2011-01-01 17:44:33Basic Rebuttal #103. Carbon Dioxide levels were higher in the late Ordovician.



Those who deny that there is man made global warming claim that Carbon Dioxide has little or no effect on how much warmth the Earth retains. One of the arguments that 'skeptics' use to that effect is that our atmosphere had high levels of Carbon Dioxide in the ancient past, hundreds of millions of years ago, compared to the present. The temperatures back then, however, were not as high as climate scientists predict would happen today if we had the same amounts.

What "skeptics' consistently fail to mention is that the Sun was colder back then than it is today. This means that higher levels of Carbon Dioxide would actually be necessary to maintain an equivalent temperature to our modern Earth whether frigid or hot.

One of the arguments makes reference to the Ordovician, a period of time from 490 to 443 million years ago when Carbon Dioxide levels were up to 14-16 times higher than todaya. During its early phases surface air temperatures were estimated to have been 40o Celsiusb (104o Fahrenheit). During the summer, at the equator, the oceans reached up to 45Cc (113F). As time progressed the continents moved towards the South Pole where modern day Antarctica is located. There was a cooling off as glaciers built up in the southern regions.

Throughout the Ordovician the Sun was about 4.5% colder than it was todayd.


In conclusion, 'skeptics' use the much higher amounts of Carbon Dioxide in the ancient past to claim that it has little effect on our atmosphere's ability to retain heat. But they ignore the fact that our colder Sun would have required that the Earth have more greenhouse gases simply to keep it's oceans from freezing solid all the way down to the equator.


a   http://www.britannica.com/EBchecked/topic/431581/Ordovician-Period

b  Crowley, T.J.; North, G.R. 1991: Paleoclimatology. Oxford University Press.

c  Did cooling oceans trigger Ordovician biodiversification: evidence from conodont thermometry, Julie A. Trotter, Ian S. Williams, Christopher R. Barnes, Christophe Lécuyer & Robert S.Nicoll, Science, July 25, 2008.


e  It may seem counterintuitive that such a drastic drop in temperatures could result from a small reduction in solar ...We have to start out at absolute zero, the coldest temperature possible, and add the Earth's average temperature. Absolute zero is -273.15C (-459.67F). The Earth's average temperature is about 13C (55.4F). The result is a total temperature of about

2011-01-01 19:16:07
Rob Painting


Not surprisingly, oil companies fund the individuals and organizations that come up with arguments like this.

I'd cut that bit out. Undoubtedly true, however will just detract from the rebuttal as "skeptics" seize on it. I think Steve O'Connor essentially covered this one in his "CO2 was higher in the past" basic rebuttal anyway. 

2011-01-02 01:03:30Excision and redundancy.



Had a feeling I'd have to cut that one out.

I did not notice the redundancy. Maybe it could be turned into a post without having to be a rebuttal.

2011-01-04 19:08:23Deliberate intention, global temperature, and some other things
James Wight


I think the opening places slightly too much emphasis on the “skeptics”, whereas the emphasis should be on the argument itself. Similarly, in the last paragraph I would remove the word “deliberately” as we cannot read the minds of those who make this argument, nor should we tar them all with the same brush.

Are the 40°C and 45°C degrees global numbers? If so, that would be something like 25°C hotter than today, in which case a runaway greenhouse seems more likely than a glaciation.

A few other comments:

  • “Carbon Dioxide” and “Global Warming” should not be capitalized.
  • In my opinion the words “whether frigid or hot” at the end of the second paragraph are unnecessary and confusing.
  • In the fourth paragraph, “colder than it was today” should be “colder than it is today”.
  • Something is missing at the end of the fourth paragraph. In any case, I think the discussion of absolute temperature is an unnecessary digression.
  • Also, there is no text in footnote d.
2011-01-05 05:36:23Incomplete post.



I made some clarifications to the temps and changes in phrasing as you suggested.

As far as Ordovician glaciations are concerned my understanding is that CO2 levels went below 3,000 ppm during that phase. That is still congruent with the 14-16X levels when compared to the 180 ppm of our Quaternary glaciations. I might have to redo the statistics and include absolute CO2 levels for both hot and cold phases of the Ordovician.

The absolute temps, as can be seen by the broken sentence and the dotted separation between the text and the conclusion, was part of an incomplete post. I was in the middle of giving a calculation.

The reason for that digression is because, in the minds of laypersons, a 4.5% reduction in solar irradiance is too small to make more than a few degrees difference considering the huge levels of CO2. I'm afraid skeptics will take advantage of this. I'm going to calculate how much lower a temperature a 4.5% reduction in solar irradiance would give us in a present Earth-explaining the seemingly large discrepancy. I realize that may be too much for a basic level rebuttal, so I might just include the temperature difference in the main text and leave the calculations for a footnote.

In view of all of the above I will probably do a rewrite.