Re: Global warming problems in homeschool text

From: Glenn Morton <>
Date: Fri Aug 19 2005 - 19:53:27 EDT

Joel Moore <> wrote:
The theory behind global warming is actually pretty simple and goes
back to Arrhenius in the 1890s. CO2 traps more heat than most gases
and without the presence of CO2 in the atmosphere the earth would be a
lot cooler than the present. In essence, since that time people have
been trying to figure out how much things will change and warm up (or
perhaps cool in some regions, like northern Europe) as humans add CO2
to the atmosphere.

A couple of quick points Glenn.

Geologic time.... I'm pretty sure the Cerling paper on the Miocene is
out of date and new evidence shows lower CO2 in the Miocene than was
previously thought. Pagani et al. 1999 or 2000 is one of the relevant

GRM: But I didn't mention the Miocene. I mentioned the Cretaceous. You are correct that Cerling discusses the miocene but he gives an UPPER limit, not a lower limit. He said it was less than 700 ppm but didn't say how much less. My point is not the nits and picks about whether it is 700 or 500 in the Miocene. My point was what I mentioned, the Cretaceous, and I don't believe that he is out of date on the Cretaceous. This is from a 2002 article. Retallack, CArbon Dioxide and Climate over the past 300 million years," Philosophical Transactions, Mathematical, Physical and Engineering Sciences, 360: 659-673


"Past CO2 highs (above 2000 ppmv) were not only times of catastrophic release of CH4 from clathrates, but of asteroid and comet impacts, flood basalt eruptions and mass extinctions. The primary reason for iterative return to low CO2 was carbon consumption by hydrolytic weathering and photosynthesis, perhaps stimulated by mountain uplift and changing patterns of oceanic thermohaline circulation. Sequestration of carbon was promoted in the long term by such evolutionary innovations as the lignin of forests and the sod of grasslands, which accelerated physicochemical weathering and delivery of nutrients to fuel oceanic productivity and carbon burial."

My point was, and still remains that in the past the earth has had periods of very high CO2 content. Does it heat the earth? Yes. Does it wipe out life? some, but not all.

Joel continues:

Also, overall atmospheric CO2 levels have been declining for
millions to hundreds of millions of years but the strength of the sun
has been increasing. CO2 (and methane and other greenhouse gases)
concentrations billions of years ago needed to be much higher because
the strength of the sun was significantly less than the present.

GRM: I would submit that the change in solar irradiance over the last 65 million years has been miniscule compared with the percentage of CO2 change in the same interval.

Joel continues:

More modern... No strong evidence exists for the global average
temperature being higher in 800 AD than the present. The temperature
in the northern hemisphere may have been close to as warm for a few
years, but it is not likely that any 3-decade period in the last 1000
or more years has been as warm as the last 3 decades. Also, higher
temperatures in one area or region do not mean that the global average
temperature was higher (or even the average temperature of the
northern hemisphere was higher).

I do stand corrected here. Thank you. The Medieval warm epoch does not seem to have been warmer than today according to the articles I just read.



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Received on Fri Aug 19 19:54:31 2005

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