sci.energy

>Reply to article by: Jonathan Kirwan
>Date written: Mon, 06 Aug 2007 21:59:25 GMT
>MsgID:<7r4fb3p3151jj7rvqjjhi9fbh02mfprhr1@ >

>>> >Abstract. Recent analyses indicate that the amount of atmospheric CO2
>>> >required to cause dangerous climate change is at most 450 ppm, and
>>> >likely less than that.

>>> Past analysis has shown that 4400 ppm during the Late Ordovician period had
>>> little effect on temperature. How does "recent analysis" account for that?

>>OK how was the 4400 ppm determined?

>I'd like to know that, as well. I did see such a figure in a Letter
>in Nature called "Climate sensitivity constrained by CO2
>concentrations over the past 420 million years" by Dana L. Royer,
>Robert A. Berner, and Jeffrey Park. If you look at their graph and
>chose the line that assumes a sensitivity of C/2xCO2, and go back
>to the earliest part of the chart you can see a projection that says
>about that figure. However, sensitivities are much more likely about
>twice that and the resulting modified GEOCARBSULF model would say
>something closer to 2400 ppmv.

>Of course, this is a VERY LONG TIME AGO.. some 450 million years back,
>if memory serves. I know that there are papers doing studies of
>certain carbonaceous fossils that may go back to the Eocene, or so, as
>possible proxies for CO2 levels and/or ocean temperatures. I can't
>recall reading any papers on what proxies exist for that long ago,
>though, and I don't recall what the paper I just mentioned said about
>them, if anything.

The CO2 levels were determined by O18 to O16 ratios in marine carbonate. See
/GG/FACULTY/POPP/Royer%20et%20al.%202004%20GSA%

The Sage

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"It is a cold fact: the Global Cooling presents humankind
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