Climate sensitivity of 8-10C can't be ruled out
gerh...@aston.ac.uk
Transient climate-carbon simulations of planetary geoengineering
H. Damon Matthews and Ken Caldeira
"If climate sensitivity turns out to be on the high end of current
estimates [which have not been able to rule out climate sensitivities
as large as 8-10°C for a doubling of CO2 (e.g., ref. 15)], ..."
Published online before print June 4, 2007, 10.1073/pnas.0700419104
PNAS | June 12, 2007 | vol. 104 | no. 24 | 9949-9954
OPEN ACCESS ARTICLE
William M Connolley
On Mon, 18 Jun 2007, gerh...@aston.ac.uk wrote:
> "If climate sensitivity turns out to be on the high end of current
> estimates [which have not been able to rule out climate sensitivities
> as large as 8-10°C for a doubling of CO2 (e.g., ref. 15)], ..."
You're just trying to wind James up, aren't you?
-W.
William M Connolley | w...@bas.ac.uk | http://www.antarctica.ac.uk/met/wmc/
Climate Modeller, British Antarctic Survey | 07985 935400
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Michael Tobis
of MIT, home of Dick "what-me-worry?" Lindzen.
They have anticipated James' response, I expect:
"When using unifrom priors on all parameters, these new results are
summarized by the 90% confidence bounds of 2.1 to 8.9 K for climate
sensitivity... We note that the upper bound for the climate
sensitivity is sensitive to our choice fo prior, which was truncated
at 10 K. WHen an expert prior for S is used [Forest et al 2002
(Science 295 113-117)] the 90% confidence intervals are 1.9 to 4.7
K... for S... "
All this amounts to is that the dataset in question is insufficient to
constrain S very well. If you really want to know S, you use
allavailable information, which can be embodied in an expert prior. A
non-truncated prior is mathematically unworkable, and a truncated
prior just amounts to a particularly foolish choice of prior. The high
end you get back out (in this case 8.9 K) is pretty much the same as
the high end you put in (10 K) and tells you nothing.
Note the following in the concluding paragraph
"Despite their uncertainties, the paleoclimate results provide data
not directly included in the present framework... and this supports
using a prior influenced by such results."
This is clear enough to the peer audience, but that group is very
narrow, and it seems likely that Matthews and Caldeira are not in it..
I think this raises important questions about intra-scientific
communication, but I don't think it means we need to worry about a 9 C
sensitivity.
In other words, just because you can't tell by looking at the clouds
whether it is Tuesday does not make the day of the week unknown. It
just means that information is not encoded very clearly in the clouds.
One trouble with science is that stuff gets misused by non-target
audiences. I see no reason to believe that Forest is actually worried
about a nine degree sensitivity on the basis of this paper.
As far as nonstatisticians are concerned, it pretty much looks like
it's 3 C or a smidge under. Can we move on please?
mt
Tom Adams
Perhaps its a good time for me to ask about something I have been
wondering about.
Does this concept of "climate sensitivity" (currently estimated at 3 C
per doubling of CO2) have a tight definition?
I assume it is meant to apply no just to the doubling of CO2 but to
the doubling of CO2 equivalence of all greenhouse gases?
Seems to me (the non-expert) that it takes into account some feedbacks
but not all? I think it includes water vapor, correct? But is it
meant to include every feedback? Albedo, etc. ?
Seems that it could not include the feedback where heating releases
more greenhouse gases from the permafrost and other places since the
level of CO2 (or equivalent) is apparently already built into the
definition. On the other hand, if you are looking at data on the
history of the climate (history of temperature and greenhouse gas
levels), then that data would seem to include all the feedbacks. Is
there (or should there be) another definition of climate sensitivity
that includes all the feedbacks?
Michael Tobis
> Perhaps its a good time for me to ask about something I have been
> wondering about.
>
> Does this concept of "climate sensitivity" (currently estimated at 3 C
> per doubling of CO2) have a tight definition?
Yes. It essentially is about the equilibrium response of the
atmosphere-ocean-sea-ice system, given a carbon input. Ice sheet
dynamics is explicitly left out. I am not sure how surface albedo and
evapotranspiration are coupled in these models; in the real world
these can be important locally but are unlikely to be a first order
global effect.
Most importantly, carbon cycle coupling is presumed to be part of the
forcing, though; it is taken as given in evaluating "the" sensitivity.
There are efforts underway to change this, to drive the models from
emissions and land usage, and couple land and ocean carbon feedbacks
explcitly. I
'm personally very unconvinced that the huge effort toward gearing up
to very fine scale coupled carbon-cycle/climate models (called ESM or
an Earth System Models) is timely either scientifically or as a source
of practical advice to the policy sector. Note, though, that I am so
much an outlier on this topic that I don't even think it is worth
fighting about just now. Once the outputs of these models start to
appear there will be more basis for discussing how reliable and useful
they are. There is too much institutional momentum right now to bother
making the case against building them.
> I assume it is meant to apply no just to the doubling of CO2 but to
> the doubling of CO2 equivalence of all greenhouse gases?
I think that's right.
> Seems to me (the non-expert) that it takes into account some feedbacks
> but not all? I think it includes water vapor, correct?
> But is it
> meant to include every feedback?
No. The "climate system" is the atmosphere, ocean and sea ice. Land
surface process changes, again, are a grey area.
> Albedo, etc. ?
Again, I am not sure how albedo coupling from land surfaces is
treated. A good question, but probably not a first order question on
the global scale.
