Thaas outrageous, big Mammy refers. We had it as our journal club today, and the outcome was, no-one thought Hansen had done a convincing job.
The paper itself is confusing ("like being inside Hansens head", as someone put it) and its not clear what its really supposed to be about. My pdf attempts to understand it. The only slide that won't make sense is the last one; the 3-models-pic is number of AR4 models in the sresa1b scenario with sfc temperature in January above -5 oC. The conclusion of that (and other opinions in the room) is that substantial sfc albedo change is unlikely.
[Update: the original paper is here - thanks C -W]
[Update: there is some weirdness here about someone daring to reject Hansen for being 30 years out of date. But Phil Trans are not so bold -W]
Oh, I did read your paper, and it's that last part -- the albedo -- where I'm puzzled. You say I think that the models show no rapid change. I thought the models so far still include an assumption that the icecaps are stable long term? Or maybe I mean an assumption that there's no mechanism known? But I thought that's Hansen's point.
You write "as the ice cores show, the GHG forcing tops out at 280 in interglacials - something (unknown) stops this feedback from venting more CO2. Why do we expect more in the future?"
I'd thought the answer to that was 'rate of change' -- we're adding CO2 faster than all the known biogeochemical cycling has handled, however it may have happened, and we don't yet have a way to model the PETM excursion do we?
I've been remembering things like this -- 20 year old paper, but the recent sediment core work seems consistent with it. Yet the climate models don't include episodes of surging, as far as I know, and isn't that what Hansen's suggesting should be added?
"Marked changes in the surface-water hydrology of the Southern Ocean during the past 60 kyr ... From 35 to 17 kyr BP, the Southern Ocean polar front was covered by a melt-water lid containing a significant contribution from melting icebergs, calved from Antarctic ice shelves. These icebergs may have originated from a succession of surges of the ice shelves...."
More recent work was stuff like this:
Andrill, not yet published as far as I know
(just a snip, appears no longer available fulltext): Tarankai Daily News, New Zealand - Nov 18, 2007 ... the andrill drilling rig in antarctica's mcmurdo sound is capturing information ..."
".. the Larsen B Ice Shelf was a persistent presence throughout the Holocene, until its most recent collapse in March 2002. This observation is significant, indicating that modern climate perturbations in the region have had a greater impact on the Larsen B Ice Shelf than natural variability of the Holocene."
Thought there should be a link to the hansen paper in one of these posts. I assume it is
The references are indeed a bit cryptic, at least to someone like myself who isn't actively involved in the science. My take at simplification:
(1) Hansen believes strongly in the Albedo flip. Essentially the argument is that as an area of ice-cap transitions from accumulation zone to ablation zone, the (summertime) albedo decreases substantially. On a short time scale by melt-water & ice replacing snow, and on a longer scale, by the accumulation of impurities (dirt) present in the ice at the surface. The later effect is large for Alpine glaciers, but polar icecaps are much cleaner. How large is the second effect likley to be?
[For Antarctica, no-one believed that W Ant is liable to be melting significantly from above in the next century anyway, so its not very relevant. But, the air there is very clean so there would be little dust. Gr - dunno -W]
(2) The increase in meltwater penetrating to great depth will significantly weaken the resistance to flow and lead to rapid collapse. I think this is the true wildcard.
Do we have any decent data on basal slip versus meltwater supply?
(3) The CO2 concentration versus temperature lag is evidence that the time scale of temperature forcing to GHG change is of the order of a millenia. You express uncertainty that the geological evidence for this feedback is only valid for 180-280ppm, and extrapolation to current, and predicted levels is uncertain.
what about the argument, that in the past we had SLR of 5m/century (probably not the upper limit) during the glacial transition(s), while the forcing was much lower than current/predicted forcing.
[What of it? I don't think its an argument, its just an observation. The situation was different then. Even Hansen doesn't make it :-) -W]
What about the glacial Earthquakes, which are evidently increasing in number - http://tamino.wordpress.com/2007/03/30/greenland-tremors/
[Interesting, but again... what about them? Its a cause for uncertainty, but we have lots of uncertainty already. If you were going to act on uncertainty, you'd be acting now -W]
so basically what you're saying is that Hansen doesn't have any firm paleo evidence for what he's arguing ?
do you think he's deliberately trying to scare people, or what ?
[As far as I can tell, he has no firm evidence for what he is saying, although the paper is written in such a way that it can be hard to tell exactly what he (and of course his co-authors...) are claiming -W]
Is it acceptable to say a GHG feedback becomes a forcing?
Does that GHG feedback include H2O feedback?
If so, would that H2O feedback be greater than the CO2/CH4?
[On a long timescale, in principle I think its fine. H2O is such a fast feedback that its not the same issue -W]
Those of you wondering where JAmesG's post has come from can have a look at this thread over at TAmino's:
"[... If you were going to act on uncertainty, you'd be acting now -W]"
That's what I meant in the more recent thread; Hansen is thinking like a biologist now.
The introduction of the current level of uncertainty _is_ the evidence of the problem, for most biologists.
Climatologists who believe they share a consensus view of their own science might well -- like Hansen, I believe, is doing --- take advice from the biologists' older, and stronger, consensus view. For example:
There is little doubt left in the minds of professional biologists that Earth is currently faced with a mounting loss of species that threatens to rival the five great mass extinctions of the geological past. As long ago as 1993, Harvard biologist E.O. Wilson estimated that Earth is currently losing .... Some biologists have begun to feel that this biodiversity crisis -- this "Sixth Extinction" -- is even more severe, and more imminent, than Wilson had supposed...."
