[EMAIL PROTECTED] wrote:
>> 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.
>
> If emissions go down enough, then even without sequestration
> concentrations will fall, and I think over a 1000 year time frame
> starting at 450 ppm they'd fall to around 300 ppm (?).
>
>>From this it would follow that as long as there isn't a hysteresis as
> you call it in between, stopping emissions would be enough to
> eventually reverse most of the melting.
Your numbers seem a little optimistic to me, but roughly speaking that's
right. However if we got to 550ppm and then stopped all emissions then I
would guess that the melting could beat the natural CO2 decline. Note
that the melt wouldn't need to be complete before the CO dropped below
whatever the current melting threshold is, as the reduction in elevation
and increased overall albedo would make the ice sheet more vulnerable
(effectively, it would be a race between the ongoing melt and the
overall global temperature drop).
It might be a fun thing to do with our new coupled climate / ice-sheet /
carbon cycle model, except it's not quite built yet...
> What is your opinion on what is possible in terms of taking CO2 out of
> the air?
Clearly none of the direct extraction methods seem close to viable in
current economic terms, but I wouldn't like to say it will still be
impossible in 100 years or more! OTOH I have my doubts as to whether
people would actually choose to go back to a significantly colder planet
100 years from now, once they are used to most of the changes. After
all, that would just be piling another change on top of the (then)
recent past one which they would have just got used to. OK, that ignores
the threat of long-term sea level rise which some nations might
reasonably be upset about - but would they be rich and powerful enough
to do anything about it?
> I am not sure what Branson's prize is about exactly. Presumably it
> would be for technology that could do the CO2 removal at very low
> energy and overall cost? What I've read about it sounds awfully vague.
Agreed. I have looked for more info in vain. It seems to have been a
sort of pre-launch.
James
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