> Seems that it could not include the feedback where heating releases
> more greenhouse gases from the permafrost and other places since the
> level of CO2 (or equivalent) is apparently already built into the
> definition. On the other hand, if you are looking at data on the
> history of the climate (history of temperature and greenhouse gas
> levels), then that data would seem to include all the feedbacks. Is
> there (or should there be) another definition of climate sensitivity
> that includes all the feedbacks?
This is a very nicely framed question. There is a more or less
sensible answer but it's subtle.
More to follow. Meanwhile, does anyone else care to take this up?
mt
William M Connolley
Anyone read the latest Hansen in Proc Roy Soc:
http://pubs.giss.nasa.gov/docs/2007/2007_Hansen_etal_2.pdf
Anyone believe it?
William M Connolley
On Tue, 19 Jun 2007, Michael Tobis wrote:
> On 6/19/07, Tom Adams <tada...@yahoo.com> wrote:
>> Does this concept of "climate sensitivity" (currently estimated at 3 C
>> per doubling of CO2) have a tight definition?
Wot the IPCC mean by it is at http://www.grida.no/climate/ipcc_tar/wg1/518.htm
with ref to chapter 9.
Although this (as mt says) is generally assumed to leave out e.g. ice sheet
response, it could be argued to be ambiguous: it sez: "The .equilibrium climate
sensitivity. (IPCC 1990, 1996) is defined as the change in global mean
temperature, T2x, that results when the climate system, or a climate model,
attains a new equilibrium with the forcing change F2x resulting from a doubling
of the atmospheric CO2 concentration" which appears to mean that it cinludes
anything that happens to be within your model.
Phil Randal
> Anyone read the latest Hansen in Proc Roy Soc:
>
> http://pubs.giss.nasa.gov/docs/2007/2007_Hansen_etal_2.pdf
>
> Anyone believe it?
>
> -W.
>
> William M Connolley | w...@bas.ac.uk |http://www.antarctica.ac.uk/met/wmc/
> Climate Modeller, British Antarctic Survey | 07985 935400
This story was the entire front page of today's "Independent":
http://environment.independent.co.uk/climate_change/article2675747.ece
Phil
Michael Tobis
ones I had heard before, but overall the whole picture is in line with
how I understand it, yes. This understanding is based on lurking
around midwestern paleoclimatologists of late.
Paleo is not my own background, and they shouldn't be held responsible
for the extent to which I remain confused.
That said, to me what Hansen says appears more or less in proportion
with the standard paeloclimatologist / paleoglaciologist position.
Though there remains some disagreement on details, the expectation
that we are almost surely in for a very bumpy ride for centuries and
probably millenia as a consequence of current activity is not, in my
opinion, controversial in those circles.
Can I take it that you disagree?
mt
Coby Beck
"William M Connolley" <w...@bas.ac.uk> wrote in message
news:<Pine.LNX.4.64.07...@localhost.localdomain>...
>
>
> Anyone read the latest Hansen in Proc Roy Soc:
>
> http://pubs.giss.nasa.gov/docs/2007/2007_Hansen_etal_2.pdf
>
> Anyone believe it?
>
I believe it, at least the first few pages. Do you? And if not what
specifically and why?
Coby
William M Connolley
On Tue, 19 Jun 2007, Coby Beck wrote:
>> http://pubs.giss.nasa.gov/docs/2007/2007_Hansen_etal_2.pdf
>>
>> Anyone believe it?
>
> I believe it, at least the first few pages. Do you? And if not what
> specifically and why?
I don't think the implication of probable rapid sea-level rise by 2100, from
analogies with the palaeo record, is supportable.
(thats an answer to mt too).
Michael Tobis
km behing a sub-sea-level ridge it is currently resting upon, there's
a scenario which can't be eliminated whereby about a quarter of the
WAIS turns into a huge relatively fast flowing glacier leading to as
much as 2 meters sea level rise on a time scale on the order of a
century. It would be like popping a cork on a bottle; the ice sheet
would just spill out the opening.
This is summarized in Hansen's "rising sea level helps unhinge the ice
from pinning points".
I'm not sure this is regarded as likely, but it at least it's not very unlikely.
The quaternary record does indeed show abrupt warmings and sea level
rises, and recent observations have revealed new mechanisms of abrupt
ice failure.
Why should we be immune to abrupt failures of ice sheets. They have
happened in the past.
In what way is the analogy to the paleo record unsupportable?
I think Hansen carefully avoided quantitative predictions. Informally
speaking, over a meter of sea level rise in excess of thermal
expansion, in this century, is not at all off the table from what I am
hearing from people whose business it is to think about this problem.
I am sure you hear from others, but I don't know why they or you feel
confident in discounting this.
mt
Tom Adams
> On Tue, 19 Jun 2007, Coby Beck wrote:
> >>http://pubs.giss.nasa.gov/docs/2007/2007_Hansen_etal_2.pdf
>
> >> Anyone believe it?
>
> > I believe it, at least the first few pages. Do you? And if not what
> > specifically and why?
>
> I don't think the implication of probable rapid sea-level rise by 2100, from
> analogies with the palaeo record, is supportable.
>
> (thats an answer to mt too).
I don't think that was his whole argument.
As far as I know from your reply above, you may well be completely
convinced by the physics of albedo, even if you don't think the paleo
record is a slam dunk.
Also, the physics/earth science of albedo is something to study,
measure, all that. Seems a good scientific paper from the standpoint
of lots of stuff there to try to refute.
I assume you are saying the paleo record is ambiguous on the matter?
Or are you saying the evidence points the other way?
SCM
On Jun 20, 8:26 am, Tom Adams <tadams...@yahoo.com> wrote:
> On Jun 19, 5:02 pm, William M Connolley <w...@bas.ac.uk> wrote:
>
> > On Tue, 19 Jun 2007, Coby Beck wrote:
> > >>http://pubs.giss.nasa.gov/docs/2007/2007_Hansen_etal_2.pdf
>
> > >> Anyone believe it?