[If Hansen were talking about biology, I'd be happier. It looks to me as though most of the dangerious impacts of cl ch will be ecological. In this paper, Hansen tries to make them physical but, I think, fails -W]
Hansen wants to claim a doubling of climate sensitivity due to albedo changes from Antarctic ice melt. Maximum daytime summer elevation of the sun is 23.5 degrees. The sun doesn't shine at all on the continent for 4 months of the year. The ice sheet is km thick. And he wants us to believe that we're in danger of an runaway Antarctic-led albedo flip?
I tell you, the only thing thicker than the Antarctic ice is Hansen's skull. The guy is a complete idiot. Yet he's the designated leader of climatology.
Do you guys really wonder why we don't take your global warming claims seriously?
OK, Mugwump: Based on your doubtless extensive paleoclimate knowledge, what is the upper constraint on the pace of melt of either the GIS or WAIS?
Steve Bloom, I'll answer your question if you'll first explain its relevance, ie: how will marginal melting of the WAIS contribute 2X to climate sensitivity?
[Hint: think very thick ice, very low sun - try calculating the sine of 23.5 for starters. If you can manage that, see if you can work out the total yearly solar irradiation at the south pole compared to the equator based on the tilt of the Earth's axis (which, remarkably enough, is exactly the same as the maximum summer sun elevation at the south pole. Draw a picture, you should be able to get it. If not, grab a nearby 5th grader - they'll explain it to you).]
William, this paper's been around quite a while, and seems consistent with the reports of widespread surface melting on the poles -- though I don't recall any mention of widespread albedo change from those reports.
That seems the foundation argument -- that wet snow/ice absorbs heat better than dry.
Is that a safe assumption, or an empirical observation, or a conclusion from theory about wet vs. dry surfaces?
[Its the bleedin' obvious. What isn't obvious is that there is widespread melting at the poles -W]
I do see Hansen et al. making some leaps.
[I see nothing but leaps -W]
I'd guess the bottom line is that you disagree with this?
"If our interpretation of near synchroneity of forcing and ice sheet response is correct, implications for humanity are profound..."
If so, can you go through the basic reasoning of the paper and say what steps or cites fail to satisfy you?
[I doubt anyone could go through the basic reasonning, because it consists of nothing but leaps. Essentially, it appears to consist of the invalid inversion of "no multi-millenial lags" into "less than century effects" -W]
Can you be more specific about what you agree with, disagree with, or simply see no evidence for, going through the paper?
Remember I'm an amateur and just a reader, trying to ask questions because I need the help and others might.
They do the argument with many references to charts, and I'm thinking your doubts may be in what they infer from the charts -- if so what follows won't be useful unless you want to add more. I'm hoping you will.
Let me see if I can pick out their basic points -- and if I'm missing even that please correct me.
"Rapid warming at terminations, we assert, must be due to the fact that ice sheet disintegration is a wet process that, spurred by multiple thermodynamical and dynamical feedback processes (Hansen 2005), can proceed rapidly. Chief
among these feedbacks is the large change in absorbed solar energy that occurs with the 'albedo flip' when snow and ice become wet. This process determines the season at which insolation anomalies are most important.
"We suggest, however, that spring is the critical season for terminations, because the albedo feedback works via the large change in absorbed sunlight that begins once the ice/snow surface becomes wet, after which the surface albedo remains low until thick fresh snow accumulates."
"A spring maximum of insolation anomaly pushes the first melt earlier in the year, without comparable shortening of autumn melt, thus abetting ice sheet disintegration. And an increase of GHGs stretches the melt season both earlier and later, while also increasing midsummer melt. Thus, it is not surprising that Terminations I, II, III and IV all had strong maxima in GHG forcing, as well as, we presume, favourable insolation.
"Let us test 'the spring melt' proposition and examine consequences....
"... Confirmation of this interpretation of terminations requires additional accurately dated cases. Termination II, long an enigma owing to suggestions that the climate change preceded presumed orbital forcing, provides a stern test...."
"... available data for the two terminations with near-absolute dating do not provide evidence for multi-millennial lag between insolation forcing and ice sheet response. If our interpretation of near synchroneity of forcing and ice sheet response is correct, implications for humanity are profound."
["near syn" is deliberate mixing of ice-age and recent timescales. If the lags are long (measured in centuries) then the implications for humanity are not profound -W]
"Thick ice sheets provide not only a positive feedback, but also the potential for cataclysmic collapse, and thus an explanation for the asymmetry of the ice ages.
"The albedo flip property of ice/water provides a trigger mechanism. If the trigger mechanism is engaged long enough, multiple dynamical feedbacks will cause ice sheet collapse (Hansen 2005).
We argue that the required persistence for this trigger mechanism is at most a century, probably less. Global warming necessarily accompanies ice sheet loss and decreased surface albedo. Global warming, based on both palaeoclimate data and carbon cycle models, is accompanied by increased GHGs. The result is large global warming at terminations...."
[Its hard to know what to say. Its a mixture of well known stuff, some speculation, and a large amount of ambiguity as to what terms like "rapid" are supposed to mean. Try a test: what do *you* think he means by rapid? -W]
Here's an idiot's take on these issues. Discard as necessary.
