[Vision2020] Hansen et. al.: Atmospheric CO2: Where Should Humanity Aim?

[Ted Moffett]

At URL at bottom is a draft of a as yet unpublished (as far as I know)
scientific paper by Hansen et. at. arguing that the current atmospheric CO2
level of 385 ppm, much less the higher CO2 level (450 ppm) targets that are
proposed as reasonable goals in greenhouse gas mitigation, is too high to
avoid serious long climate change.

As I posted to Vision2020 previously,
http://mailman.fsr.com/pipermail/vision2020/2008-July/055108.html
climate sensitivity (temperature change for doubling atmospheric CO2) is ~3
C., a figure arrived at via averaging the scientific work examining climate
sensitivity going back to Arrhenius in 1896 (sourced from Barton Paul
Levenson's research),
http://members.aol.com/bpl1960/ClimateSensitivity.html

I was surprised to find this ~3 C. climate sensitivity estimate (not sourced
from Barton Paul Levenson, as far as I know) in this paper, a figure Hansen
et. al. suggest below is the climate sensitivity only including "fast
feedback processes."  Including "slow feedback processes...," climate
sensitivity is ~6 C., as this paper proposes.  I trust I do not need to
emphasize with alarming descriptions what a 6 degree C. (or even ~3 degree
C.), 10.8 degree Fahrenheit change in global average temperature would mean:

Quote from the paper under discussion:

"If humanity wishes to preserve a planet similar to that on which
civilization developed and to which life on Earth is adapted,
paleoclimate evidence and ongoing climate change suggest that CO2 will need
to be reduced from its current 385 ppm to at most 350 ppm."

http://www.columbia.edu/~jeh1/2008/TargetCO2_20080407.pdf

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Vision2020 Post: Ted Moffett
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