>
> > > I believe it, at least the first few pages. Do you? And if not what
> > > specifically and why?
>
> > I don't think the implication of probable rapid sea-level rise by 2100, from
> > analogies with the palaeo record, is supportable.
>
> > (thats an answer to mt too).
>
I was struck by the strong language used in the paper (and borrowed
for the Independent headline):
"(d ) Planet Earth today: imminent peril
The imminent peril is initiation of dynamical and thermodynamical
processes
on the West Antarctic and Greenland ice sheets that produce a
situation out of
humanity's control..."
Hansen is certanly abandoning the scientific reticence he complained
about previously.
What I want to know though (from the climate scientists preferably) is
can you rule this idea of Hansen et al out?
William M Connolley
On Tue, 19 Jun 2007, Michael Tobis wrote:
> If I understand correctly, if the Thwaite Glacier retreats a couple of
> km behing a sub-sea-level ridge it is currently resting upon, there's
> a scenario which can't be eliminated whereby about a quarter of the
> WAIS turns into a huge relatively fast flowing glacier leading to as
> much as 2 meters sea level rise on a time scale on the order of a
> century. It would be like popping a cork on a bottle; the ice sheet
> would just spill out the opening.
>
> This is summarized in Hansen's "rising sea level helps unhinge the ice
> from pinning points".
>
> I'm not sure this is regarded as likely, but it at least it's not very unlikely.
Is it "can't be eliminated" or " not very unlikely" or what? Really quite
improbable would be my view. I don't think ice sheet behave like champagne. But
since H isn't saying this, we're getting a bit off track.
> The quaternary record does indeed show abrupt warmings and sea level
> rises, and recent observations have revealed new mechanisms of abrupt
> ice failure.
>
> Why should we be immune to abrupt failures of ice sheets. They have
> happened in the past.
>
> In what way is the analogy to the paleo record unsupportable?
The idea that it supports his predictions of less than century-timescale rapid
sea level rise.
> I think Hansen carefully avoided quantitative predictions. Informally
> speaking, over a meter of sea level rise in excess of thermal
> expansion, in this century, is not at all off the table from what I am
> hearing from people whose business it is to think about this problem.
>
> I am sure you hear from others, but I don't know why they or you feel
> confident in discounting this.
As you say, H is a bit vague on the quant side. I'm disliking his language
mostly: "Recent greenhouse gas (GHG) emissions place the Earth perilously close
to dramatic climate change that could run out of our control, with great
dangers for humans and other creatures."
or,
"Our concern that BAU GHG scenarios would cause large sea-level rise this
century (Hansen 2005) differs from estimates of IPCC (2001, 2007), which
foresees
little or no contribution to twenty-first century sea-level rise from Greenland
and
Antarctica. However, the IPCC analyses and projections do not well account for
the
nonlinear physics of wet ice sheet disintegration, ice streams and eroding ice
shelves,
nor are they consistent with the palaeoclimate evidence we have presented for
the
absence of discernable lag between ice sheet forcing and sea-level rise."
-W.
> mt
William M Connolley
On Tue, 19 Jun 2007, Tom Adams wrote:
> On Jun 19, 5:02 pm, William M Connolley <w...@bas.ac.uk> wrote:
>> On Tue, 19 Jun 2007, Coby Beck wrote:
>>>> http://pubs.giss.nasa.gov/docs/2007/2007_Hansen_etal_2.pdf
>>
>>>> Anyone believe it?
>>
>>> I believe it, at least the first few pages. Do you? And if not what
>>> specifically and why?
>>
>> I don't think the implication of probable rapid sea-level rise by 2100, from
>> analogies with the palaeo record, is supportable.
>>
>> (thats an answer to mt too).
>
> I don't think that was his whole argument.
Errrm, what else does he have to say then?
> As far as I know from your reply above, you may well be completely
> convinced by the physics of albedo, even if you don't think the paleo
> record is a slam dunk.
>
> Also, the physics/earth science of albedo is something to study,
> measure, all that. Seems a good scientific paper from the standpoint
> of lots of stuff there to try to refute.
If you strip out the emotive language, yes.
> I assume you are saying the paleo record is ambiguous on the matter?
> Or are you saying the evidence points the other way?
H seems to be translating absence of discernable lag between ice sheet forcing
and sea level rise from the palaeo stuff into a likelihood of 2m of SLR this
century. I don't think you get century-scale info out; and anyway the general
view os for a ~800 year lag from forcing to response.
-W
Alastair McDonald
----- Original Message -----
From: "William M Connolley" <w...@bas.ac.uk>
To: <global...@googlegroups.com>
Sent: Tuesday, June 19, 2007 4:41 PM
Subject: [Global Change: 1757] Latest Hansen
>
>
> Anyone read the latest Hansen in Proc Roy Soc:
>
> http://pubs.giss.nasa.gov/docs/2007/2007_Hansen_etal_2.pdf
>
> Anyone believe it?
Yes!
But it is very difficult to argue against people like you and James who
scoff at the science.
Cheers, Alastair.
Janne Sinkkonen
> The idea that it supports his predictions of less than century-timescale rapid
> sea level rise.
He has been arguing for the possibility of rapid sea level rise in his
earlier papers -- I'm not able to qualify the evidence, though. But
given this, and his recent writings about the unwillingness of
scientists to communicate outcomes of AGW in emotive terms, there is
not much surprise here.