Re: 280 ppm limit.
Doesn't CO2 ordinarily "top out" at 280 ppm, because, by then, the ice sheets of North America and Europe are spent. i.e. no more "easy" albedo changes, no more warming of the ocean.
Re: "few centuries"
The paper says this:
Note first that 'minor' mismatches in timing of observed and calculated temperatures in figure 2c are due to dating errors and, to a lesser degree, limitations of a local thermometer1. Proof is obtained by considering the contrary: ice sheet forcing approximately 3WmK2 and a 5 kyr timing gap between forcing and response, as appears to be the case at Termination IV (figure 2c), is 15 000Wyr mK2, enough to warm the upper kilometre of the ocean by approximately 1608C (see table S1 in Hansen et al. (2005b)). Obviously, no such warming occurred, nor did warming more than approximately 1/100th of that amount. Forcing and temperature change had to be synchronous within a few centuries, at most, for the large global climate change at terminations.
Re: "doubled" sensitivity
Hansen notes that the doubled "slow feedback" sensitivity from paleo climate doesn't include the additional GHG feedbacks that we are likely to see. And wouldn't the Laurentide icesheet, with so much of it within the interior of the continent be less dependent on butressing and sea level?
And doesn't Hansen respond to questions?
I'm sure Bill can properly answer about the differences between the Laurentide ice sheet, and the current GIS. The former was considerably larger, and yes further south. Wasn't it more or less centered where Hudson bay currently resides? Not only does this low flat topography lack the topological butressing of much of the GIS, but once portions could be floated on Hudsons bay, it was vulnerable to the sort of breakup observed with Larsen B. I suspect this (or something like it) argument is the origin of his statement about the relative stability of the two ice caps.
Hansen warns that during the breakup 5M/y of sealevel rise has been observed, implying we could experience a similarly rapid sealevel rise. Given the smaller surface area, and presumably higher stability of the GIS, presumably it won't supply meltwater at anything near that rate.
"Our primary interest in palaeoclimate rapid global warmings is their implication for twenty-first century climate change [p
This means they need to find processes operating within a century. I don't think they do. Statements like we find no evidence of
millennial lags between forcing and ice sheet response in palaeoclimate data [p1949] aren't good enough. ..." WC pdf
I don't agree with your take. I think he's saying rapid global warming episodes form the past have an implication for 21st century climate change in terms of what BAU may lock in for subsequent centuries, and that is when he's looking at processes operating within a century.
[I think his statement is perfectly clear: the interest is in cl ch over the 21st century. But if you think he is saying that the palaeo record tells you nothing interesting about cl ch over the 21st C itself, that too would be interesting -W]
Looks like a followup post got lost; briefly, I did read your paper William; the last point's the one I don't get; it's Hansen's first.
Where he writes:
"... albedo feedback works via the large change in absorbed sunlight that begins once the ice/snow surface becomes wet, after which the surface albedo remains low until thick fresh snow accumulates ..."
Is that radiation physics? Empirical observation? Speculation? Everything seems to turn on whether that's a correct statement, and whether surface meltwater does lead to water under the ice and movement and breakups.
Is any of albedo change with wet suface snow/ice, or meltwater from that, in any of the models now in use? I know the models now show no great changes, but do they include any of these ideas about how such might occur?
Hank, has zeroed in on the key arguments. I strongly believe wet snow has lower albedo than dry, but science, and especially modelling needs numerical values. The most important thing for his argument is to obtain actual albedo data, that can be plugged into the models.
[That wet snow has a lower albedo than dry is a commonplace. There are loads of studies of that kind of thing. The question is, what area of Antarctica is likely to be affected by this? The most likely answer is, not a lot, which is the point of my 3 pix on slide 4 -W]
The problem of what effect the meltwater has, is probably more difficult. A few years back we didn't think it could penetrate deeply (at least in dry (subfreezing)ice). We no longer think that is the case. Basal water probably accumulates, and releases episodically. I suspect it will take many years of observations before we have enough experience to even crudely model the effect of warming induced ice flow changes.
> what do you think he means by rapid?
I think he means -- for the past, and for the present -- the length of time over which climate forcings due to GHGs (CO2, CH4 and N2O) change during the past (thousands of years) (Fig. 2(b)).
[OK, then in that case we can ignore all his concerns about "rapid" climate change and "imminent" peril, because we have a thousnd years to prepare -W]
In the present, our baseline is, what, 11k years past the peak of one of those rapid changes, right? Just past the top of the natural rapid change peak.
We're adding, what, another 2x or 3x GHG to that and already have gone past the highest levels we've had while the continents were in their current positions, doing so at something like 100x the rate of change of natural rates.
Tell me if I'm getting these basic numbers wrong (hope someone from Dr. Hansen's team comments) -- I'm using the old Usenet approach, post what I understand and await correction).
[As I see it, we either adopt your reading of "rapid" - take it within the context of the ice age timescale, in which case its a few thousand years - in which case "rapid" climate change is nothing to worry about at all. Or, we read it to mean "less than a century", in which case we should worry, but in that case the palaeo stuff says nothing useful -W]
I think you need to accept both readings of "rapid" are possible, both are "fastest rate of change observed" --- "rapid" is defined by change in GHG, not by change in clock time.
