Text 11972, 69 rader
Skriven 2007-02-10 04:48:41 av Shabaz (15413.babylon5)
  Kommentar till text 11937 av rec.arts.sf.tv.babylon5.moderated (15378.babylon5)
Ärende: Re: Global warming, among other things
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On Feb 10, 2:49 am, Josh Hill <userepl...@gmail.com> wrote:
> Unfortunately, the IPCC's statement about sea levels was obsolete even
> before it was published, because they ignored the latest data on ice
> melting.
They didn't really "ignore" it. They very explicitly mention that they
did not include these, and gave an explanation why, which I'm just
going to quote in its entirety:

>>Models used to date do not include uncertainties in climate-carbon cycle
feedback nor do they include the full effects of changes in ice sheet flow,
because a basis in published literature is lacking. The projections include a
contribution due to increased ice flow from Greenland and Antarctica at the
rates observed for
1993-2003, but these flow rates could increase or decrease in the
future. For example, if this contribution were to grow linearly with
global average temperature change, the upper ranges of sea level rise
for SRES scenarios shown in Table SPM-2 would increase by 0.1 m to 0.2
m. Larger values cannot be excluded, but
understanding of these effects is too limited to assess their
likelihood or provide a best estimate or an upper bound for sea level
rise. {10.6}<<

And they mentioned, again, explicitly, later in the SPM that while
there wasn't enough understanding to say anything about the magnitude,
recent observations do suggest ice flow dynamics could lead to further
sea level rise:

>>Dynamical processes related to ice flow not included in current models but
suggested by recent observations could increase the vulnerability of the ice
sheets to warming, increasing future sea level rise. Understanding of these
processes is limited and there is no consensus on their magnitude. {4.6,
10.7}<<

The IPCC is usually conservative in its conclusions, and errs on the
side of not overstating certainty levels, which is the most
scientifically valid way to go, I think. Despite that, they made
absolutely clear that their projections did not include these things,
made clear why they weren't included, and did explicitly mention what
the recent data, while not sufficient to draw conclusions on the
certainty level that the IPCC required, pointed at. Their job is not
to do new science per se, but to assess the current state of science
and synthesise it, and draw conclusions if there is a consensus to
back that up. I think they did a reasonable job doing that in the
SPM.

And I'm sure that the full AR4 WG1 report will contain more detailed
deliberations on these dynamics and assessments of the now current
science on it that is out there. Which, like the full IPCC reports in
general, will still make it an incredibly useful tool for scientists
to reference on the topic, and I don't think it necessarily will be
"obsolete" in that respect.

>  But in that event, he
> said, they should make it known that their estimates did not include
> factors like ice sheet movement and collapse, which appear to be
> accelerating.'

This is pretty much exactly what they ended up doing. Read the AR4 SPM
page 11 and how they for instance label the sea rise column of the
SPM-2 table, or what they state in the bullet point directly
underneath the table, and you'll see they make it pretty darn explicit
that this wasn't included in the number. Now, obviously this
particular detail has been subject to quite a bit of confusion in the
media, which is regrettable, but it's pretty hard to miss if you read
the actual SPM.

-Shabaz
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