'Imminent peril' is not often seen in scientific publications, but on
the other hand it is not a precise term and does not therefore exactly
claim anything unsupportable. In the absence of quantitative
predictions, it is just coloring. I find it personally quite
entertaining, and a bit worrying of course.
--
Janne
Tom Adams
Don't we know a good bit about the emergence from the last ice age?
In a book about the prehistory of Scotland "Beyond Scotland" it
mentioned that the sea level rose a meter or so (or was it a foot?) in
a few days, causing a good bit of havoc for the humans living along
the coast of the land bridge between Scotland and Europe. Due to an
ice dam failing or a meteor impact hiting Canada's glacier or
something. If we have archeological data about impact of sea level
rise on humans, then, with all the other potential data, I'd think we
might be able to map it out in time pretty well.
I wonder if there is evidence about albedo flip one way or the other
from the last ice age?
>
> -W
>
>
>
> >> -W.
>
> >> William M Connolley | w...@bas.ac.uk |http://www.antarctica.ac.uk/met/wmc/
> >> Climate Modeller, British Antarctic Survey | 07985 935400
>
> >> --
> >> This message (and any attachments) is for the recipient only. NERC is subject
> >> to the Freedom of Information Act 2000 and the contents of this email and any
> >> reply you make may be disclosed by NERC unless it is exempt from release under
> >> the Act. Any material supplied to NERC may be stored in an electronic
> >> records management system.
>
> William M Connolley | w...@bas.ac.uk |http://www.antarctica.ac.uk/met/wmc/
> Climate Modeller, British Antarctic Survey | 07985 935400
>
> --
> This message (and any attachments) is for the recipient only. NERC is subject
> to the Freedom of Information Act 2000 and the contents of this email and any
> reply you make may be disclosed by NERC unless it is exempt from release under
> the Act. Any material supplied to NERC may be stored in an electronic
> records management system.- Hide quoted text -
>
> - Show quoted text -
William M Connolley
On Wed, 20 Jun 2007, Tom Adams wrote:
> In a book about the prehistory of Scotland "Beyond Scotland" it
> mentioned that the sea level rose a meter or so (or was it a foot?) in
> a few days, causing a good bit of havoc for the humans living along
> the coast of the land bridge between Scotland and Europe. Due to an
> ice dam failing or a meteor impact hiting Canada's glacier or
> something. If we have archeological data about impact of sea level
> rise on humans, then, with all the other potential data, I'd think we
> might be able to map it out in time pretty well.
The meteor idea would suggest that palaeo analogues are even less useful!
-W.
Tom Adams
> On Tue, 19 Jun 2007, Tom Adams wrote:
> > On Jun 19, 5:02 pm, William M Connolley <w...@bas.ac.uk> wrote:
> >> I don't think the implication of probable rapid sea-level rise by 2100, from
> >> analogies with the palaeo record, is supportable.
> > I don't think that was his whole argument.
> Errrm, what else does he have to say then?
The other key part of his argument is:
"IPCC (2001, 2007) foresees twenty-first century sea-level rise of
only a fraction of
a metre with BAU global warming. Their analysis assumes an inertia for
ice
sheets that, we argue, is ... inconsistent
with observations of current ice sheet behaviour."
"existing ice sheet models are missing
realistic (if any) representation of the physics of ice streams and
icequakes,
processes that are needed to obtain realistic nonlinear behaviour."
"...the IPCC analyses and projections do not well account for the
nonlinear physics of wet ice sheet disintegration, ice streams and
eroding ice
shelves..."
Do you believe that part?
Tom Adams
> On Wed, 20 Jun 2007, Tom Adams wrote:
> > In a book about the prehistory of Scotland "Beyond Scotland" it
> > mentioned that the sea level rose a meter or so (or was it a foot?) in
> > a few days, causing a good bit of havoc for the humans living along
> > the coast of the land bridge between Scotland and Europe. Due to an
> > ice dam failing or a meteor impact hiting Canada's glacier or
> > something. If we have archeological data about impact of sea level
> > rise on humans, then, with all the other potential data, I'd think we
> > might be able to map it out in time pretty well.
>
> The meteor idea would suggest that palaeo analogues are even less useful!
I guess you are right that even if we could identify a rapid sea level
rise event in the paleo record we could no just assume it's due to
albedo flip.
But I was thinking that we might know more about the rate of the last
big thaw, the whole thaw, not just that one event that may have been
caused by a meteor or ice damn break.
Tom Adams
> On Tue, 19 Jun 2007, Coby Beck wrote:
> >>http://pubs.giss.nasa.gov/docs/2007/2007_Hansen_etal_2.pdf
>
> >> Anyone believe it?
>
> > I believe it, at least the first few pages. Do you? And if not what
> > specifically and why?
>
> I don't think the implication of probable rapid sea-level rise by 2100, from
> analogies with the palaeo record, is supportable.
But that is not what he said. He said that the notion of ~800-year
lag in sea level rise is not supportable in the paleo record. I
think he's saying that you can't support any lag in the paleo record,
right?
Of course there is some lag. But, if he is right, you'd have to
estimate it from something other than the paleo record. You'd have to
estimate it from observations from a more recent period or from first
principles. Or take a shot at getting more data on one or more ice
age thaws.
Nowhere did he imply that rapid sea-level rise is supported by the
paleo record. I know that its easy to miss this since he talks about
what happen if the IPCC is wrong about an ~800-year lag. He sows
seeds of doubt about the IPCC take on rate sea level rise. Then he
speculates, spins a yarn, about what happened, and that yarn is not
supported (or refuted) by the evidence.
He is saying that the paleo record does not support any lag and the
physics of ice melting does not support a lag sufficient to get the
IPCC off thin ice.