[Of course both readings are possible. Thats the problem: Hansen fails to distingusih between two readings that very clearly need to be distinguished. Without this clear distinction you have meaningless mush -W]
I think they're saying "rapid" is the time required for a given rapid increase in GHG --- we have past rapid rises, and we have the current rise on top of the latest rapid rise.
We know some of the results of that much change in the past.
Hansen et al. anticipate similar changes from a similar increase in GHG amounts, but starting where we're at?
--- changes as seen in the past rapid events
--- closer to the poles as we're starting 'at the top' of a previous rapid event
--- at a rate of change related to rate of GHG increase
I'd been watching studies saying new things about rates of change, compared to the old "no change in thousands of years" idea about stability of the polar icecaps, for a while. I haven't seen any saying there won't be unanticipated fast change. Have you? (I cited some in your old "why Antarctica" thread, some in Pielke's "quarter inch" thread).
It's teaching kids about firebuilding, which most parents have to go through if their children are naturally inclined to experiment, and the parents want grandchildren:
We know firewood burns, open flame, or glowing coals.
We know what happens when we add twigs to coals.
We know what happens when we add paper to coals
We know what happens when we add candle wax to coals.
We know what happens when we add lamp oil to coals.
What can we expect if we add gasoline to coals?
We know what happens if we add twigs to open flame ....
Hansen et al. point to the past three rapid rises in GHG and to the known outcomes.
Then they point to the current rapid rise in GHG, on top of the last of the natural rises, and suggest outcomes.
I know it's not a dense numerical treatment, it's a short publication. But I don't see logical failure in extrapolating from past 'rapid' known changes, to adding the current 'rapid' change on top of the last natural one.
[Its *not* a short publication - its quite a long one. There is plenty of room for numbers. Stop making excuses for Hansen! -W]
Hansen is quite duplicitous in the paper when it comes to what he means by "rapid". He titles the final section of the paper "Planet Earth today: imminent peril", which very few people would interpret as meaning the peril is more than a century away, but then goes on to say:
It is difï¬cult to predict time of collapse [of the ice sheets] in such a nonlinear problem, but we ï¬nd no evidence of millennial lags between forcing and ice sheet response in palaeoclimate data. An ice sheet response time of centuries seems probable, and we cannot rule out large changes on decadal time-scales once wide-scale surface melt is underway.
IE, he find no evidence of millennial lags. But if you read the rest of the paper he gives no evidence for less-than-millennial lags either. However, even if we give him "centuries" instead of a millennium lag, one can assume he means at least 2 or 3 centuries. Hardly what I would call "imminent peril".
But when you're using AGW alarmism to push your own anti-growth, nature-over-humanity political agenda, "imminent peril" has a lot more impact than "better keep an eye on those ice sheets in a couple of centuries time".
Once again, one is led to ponder: if this is the best the thought leaders of climatology can produce, isn't high scepticism the only rational response to the current hysteria surrounding global warming?
Last post on this for a while, I promise.
Just agreeing that the wildcard is the big question.
Much discussion going on:
From the second of that group, melting at the past maximum did change these glaciers
"AB: Swath bathymetry records from the onset areas of two paleo-ice streams, the Pine Island and Marguerite ice streams .... these drainage systems were active at the end of the Last Glacial Maximum..."
Honest, William, I'm not 'making excuses' -- you're pointing to what you say are real holes in the paper. Whoever refereed the piece should have pointed them out too.
I ask because I do see more alarming values of 'rapid' are raised in other papers; for example here:
The great ice sheets covering Antarctica and Greenland were, traditionally, believed to take thousands of years to respond to external forcing. Recent observations suggest, however, that major changes in the dynamics of parts of the ice sheets are taking place over timescales of years. These changes were not predicted by numerical models, and the underlying cause(s) remains uncertain. It has been suggested that regional oceanic and/or atmospheric warming are responsible but separating the influence and importance of these two forcings has not been possible. In most cases, the role of atmospheric versus oceanic control remains uncertain. Here, we review the observations of rapid change and discuss the possible mechanisms, in the light of advances in numerical modelling and our understanding of the processes that may be responsible.
But - you're one of the experts. I'm just reading abstracts and asking, why are these people raising these concerns?
I realize this could just be that the International Polar Year is causing a great number of publications, too!
What would suffice -- a table of albedo related to surface area and time of melting, giving heat absorbed? Something known about how surface meltwater can either penetrate, refreeze and crack ice, or reach the base?
[Why are people raising concerns? Because if they weren't oyu wouldn't have heard of them. In this case, the changes are "rapid" is reasonable terms but they apply to small parts of the ice sheets - you'll notice they don't quantify what area is involved -W]
> Here, we review the observations of rapid change
(that's the abstract, all I can see)
> you'll notice they don't quantify what area is involved -W]
In the abstract, no. My point exactly, I can't see all the background info, nor know what's considered well known.
But you're reading the full article, and they still don't quantify the area? I know I've seen other articles mapping melt areas, and could dig them up.
But I can't see as much as you can.
When you say there's no support for these papers, I can only rely on your having made that judgment.
Thanks for keeping us up to date on what's known and not known in the field.
