Over the relevant range of variation in CO2, you make only a modest
error (a little less than 10%) by assuming forcing is linearly
proportional to CO2 rather than logarithmically.

Given that a large portion of the temperature change is driven by
albedo changes and other indirect forcing, rather than directly by
CO2, I think it is very difficult to empirically discriminate between
linear and logarithmic response during the ice age transition.  Of
course, laboratory work shows a clearly logarithmic response, but the
Earth is a noisy environment and the limited range of variation during
the ice ages doesn't provide a strong basis for identifying the
logarithmic characteristics.

However, the range of variation between the ice ages and where we are
going now should provide a much more practical "experiment" for seeing
the logarithmic characteristics.

-Robert A. Rohde
http://www.globalwarmingart.com/

On Oct 4, 5:35 am, Tom Adams <[EMAIL PROTECTED]> wrote:
> Both the temp and CO2 increase looks linear during the rapid rise when
> the Earth is going from a glacial to inter-glacial:
>
> http://www.globalwarmingart.com/wiki/Image:Carbon_Dioxide_400kyr_Rev_png
>
> http://www.globalwarmingart.com/wiki/Image:Ice_Age_Temperature_Rev_png
>
> The log relationship between CO2 conc. and temp. is not reflected in
> this period of rapid rise.  Why not?


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