He's trying knock down all the supports under your belief in a ~800-
year lag. And the IPCC's belief.
So, what is the support for the ~800-year lag notion? I there any?
Michael Tobis
> On Tue, 19 Jun 2007, Michael Tobis wrote:
> > It would be like popping a cork on a bottle; the ice sheet
> > would just spill out the opening.
> >
> > This is summarized in Hansen's "rising sea level helps unhinge the ice
> > from pinning points".
> >
> > I'm not sure this is regarded as likely, but it at least it's not very unlikely.
>
> Is it "can't be eliminated" or " not very unlikely" or what? Really quite
> improbable would be my view. I don't think ice sheet behave like champagne. But
> since H isn't saying this, we're getting a bit off track.
I don't say it behaves like champagne, but it does behave like
ketchup. It's very viscous, but it does flow. Viscous flow flux
depends crucially on the width of the flow. A very wide stream of
ketchup can pour quite quickly, as can a very wide glacier. It can
also statically sustain a gravitational gradient at the margins. Such
a condition can switch suddenly from a static to a dynamic state with
small changes in boundary conditions.
The question is whether an Antarctic basin which rests on a
sub-sea-level floor can fail in a very large glacierlike flow mode.
Greenland has to fail by icequakes and moulins and lots of messy
stuff, but the West Antarctic simply has to find an outlet and spill
out of it. This is almost certainly the failure mode of ice sheets
that rest on the sea floor. The WAIS is the only remaining bit of
those, and it apparently did disappear for the most part in the
previous interglacial, indicating that its state is precarious
already.
Right now it's pinned up against a ridge. If the edge gets slushy and
it retreats behind the ridge, it's not a matter of warming the
interior for it to fail. Gravity is sufficient, though warming will
just make it worse.
The edge is in fact getting slushy, more than local warming would
account for. There are arguments as to why; someone has even tried to
implicate the ozone hole as a player I hear.
So what constrains the maximum mass flux through an unplugged glacier
with a 2 km gravitational head and a several hundred kilometer outlet
width? The impassioned answer is "not much".
The dispassionate answer is "dynamics for which we have no adequate
quantitative model". Which is to say, 800 years, 100 years, these are
pretty close to each other dynamically but pretty far apart in
practical impact. I've only just started to hang around with ice
experts, so my own intuitive guess is sufficiently worthless that I
probably shouldn't mention it.
It is, in fact, quite a serious matter to say that the 100 year 2
meter rise can't be excluded on current evidence. It would be good if
we could do a better job of quantifying this, but insofar as we have
very little observational evidence to constrain the model it does seem
prudent to treat a 2 meter rise in a century as a substantial
possibility. (With a "bigger than 10%" feel in that IPCC-ish
qualitative probability range space.)
Then there's Greenland...
I agree that there is more than a hint of polemics in the
presentation, but I'm not at all convinced that it's inappropriate
given the seriousness of the situation. I don't think anything Hansen
said is substantively out of line with current knowledge.
Have you looked at the possibility of WAIS collapse by super-glacier
dynamics? On what basis, dynamic or observational, do you either a)
constrain the time scale to greater than a century or b) discount the
possibility?
Hansen is questioning the conventional wisdom. "I don't think so"
doesn't constitute a strong defense, especially given that the actual
substantive content of AR4 is "we don't know, really".
mt
William M Connolley
On Wed, 20 Jun 2007, Tom Adams wrote:
> "IPCC (2001, 2007) foresees twenty-first century sea-level rise of
> only a fraction of
> a metre with BAU global warming. Their analysis assumes an inertia for
> ice
> sheets that, we argue, is ... inconsistent
> with observations of current ice sheet behaviour."
Observations, excluding the last few years, would tell us not to expect anything
very exciting. Adding in the last few years could get you excitement, if you
were to expect the acceleration in greenland to continue, as long as you
discounted the most recent ones showing a decline.
> "existing ice sheet models are missing
> realistic (if any) representation of the physics of ice streams and
> icequakes,
> processes that are needed to obtain realistic nonlinear behaviour."
>
> "...the IPCC analyses and projections do not well account for the
> nonlinear physics of wet ice sheet disintegration, ice streams and
> eroding ice
> shelves..."
>
> Do you believe that part?
Those bits are missing, indeed. Which means we really don't know what effects
they might have. And neither does Hansen. And, of course, the bulk of W Ant will
not get wet.
James Annan
> On Jun 20, 9:43 am, William M Connolley <w...@bas.ac.uk> wrote:
>> On Wed, 20 Jun 2007, Tom Adams wrote:
>>> In a book about the prehistory of Scotland "Beyond Scotland" it
>>> mentioned that the sea level rose a meter or so (or was it a foot?) in
>>> a few days, causing a good bit of havoc for the humans living along
>>> the coast of the land bridge between Scotland and Europe. Due to an
>>> ice dam failing or a meteor impact hiting Canada's glacier or
>>> something. If we have archeological data about impact of sea level
>>> rise on humans, then, with all the other potential data, I'd think we
>>> might be able to map it out in time pretty well.
>> The meteor idea would suggest that palaeo analogues are even less useful!
>
> I guess you are right that even if we could identify a rapid sea level
> rise event in the paleo record we could no just assume it's due to
> albedo flip.
>
> But I was thinking that we might know more about the rate of the last
> big thaw, the whole thaw, not just that one event that may have been
> caused by a meteor or ice damn break.
Don't forget that when you are looking at the paleo record (especially
termination of the last ice age) you are talking about a time when there
were large ice sheets at relatively modest latitudes, which can soak up
a whole lot of rays. There simply isn't this ice to melt any more.