Hank, read this. FTA:
The global warming doomsayers claim the Greenland and Antarctic ice sheets are melting catastrophically, and will cause a sudden rise in sea level of five or more meters. This ignores the mechanism of glacier flow, which is by creep. Glaciers are not melting from the surface down, nor are they sliding down an inclined plane lubricated by meltwater. The existence of ice over three kilometers thick, preserving details of past snowfall and atmospheres used to decipher past temperature and carbon dioxide levels, shows that the ice sheets have accumulated for hundreds of thousands of years without melting. Variations in melting around the edges of ice sheets are no indication that they are collapsing. Indeed "collapse" is impossible.
Hansen is completely wrong. Yet he manages to publish his ravings in Philosophical Transactions of the Royal Society. But of course there's no closed-loop, self-reinforcing academic circle-jerk going on in climatology. What an outrageous suggestion...
Mugwump, you may have mistyped your post: it should read -
But of course there's no closed-loop, self-reinforcing political circle-jerk going on in wingnut web sites. What an outrageous suggestion...
There, fixed that for you.
mugwump: the fact that GIS has been stable for hundreds of thousands of years should not be taken as proof of its stability to the untested climate regime that it will soon enter. Hansen's claims should be examined by careful science. Clearly his assertions need to be filled out with detailed theory/data. Only in that way can they be properly evaluated.
[Just for clarity, let me say that I'm fairly sure that, under BAU, we will be committed, by the end of this century at latest and likely much earlier, to melting Greenland. What I'm not convinced of is that the melt itself this will happen "rapidly". The commitment will be rapid, but not the result -W]
Gareth, how rude of you to refer to our host in such intemperate tones. William has never struck me as a wingnut.
Just for clarity, let me say that I'm fairly sure that, under BAU, we will be committed, by the end of this century at latest and likely much earlier, to melting Greenland.
The problem with BAU is that it never lasts. I wouldn't bet against our ability to produce CO2 sequestering microorganisms by the end of this century or the next that we'll be able to safely release into the atmosphere and have fall as soot after their job is done.
Hansen's claims should be examined by careful science.
No, Hansen should support his claims with some careful science. Otherwise, why should I take his wacko theories any more seriously than anyone else's?
Mugwump, you link to SAPP. See Sourcewatch on them. They're a trade group with an agenda, and not a science site.
Hank, the article is coherent, regardless of the forum. The author seems well-credentialed: Cliff D. Ollier.
Mugwump, AFAICT Ollier is another bitter geology emeritus (there seems to be a tradition) and has no particular qualifications in glaciology. Also, a quick read of his material locates a few scientific errors, and if I can spot 'em they're pretty gross. Why don't you give it a try?
William, you wrote:
As I see it, we either adopt [Hank's] reading of "rapid" - take it within the context of the ice age timescale, in which case its a few thousand years - in which case "rapid" climate change is nothing to worry about at all. Or, we read it to mean "less than a century", in which case we should worry, but in that case the palaeo stuff says nothing useful -W, inline to November 24, 2007 12:24 PM
Do you mean to say that it couldn't be something between several thousand years and less than a century...
I would take a slightly different view.
His idea of near-synchronous is something less than a thousand years which may be less than a hundred years but which is more likely several hundred. That would be near-synchronous in geologic time for the simple reason that we do not have and may never have that kind of resolution.
Now it may very well be the case that the IPCC thinks no further than a century from now -- and it defines the standards by which it judges our actions more or less strictly in terms of their effects within this century. That may be the limits of most people's concerns. In fact, I suspect that for the large majority of humanity the range of their concerns extends beyond a handful of decades.
But Hansen is somewhat different. For him 100,000 years is for all intents and purposes an eternity. But what we commit ourselves to will largely be determined by what we do in this century. And at some level I get the sense that the people who will live with the results of our actions over the course of the next few centuries are almost as real to him as the people who are alive today. He believes that we have an ethical obligation to them.
And as he states,
We argue that the required persistence for this trigger mechanism is at most a century, probably less. Global warming necessarily accompanies ice sheet loss and decreased surface albedo. Global warming, based on both palaeoclimate data and carbon cycle models, is accompanied by increased GHGs. The result is large global warming at terminations.
Climate change and trace gases
James Hansen, et al.
Phil. Trans. R. Soc. A (2007) 365, 1925-1954
Now perhaps the most troubling statement that you discovered in that piece (that is, aside perhaps from a statement expressing the assumption that he was writing to an audience on the other side of the pond) was the following:
We find it implausible that BAU scenarios, with climate forcing and global warming exceeding those of the Pliocene, would permit a West Antarctic ice sheet of present size to survive even for a century.
ibid, pg. 1950, referenced in Thaas outrageous, big Mammy
I believe there was a certain subtlety to it. I take this to be an oblique reference to the IPCC's conservative projection that WAIS will react in a linear fashion over the course of this century.
He specifically criticizes them for this assumption:
Despite these early warnings about likely future nonlinear rapid response, IPCC continues, at least implicitly, to assume a linear response to BAU forcings. Yet BAU forcings exceed by far any forcings in recent palaeoclimate history.
ibid., pg 1936
But he finds it much more plausible that we will see the sea level rise by several meters due to the discharge from both GIS and WAIS under BAU by the end of this century -- and this includes the potential for positive feedback between GIS and WAIS. He suggests elsewhere that 5 m seems much more realistic than 50 cm. And given the fact that we know the process must become non-linear and the fact that the discharge from GIS has doubled and the icequakes (which have a characteristic scale) have tripled within a decade's time, the doubling per decade from which he derived 5 m on the surface at least seems reasonable -- although I doubt he who wish to lay a bet that we will actually see 5 m.
