[EMAIL PROTECTED] wrote:
> I am not sure what is meant by "commit" and "might still be avoided"
> here. It makes me think of "tipping points" and irreversibilities.
> Maybe by 2100 after having blown past 600 ppm, even reducing CO2 back
> to 300 ppm by 2200 would still mean 5 m by 2500, assuming nothing else
> is done between 2200 and 2500 (say local albedo enhancement or
> whatever). I accept it's possible that going to 300 ppm by 2200
> mightn't be enough to reverse the "commitment",
I don't believe there is any scientific basis for these sort of
opinions. All of the "commitment" stuff is based on maintaining constant
GHG levels into the future, and _not_ especially on the principle that
we might actually flip over a hysteresis threshold. On glacial time
scales, as soon as we reduce the CO2 enough, the temperature comes down
and the melting stops. There is quite possibly a hysteresis if Greenland
does melt, but that "flip" is expected to take at least several hundred
years.
Actually I'm not aware of anyone having done precisely this modelling
experiment (rapid reduction of CO2) but that is probably because it is
(a) bloody obvious and (b) politically unattractive. Anyone who takes
Branson's air capture prize seriously might plausibly consider that this
CO2 reduction can be left to 6 generations hence, if they choose to go
back to a colder world. OTOH, studies that show that the temp at 2100
will probably be at a level which will melt Greenland in the long term
(if the temperature stays high for long enough) make Nature papers and
headlines :-)
James
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