I've spent some time looking at climate sensitivity and believe that I'm
on solid ground there. I'm reluctant to wade in over Hansen and ice
sheets because I know much less about them, but the argument seems to
follow a similar meme: we "can't rule it out", so we should worry. I'm
also a bit dubious about the language in any case: it's not as if people
are going to be drowned in their beds.
The time I would look for analogues is the last interglacial, when it
was significantly warmer than today. If there is any catastrophic
nonlinearity, one might expect there to have been a rapid sea level rise
at that time. I'm dubious about this having happened, because if there
was a rapid collapse on the 100 year time scale, one might reasonably
also expect a larger long-term change than was seen in practice. But I
don't know how good the data are.
James
Tom Adams
Wrong!
One word: nawlins
People will drowned and the last part ain't slow.
I think those in the nursing homes did drown in their bed.
Where did most of the young ones drown? In their attics?
>
> The time I would look for analogues is the last interglacial, when it
> was significantly warmer than today. If there is any catastrophic
> nonlinearity, one might expect there to have been a rapid sea level
> rise
Seems like a good point.
> at that time. I'm dubious about this having happened, because if there
> was a rapid collapse on the 100 year time scale, one might reasonably
> also expect a larger long-term change than was seen in practice. But I
> don't know how good the data are.
It was about 125K years ago.
Look at this plot:
http://en.wikipedia.org/wiki/Ice_age#Glacials_and_interglacials
Looks like it take 10K years to thaw and 100K years to refreeze.
The last thaw looks steeper at the end than this one, but maybe
that is a artifact of comparing near term measurements with 125K years
ago. And, of course it tells you nothing about the finer grain rates.
>
> James- Hide quoted text -
James Annan
>> it's not as if people
>> are going to be drowned in their beds.
>
> Wrong!
>
> One word: nawlins
>
> People will drowned and the last part ain't slow.
>
I almost bothered to add the rider: "...unless they choose to live in a
city below sea level with inadequate defences" but I thought it sort of
went without saying...it's hardly a problem of sea level rise - the land
was subsiding far faster, and the levees were not maintained. One could
argue in a no less specious way that if sea level had been rising even
faster, they would probably have paid more attention to the risk, and
thus reduced it overall.
James
Tom Adams
Looking at the last few interglacials, I think I see evidence of the
lag:
http://en.wikipedia.org/wiki/Image:Ice_Age_Temperature.png
Look at all the temperature spikes. Some are narrow and some are
broad. Now look at the ice volume, the low ice volume minimums. The
ice volume minimums don't just reflect the maximum of the temperature
spikes, they also reflect the *width of the temperature spikes*.
That could only happen if there was a lag on the order of several
thousand years.
If you take the temperature plot and put it through a low pass filter
tuned to around 10K years, you would get the ice volume plot.
But that a kind of general lag. Our concern is the current
configuration of a particular ice sheet.
Alastair McDonald
What you are looking at there is the temperature in Antarctica. No one lives
there. Not even William :-). Nearly everyone, including William and James,
live in the Northern Hemisphere. For that you need the temperature record
from the Greenland ice cores. Here it one since the last interglacial. It
is the red oxygen isotope line at the top:
http://www.ncdc.noaa.gov/paleo/pubs/blunier2001/sync.pdf
I don't see many slow steady changes in that!
Cheers, Alastair.
>
>
> >
>
Tom Adams
On Jun 20, 12:59 pm, "Michael Tobis" <mto...@gmail.com> wrote:
> On 6/20/07, William M Connolley <w...@bas.ac.uk> wrote:
> It is, in fact, quite a serious matter to say that the 100 year 2
> meter rise can't be excluded on current evidence. It would be good if
> we could do a better job of quantifying this, but insofar as we have
> very little observational evidence to constrain the model it does seem
> prudent to treat a 2 meter rise in a century as a substantial
> possibility. (With a "bigger than 10%" feel in that IPCC-ish
> qualitative probability range space.)
I'm suprised no one is challenging you on that 10%. The upper
end of the IPCC consensus is .59 meters.
Michael Tobis
the number for now) *exclusive of changes of the main ice sheets* on
which they explicitly punted.
mt
Tom Adams
They did punt on that.
Aren't 2 meter per century melt pulses rare?
Particularly rare after 8 thousand years or so of stable temperatures?
Of course, the soot is a new problem.
To get to 10%, we would have to discover that we are on the verge of a
melt pulse, I think.
I agree that we need to study the heck of of the ice sheets, since it
is probable enough, and there is no known way to reverse it.
>
> mt
CobblyWorlds
I have to agree with William Connelly's words that it doesn't fully
demonstrate the inevitablility of SLR massively greater than IPCC
projections. But I've never read anything that totally rules it out,
so I don't agree with (what I perceive to be) his tone. That said I'm
an ex-sceptic enthusiast - not a modeller at the BAS. So whaddo-I-
know. ;)
We're not warming out of a glacial period, we're warming out of an
interglacial - the comparative lack of NH icecover seems to me to be a
significant enough factor to make direct analogy tricky (like some of
the MOC shutdown = new ice age stuff - zzzz). Albedo flip bothers me
more in cases like the Antarctic Peninsular, which seems to be a toe-
hold for this process onto the Antarctic continental periphery
(possibly removing the buttressing of the ice sheet in some limited
areas), rather than a major factor in global forcings to come.
The Hansen team's argument about spring forcing and it's implications
for rapid response to an increase of forcings seems reasonable, but I
don't see how it can then be extended to argumemts at resolutions of
less than a century.
I must admit that if I had to bet, I'd bet on the IPCC SLR results
underprojecting. But as the IPCC themselves state:
"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."(AR4
SPM).