As I see it, that particular "problematic" sentence regarding "implausibility" is simply an oblique reference to the linearity of the IPCC's expectations for the response of the icesheets -- and to the non-linearity of the response that we have seen so far and have good reason to expect. And in human terms, the difference between the IPCC's projections and the behavior from the icesheets which we have reason to expect is of considerable significance to humanity even within the context of this century alone.
Now I do believe that he has some difficulty establishing the context of his concerns: are we talking about this century or the next few centuries? However, I believe that he is also drawing our attention to the fact that of the concerns which, given our linear, conservative estimates, would seem to be several centuries off, many of them may be far closer than we think. As such, a distinction between what concerns us in this century and those in the next couple centuries may at this point be more a source of confusion than clarity.
At the same time, I believe that the boundary between science and advocacy is considerably thinner in his work than is customary, and I myself find some discomfort in it.
[I too think we have a moral obligation to our descendants. So does Exxon. The arguement is about how we act on that obligation. I am very uncomfortable with projecting forward more than a century - that seems to be about the limit of what people think is plausible (and of course many think even that too much).
Hansen says lots of things - you quote, for example, "He suggests elsewhere that 5 m seems much more realistic than 50 cm" and thats typical - that represent nothing more than his personal opinion. They aren't supported by his science. They have no place in a scientific paper, as you r last para suggests -W]
"OK, then in that case we can ignore all his concerns about "rapid" climate change and "imminent" peril, because we have a thousnd years to prepare -W"
And you just know that we'll wait for 990 years before we start. ;)
Steve Bloom, AFAICT Hansen has no particular qualifications in glaciology, Ollier at least speaks sensible physics. But don't be coy, what are his errors in that article?
Here's the problem Hansen faces, as I see it: he wants to parlay an ancient rapid (6m/century) sea-level rise into an imminent threat, based on a positive-feedback albedo argument. You can imagine such a scenario at the end of an ice age when there's an ice-sheet stretching halfway to the equator, because then the derivative of the Earth's albedo as a function of temperature will be much greater. But today we're already in a situation where the ice sheets have retreated to the coldest, most stable locations. Even with "unprecedented" global warming, arguing by analogy with some ancient, half-frozen state is not convincing. He has to show a mechanism.
[Update: there is some weirdness here about someone daring to reject Hansen for being 30 years out of date. But Phil Trans are not so bold -W]
Wow, following that link, Hansen really sounds up himself.
I had a few papers rejected in my time, and while I may privately have ranted about it to my colleagues, I would never have sent out an email like Hansen's. In hindsight, every one of my rejections was appropriate; they spurred me to write a better paper which was subsequently published.
Some points which may clarify arguments:
2. We should differentiate between rapid change by defining rapid as faster than the system can deal with excess CO2, e.g. something like 500 years.
[We should most definitely clearly define our terms before using them, because otherwise people are going to misinterpret them. If we are talking about 21C climate change, then I don't like that defn of rapid; but had Hansen at least defined his terms there would be more clarity. This is a fairly basic idea of science, indeed part of what distinguishes it from non-science (cue quote of Feynman cargo-cult lecture) and Hansen is on the way to putting himself on the wrong side of the line -W]
3. We should differentiate between change and commitment to that change, the "tipping point" beyond which a particular change is inevitable.
[Again, agree -W]
4. Hansen may not be a glacier expert but he is a sea level rise expert, having contributed to that area very early on (see for example Jim Titus' web page for comments on this, Titus is the EPA expert on sea level rise and its consequences).
[I'm not sure what you mean by that, in the sense of what I'm supposed to take from it. He's an expert - I should trust his personal opinions? Perhaps, but even if so he should publish them as such and in a suitable venue. But I'd rather not trust him - I'd rather read the arguments he puts forward to justify his viewpoint -W]
Some points which may clarify arguments:
We should differentiate between rapid change by defining rapid as faster than the system can deal with excess CO2, e.g. something like 500 years...
And "imminent peril"? Also 500 years?
I'll take my chances.
> defining rapid as faster than the system can deal
> with excess CO2
That's how I read it. I'd thought the usage obvious (obviously it wasn't!). Most of humanity's effect on ecology is 'rapid' in the same sense, too fast for natural cycling of whatever length. To me it seems a natural measure of time and effect.
Thanks Eli, clearly put.
> differentiate between change and commitment to change
This is where 'rapid' confused people I think. Is it a rapid change if we don't see any effect but we're certain our grandchildren will? It's a new perspective no society has had til science allowed it. 3 percent a year is imperceptible over human generation lengths without history or science.
> I'd rather read the arguments he puts forward to
> justify his viewpoint -W
What if you tried taking 'the other side' (pardon the linear ity, Tamino!) of the argument, William? If you were to, as an exercise, look at what you know is published and what you're aware of that hasn't been published in your field, could you find a basis for this concern?
[As far as I know, there is nothing concrete published to suggest high (> 2m, say) sea level rise within a century. There are plenty of "we might worry about..." papers.
I think the focus here is all wrong. The evidence suggesting that +2 oC would be dangerous from an ecological POV within a century is far stronger -W]
William (inset to November 26, 2007 1:58 AM) wrote:
I too think we have a moral obligation to our descendants. So does Exxon. The arguement is about how we act on that obligation. I am very uncomfortable with projecting forward more than a century - that seems to be about the limit of what people think is plausible (and of course many think even that too much).
