). "The period was marked by a
rapid rise in greenhouse gases that heated Earth by roughly 9° F (5°
C), in less than 10,000 years. The climate warming caused widespread
changes including mass extinction in the world's oceans due to
acidification and shifts of plant communities due to changes in
rainfall."
The opposite problem occurred at the end of the Carboniferous,
apparently
photosynthesis had sent the CO2 levels to very low values, the climate
radically changed from hot to cold.
"Average global temperatures in the Early Carboniferous Period were
hot- approximately 20° C (68° F). However, cooling during the Middle
Carboniferous reduced average global temperatures to about 12° C (54°
F). As shown on the chart below, this is comparable to the average
global temperature on Earth today!"
"Similarly, atmospheric concentrations of carbon dioxide (CO2) in the
Early Carboniferous Period were approximately 1500 ppm (parts per
million), but by the Middle Carboniferous had declined to about 350
ppm -- comparable to average CO2 concentrations today!" "Earth's atmosphere today contains about 380 ppm CO2 (0.038%).
Compared to former geologic times, our present atmosphere, like the
Late Carboniferous atmosphere, is CO2- impoverished! In the last 600
million years of Earth's history only the Carboniferous Period and our
present age, the Quaternary Period, have witnessed CO2 levels less
than 400 ppm."
That pretty much tells the CO2 story. If we eventually push the CO2
level
too high, like over 1000, we risk a lot, including mass extinctions
and we may be one of the victims of that.



That's all very interesting, but you still haven't connected the dots.

If mankind wasn't burning fossil fuels to cause an increase of carbon dioxide in the earlier cycles that you describe, why will reducing mankind's carbon dioxide releases (but only in SOME countries) today have any appreciable effect on the warming cycle the earth is now in? What is so different between those earlier epochs and today, and how is the difference, if it exists, affecting the temperature cycle? How does the presence or absence of mankind affect the temperature cycles? What exactly caused "The last big warm period . . . during the Miocene during which the CO2 content was greater than 1125 ppm (four times preindustrial concentrations)".
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