So an acceptance of underprojection on this issue seems implicit in
what they say. There's not really much cause to suspect a negative
feedback from either ice-sheet or carbon cycle feedbacks.
In reality we're (globally) not going to do anything serious about
reducing emissions and other human impacts. And as Michael Tobis says
"years, 100 years, these are pretty close to each other dynamically
but pretty far apart in practical impact." So we'll find out in due
course.
If someone claims there's NO chance of a multi-metre SLR by 2100 I'd
be very interested in their reasoning. Because I doubt they could do
as well as Hansen's team has in reaching the opposite conclusion. I
just see doubt on both sides, and when facing a threat I have doubt
about, I take precautions assuming the worse.
gerh...@aston.ac.uk
> improbable would be my view. I don't think ice sheet[s] behave like champagne.
Just wondering, do you believe the 2C target is useful, and if so on
what basis? You don't seem to be buying the "ice sheets are going to
collapse by paleo analogy and so we are likely to see multi metre sea
level rise in 100-300 years" supporting point for one. You have been
good at confusing me about this. It's not that I agree/disagree with
you, I just don't understand what you actually believe.
On the one hand, you produce a post like this (Help me here defining
dangerous climate change):
http://scienceblogs.com/stoat/2007/05/help_me_here_defining_dangerou.php
and then you write that you've come to believe more and more that 2C
is a useful target, and that really costs don't matter given the
necessity of sticking to the target.
James Annan
> Quoting from
>
> Transient climate-carbon simulations of planetary geoengineering
>
> H. Damon Matthews and Ken Caldeira
>
> "If climate sensitivity turns out to be on the high end of current
> estimates [which have not been able to rule out climate sensitivities
> as large as 8-10°C for a doubling of CO2 (e.g., ref. 15)], ..."
That's nothing, some people are still touting absurd estimates, eg:
The regrets of procrastination in climate policy
Klaus Keller et al 2007 Environ. Res. Lett. 2 024004 (4pp)
doi:10.1088/1748-9326/2/2/024004
http://www.iop.org/EJ/abstract/1748-9326/2/2/024004
which uses the Andronove and Schlesinger 2001 result:
"At present, the most likely scenario is one that includes anthropogenic
sulfate aerosol forcing but not solar variation. Although the value of
the climate sensitivity in that case is most uncertain, there is a 70
percent chance that it exceeds the maximum IPCC value. This is not good
news." said Schlesinger.
(from <http://www.news.uiuc.edu/scitips/01/06globewarm.html>)
At least the Matthews and Caldeira approach is endorsed by the IPCC
authors, if not by me - this new paper deliberately cherry-picks an
extreme outlier to advance the case of mitigation...
James
William M Connolley
I don't know, is the honest answer. I don't think there is good evidence at the
moment that there are any clear "physical" dangerous things by 2100 - SLR being
the obvious. It seems more likely that biological type things might be a
problem. But I'm less well equipped to judge this, and have never seriously
studied it. Reading a bit, I've decided that the bio-problems stuff may be a bit
more firmly based than I'd thought. 2 oC appears to be somewhat arbitrary,
though.
-W.
Hank Roberts
I asked a while back in the 'Why Do Science in Antarctica' about some
of the reports --- remember 'Rapid Drumlin Formation'? at the time you
said you didn't know about it. I wondered who else at your shop might
know, since it seemed a rather dramatic bit of news that these
structures we've thought were longterm things could happen under the
ice and very fast.
So I guess my question back to you is, who at BAS is familiar with the
new reports about water and mud flow under the ice, outburst floods,
and such that underlies the new concerns? And where are they
publishing or blogging?
James Annan
I wouldn't read too much into one piece of research (and still less into
one journalist's report of same) but this does paint a picture of
relatively stable ice sheets (at least, Greenland):
http://news.bbc.co.uk/1/low/sci/tech/6276576.stm
James
Steve Bloom
James, given that the study discusses sharply different conditions in the
Eemian as contrasted with prior post-MPT interglacials and implies a much
greater contribution from the WAIS, "relatively stable" isn't quite the
phrase that comes to my mind. That second sentence seems frankly
misleading.
-- Steve Bloom
Greenland's ancient forests shed light on stability of ice sheet
Ice cores drilled from southern Greenland have revealed the first evidence
of a surprisingly lush forest that existed in the region within the past
million years. The findings from an international study published today in
the journal Science suggest that the southern Greenland ice sheet may be
much more stable against rising temperatures than previously thought.
Researchers analysed ice cores from a number of locations in Greenland,
including Dye 3 in the south of the country. From the base of the 2km deep
Dye 3 core, they were able to extract what they believe is likely to be the
oldest authenticated DNA obtained to date.
By analysing these DNA samples, the researchers identified a surprising
variety of plant and insect life, including species of trees such as alder,
spruce, pine and members of the yew family, as well as invertebrates related
to beetles, flies, spiders, butterflies and moths. The researchers believe
that the samples date back to between 450,000 and 800,000 years ago.
"We have shown for the first time that southern Greenland, which is
currently hidden under more than 2km of ice, was once very different to the
Greenland we see today," explains Professor Eske Willerslev, a Wellcome
Trust Bioarchaeology Fellow from the University of Copenhagen, who led the
study."Back then, it was inhabited by a diverse array of conifer trees and
insects."
The research implies that ancient forests covered southern Greenland during
a period of increased global temperatures, known as an interglacial period.