I am not so sure about Exxon. Frankly that is an enigma. As for how far one projects, I would think that the paleoclimate record lends a certain plausibility to what we can expect in the future.
William (inset to November 26, 2007 1:58 AM) wrote:
Hansen says lots of things - you quote, for example, "He suggests elsewhere that 5 m seems much more realistic than 50 cm" and thats typical - that represent nothing more than his personal opinion. They aren't supported by his science. They have no place in a scientific paper, as your last para suggests -W
I would think that the 5 m is at least plausible, given what we see in the paleoclimate record (both in terms of the apparent rate of 5 m and the long-term climate sensitivity which is suggested by the paleoclimate record of Antarctica), the doubling that we have seen in the rate of discharge in Greenland, and the fact that exponential behavior is typical of chaotic systems.
Admittedly, this is a weak argument, but it would seem stronger than the IPCC's linear projection. Likewise, I think that the scientific community could do a better job of explaining the potential risks.
[Its an enormously weak argument. A better way of putting it would be that the palaeo record doesn't forbid it. What you're demonstrating, I think, is that whatever Hansen is arguing is unclear and vague.
What do you mean, IPCCs linear projection?
The sci comm is doing its best. We don't know what the risks are and we can't quantify them any better than they have been. Thats no excuse for making wild-eyed guesses -W]
But Stefan Rahmstorf's projection for sea level has more raw empirical support for the time being. And I understand that we are now beginning to model the behavior of icesheets -- and as this modeling develops, it will no doubt do a better job than either of the three projections.
[People have been modelling ice sheets for ages -W]
At the same time, given the present state of our knowledge, I wouldn't simply dismiss his arguments as being entirely without merit. However, I realize that my own views in this matter carry very little weight. I simply haven't the background.
[I would come very close to dismissing his arguments as being without merit. Though of course, he could be right about the outcome - thats another matter -W]
William (inset to November 26, 2007 11:40 AM) wrote:
What do you mean, IPCCs linear projection?
Of the response to BAU forcings.
William (inset to November 26, 2007 11:40 AM) wrote:
he could be right about the outcome - thats another matter.
I will leave "He could be right about the outcome" as a defense for the denialists to appeal to. Not my bag.
Anyway, I appreciate your patience.
Mugwump, you didn't spot the errors? Interesting. Just as a teaser, you might want to have a close look at his claims about suitability of locations for taking ice cores and about the importance of geothermal melting. You say you're a scientist, but if so not only have you obviously made no effort to familiarize yourself with the climate science literature, you're perfectly happy to serve up non-peer reviewed articles by people with no relevent qualifications.
Regarding Hansen, had you read some of his prior material you would know that the reason for his present focus on the ice sheets is because leading glaciologists have been telling him things privately that they're not willing to repeat in public or in the literature. As well, people who have been working on GCMs for as long as Hansen have to know a fair amount about the science underlying the models, and that certainly includes the ice sheets.
People like William might be happier if Hansen were to behave with the reticence more normally associated with senior scientists. I assume he must be thinking of David Vaughan in particular as a suitable role model.
Oh go on Steve, stop teasing - just tell us where the errors are.
Regarding Hansen, had you read some of his prior material you would know that the reason for his present focus on the ice sheets is because leading glaciologists have been telling him things privately that they're not willing to repeat in public or in the literature.
Ummmm, rrriiiight. I'm starting to spot a trend. Have you seen "A beautiful mind" Steve?
mugwump (November 26, 2007 7:08 PM) wrote:
Ummmm, rrriiiight. I'm starting to spot a trend. Have you seen "A beautiful mind" Steve?
You seem familiar...
Did I ever run into you over at Pharyngula? You remind me of someone there. In fact, you remind me of a good number of someones there.
Did I ever run into you over at Pharyngula?
Never had the pleasure.
> [not] Pharyngula
Google tangential freebie:
> leading glaciologists have been telling him things
> privately that they're not willing to repeat in public
> or in the literature.
This is the worry
mugwump, I have no interest at all in playing whack-a-mole with people who won't lift a finger to defend claims made by a non-expert source they cited. Those hints were quite broad, BTW, but of course you wouldn't know that if you're not familiar with the material. You could try finding a glaciologist or ice sheet modeler who makes similar claims, in which case I probably could be provoked into affirmatively addressing them. Good luck with that.
I didn't see "A Beautiful Mind," but I assume you're implying that Hansen is fantasizing. Were it not for the public complaints from senior glaciologists about being leaned on, that could possibly be more than a made-up talking point. You might consider that Hansen didn't get to be the (your words) "designated leader of climatology" by trailing the field. He got there by being out in front of the field and by, let's not forget, being right.
Speaking of which, I see in today's The Hindu that Hansen's efforts are starting to bear fruit.
Antarctic ice sheet collapse is mentioned in the article on the front page of this week's EOS (I typed in a bit of an excerpt in a thread over at Tamino's, here:
But we'd been over the EOS article's main cite, last July, in another discussion about Hansen's writing:
No news here, move along.
[Errrm yes, the EOS article is suitably vague -W]
mugwump, I have no interest at all in playing whack-a-mole with people who won't lift a finger to defend claims made by a non-expert source they cited.
