Don Libby wrote:
> ----- Original Message -----
> From: "Tom Adams" <[EMAIL PROTECTED]>
> Newsgroups: gmane.science.general.global-change
> To: "globalchange" <[email protected]>
> Sent: Monday, January 21, 2008 2:25 PM
> Subject: [Global Change: 2386] Re: Is it true?
>
> On Jan 18, 5:55 pm, James Annan <[EMAIL PROTECTED]> wrote:
>> Don Libby wrote:
>>> Today I read a statement in the popular press that strikes me as absurd,
>>> but
>>> is it true?
>>> "The world must reduce carbon emissions by 90% by 2030 to avert an
>>> ecosystem
>>> collapse..."
>> This is probably based on the +2C "dangerous climate change": it is true
>> enough if you equate (the *risk* of) dangerous climate change with "an
>> ecosystem collapse".
>>
>
> Since this contrasts sharply with the opinion I had formed that shallow cuts
> now and deeper cuts later in the Century would be adequate to stabilize at
> or near 2x pre-industrial by 2100 (for example, the IS92c emission
> trajectory), I thought that perhaps some new science had cropped up in the
> last five years that escaped my attention and required me to get busy with
> my homework.
I think you may be missing a subtle point here. +2C (relative to
pre-industrial) requires stabilisation in the region of 450ppm CO2, not
550ppm (which is doubling). Of course there is uncertainty due to
uncertainty in climate sensitivity, but these are probably reasonable
ballpark figures. Given that we are at 430ppm CO2 equivalent, and 380ppm
CO2 alone (and rapidly rising), the lower target is pretty hard!
James
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