When temperatures fell again, the area became covered in ice. This ice sheet
appears to have remained during the last interglacial period
(116,000-130,000 years ago) when the temperature was 5°C warmer than today,
contrary to the view currently held by scientists. Professor Dorthe
Dahl-Jensen, also at the University of Copenhagen, has shown that in fact,
even during this interglacial period, the ice thickness at Dye 3 would have
been reduced to between 1 km to 1.5km.
"If our data is correct, then this means that the southern Greenland ice cap
is more stable than previously thought," says Professor Willerslev. "This
may have implications for how the ice sheets respond to global warming."
However, Professor Willerslev was keen to dismiss the idea that this meant
sea levels would not rise to the levels predicted by scientific models.
"We know that during the last interglacial, sea levels rose by 5-6m, but
this must have come from other sources additional to the Greenland ice cap,
such as Antarctic ice. I would anticipate that as the Earth warms from
man-made climate change, these sources would still contribute to a rise in
sea levels."
The results also show conclusively that ancient biomolecules from the base
of ice cores can be used by scientists to reconstruct the environments
hidden underneath ice-covered areas and can yield insights into the climate
and the ecology of communities from the distant past.
"Analysing ancient biomolecules from beneath glaciers and ice sheets is
challenging due to the very low concentrations, but the information is worth
the effort," says Dr Enrico Cappellini, a member of the University of York's
new PALAEO Group and another of the paper's co-authors, whose work is
supported by the European Commission. "Our study suggests a solution to this
problem. Given that ten per cent of the Earth's terrestrial surface is
covered by thick ice sheets, it could open up a world of new discoveries."
James Annan
> Eurekalert has a bit more interpretation from the authors (pasted below).
> James, given that the study discusses sharply different conditions in the
> Eemian as contrasted with prior post-MPT interglacials and implies a much
> greater contribution from the WAIS, "relatively stable" isn't quite the
> phrase that comes to my mind. That second sentence seems frankly
> misleading.
Which second sentence? Care to be a bit less cryptic?
James
Tom Adams
On Jun 26, 4:48 am, William M Connolley <w...@bas.ac.uk> wrote:
> On Sat, 23 Jun 2007, gerha...@aston.ac.uk wrote:
> >> Is [2m sea level rise this century] "can't be eliminated" or " not very unlikely" or what? Really quite
> >> improbable would be my view. I don't think ice sheet[s] behave like champagne.
>
> > Just wondering, do you believe the 2C target is useful, and if so on
> > what basis? You don't seem to be buying the "ice sheets are going to
> > collapse by paleo analogy and so we are likely to see multi metre sea
> > level rise in 100-300 years" supporting point for one. You have been
> > good at confusing me about this. It's not that I agree/disagree with
> > you, I just don't understand what you actually believe.
>
> > On the one hand, you produce a post like this (Help me here defining
> > dangerous climate change):
> >http://scienceblogs.com/stoat/2007/05/help_me_here_defining_dangerou.php
>
> > and then you write that you've come to believe more and more that 2C
> > is a useful target, and that really costs don't matter given the
> > necessity of sticking to the target.
>
> I don't know, is the honest answer. I don't think there is good evidence at the
> moment that there are any clear "physical" dangerous things by 2100 - SLR being
> the obvious. It seems more likely that biological type things might be a
> problem. But I'm less well equipped to judge this, and have never seriously
> studied it. Reading a bit, I've decided that the bio-problems stuff may be a bit
> more firmly based than I'd thought. 2 oC appears to be somewhat arbitrary,
> though.
Question for you and James:
If one plays the tape back from any possible dangerous climate
change, then is it not the case that we would be caught
flat-footed if we are not sufficiently precautionary? That
is, we will never prevent anything, or at least not till we run
out of cheap fossil fuels.
>
> -W.
>
> William M Connolley | w...@bas.ac.uk |http://www.antarctica.ac.uk/met/wmc/
> Climate Modeller, British Antarctic Survey | 07985 935400
>
> --
> This message (and any attachments) is for the recipient only. NERC is subject
> to the Freedom of Information Act 2000 and the contents of this email and any
> reply you make may be disclosed by NERC unless it is exempt from release under
> the Act. Any material supplied to NERC may be stored in an electronic
> records management system.- Hide quoted text -
Steve Bloom
pasted:
"The findings from an international study published today in the journal
Science suggest that the southern Greenland ice sheet may be much more
stable against rising temperatures than previously thought."
Given what the paper says, the above phrase seems to me to be more or less
saying "much more stable" = not guaranteed to melt before the WAIS. IMHO
"less predictable" or "potentially more persistent" would have better
captured the sense of the paper.
-- Steve
----- Original Message -----
From: "James Annan" <james...@gmail.com>
To: <global...@googlegroups.com>
James Annan
> James, I meant the second sentence from the Eurekalert press release I
> pasted:
>
> "The findings from an international study published today in the journal
> Science suggest that the southern Greenland ice sheet may be much more
> stable against rising temperatures than previously thought."
>
> Given what the paper says, the above phrase seems to me to be more or less
> saying "much more stable" = not guaranteed to melt before the WAIS. IMHO
> "less predictable" or "potentially more persistent" would have better
> captured the sense of the paper.
I guess it depends a bit on what one would claim was "previously
thought". AIUI the majority expectation has long been for a significant
melt on the multi-century time scale in the event of significant future
warming, although many would also admit the _possibility_ of something
more rapid. Hansen may be justified in drawing attention to this
possibility but I'm not aware of anyone having presented any real
evidence in favour of it. If one scores predictability in the natural
way as -\Sigma p \ln p then surely these results increase the
predictability (albeit perhaps not by much), since a relatively stable
ice sheet was already the standard view.
It is an interesting phenomenon to note how things can seem to become
more real merely through being talked about a lot, irrespective of
whether new evidences is presented.
James