Que? You've consistently refused to state the prosecution's case; how am I supposed to defend against it?
Well, come January, supposedly, my $20 to the AGU will get me full text of articles for a year, not just abstracts, and I can actually read some of this stuff for myself instead of relying on the kindness of others.
This is the cite for the EOS article, and a bit from the earlier Globalchange post:
"... Our principal results are that (1) marine ice sheets do not exhibit neutral equilibrium but have well-defined, discrete equilibrium profiles; (2) steady grounding lines cannot be stable on reverse bed slopes; and (3) marine ice sheets with overdeepened beds can undergo hysteresis under variations in sea level, accumulation rate, basal slipperiness, and ice viscosity...."
[These are theoretical results, but everyone knew this anyway. What is needed are timescales; these are completely absent, because of the nature of the study -W]
I see NASA and BAS have just come out with a highly detailed atlas of the surface of Antarctica (the website for it is down from too much attention already). Will they also have maps of the radar imagery of the seabed showing the base of the ice? I recall earlier images that showed very precise sharp clear drainage patterns toward the middle of Antarctica, and as each led toward the edge the image became smoother and apparently was showing a mass of mud and silt all pushed out to the edge of the basin making the high rim around the deep center everyone keeps mentioning, the 'reverse' slope. It's also interesting to wonder how that ring of silt will behave if the ice behind it changes.
Anyone know if there's a steady outflow of meltwater from under the ice, flushing the channels out and keeping the water fresh (and presumably keeping the biota that prefer full ocean salinity out to the edges)? Or have the drills that reached water below the ice found whether it's salt?
Hank, I would be surprised if there were radar imaging. As I remember the armed forces of the world have strongly resisted such precision mapping being available in public, which has lead to the strange situation that the metrology of Mars is probably better determined than that of the Earth.
"I see NASA and BAS have just come out with a highly detailed atlas of the surface of Antarctica (the website for it is down from too much attention already)."
There's some talk that it could be made available to Google Earth.
Eli, there are some, Google
antarctic ice penetrating radar
I'll poke around, but can't right at the moment
Not the one I recall, I'll keep looking. Lots more articles, just haven't found the images.
I had a brief conversation with Ian Howat (ice sheet specialist just completing his post-doc at UWash/NSIDC) a couple of months ago. He told me that he thought the existing models were up to simulating Greenland ice sheet behavior, and that the problem was indeed a lack of the radar maps. He also said that the mapping has been started in Greenland. I pointed out to him that Michael Oppenheimer had said in an RC guest editorial about a year ago that it would be on the order of five years before good model results could be had, but Ian thought it would be much sooner (for Greenland, anyway).
Another press release from ANDRILL:
A second season in Antarctica for the Antarctic Geological Drilling Program has exceeded all expectations, according to the co-chief scientists of the program's Southern McMurdo Sound Project.
And, supporting Eli's point, we do indeed have radar capable of mapping the subsurface, even through later lava flows -- on Mars.
I'd bet, from this, that military satellites have got a whole lot they're not revealing, on subsurface Earth structure.
Time for another Gore Box for declassification of polar military archives, I think -- South Polar, this time, like he got done as when he was a Senator to declassify a lot of the Navy's secret Arctic data.
Look what they can do through lava flows, and with dinky little civilian-grade equipment:
I've been wondering what might be known but classified, particularly since Wegman, long associated with military scientific work, said at those Congressional hearings that it was time to put aside the 'hockey' nonsense and that he was worried about the oceans. I wondered why, and never found another word about his concern. It seemed a hint at the time.
Hank, are you sure that "$20 to the AGU will get me full text of articles for a year". I got the impression that a subscription would be needed to each of the journals. Why else would there be less expensive electronic subscriptions?
Bloom, obviously there can be stress levels which result in plastic flow without "geothermal melting". But, Ollier's brief mention hardly amounts to an overemphasis on its importance. Of course any geothermal increment in temperature would lower the stress threshold for plastic flow, and the extent of its presence would determine the level at which the transition occurs.
Martin, I'm never sure with AGU, their promotional email urging me to renew touted an introductory offer on their new digital library, saying AGU membership for 2008, its first year, would allow access to articles, with some delay ("embargo") after publication. But, sigh, I think you're right, it seems they meant "access if you pay full price" -- they're too smart for me, I'm just an amateur reader.
Back on Hansen, I find three scenarios here, the third of which considers catastrophic collapse of the ice caps in this century and a 2-meter sea level rise, interesting because from a very blue-ribbon panel, and it comments explicitly on climatologists having difficulty going beyond what they're sure they know to address catastrophic possibilities. It's a very large PDF:
Hank, I genuflect in your general direction. That is a most interesting document, for all sorts of reasons, many of them having nothing to do with science...
Meant to add a taster of the content (from the exec summary, describing the worst case scenario they use):
As one participant noted, "unchecked climate change equals the
world depicted by Mad Max, only hotter, with no beaches, and perhaps with even more chaos."
I've been noticing for some years now that when I go searching for climate information, if I throw in +"U.S. Navy" or +"Navy Postgrad" the results always have more interesting and varied material that I wouldn't have found otherwise. And search engines like DTIC get even more stuff that's available but not much if ever reported on. No surprise, I guess. It's public but they don't have a PR department touting the work.
And sometimes, sites that froze in time somehow: