Sunday, April 01, 2007

Ethon brings word of April Fool's Jokes Boulder style

It's pretty hard to keep the irony meter on scale these days. The National Anonymice Academy had no sooner taken up the issue of ice cap rot, when Steve Bloom scurried in from Austin Texas, with news from the parallel meeting of the Western Antarctic Links to Sea Level Estimation (WALSE) Workshop. This proves the power of convening a meeting of the Anonymice Academy for focusing attention on important matters. Word had also run to our friends in Boulder who, if they were the long eared types would be complimented on the wonderful knots they are tying in their ears.

Eli thought it would be a good thing to contrast and compare some of the text from the Hansen Arxiv paper the Academy has been studying, with the consensus statement that emerged from the WALSE group, who presumably had a number of expert glaciologists sitting in.

  • Satellite observations show that both the grounded ice sheet and the floating ice shelves of the Amundsen Sea Embayment have thinned over the last decades.
Hansen: The most compelling data for the net change of ice sheets is provided by the gravity satellite mission GRACE, which shows that both Greenland (Chen et al 2006) and Antarctica (Velicogna et al 2006) are losing mass at substantial rates. The most recent analyses of the satellite data (S. Klosco et al priv. comm.) confirm that Greenland and Antarctica are each losing mass at a rate of about 150 cubic kilometers per year, with the Antarctic mass loss primarily in West Antarctica. These rates of mass loss are at least a doubling of rates of several years earlier, and only a decade earlier these ice sheets were much closer to mass balance (Casenave 2006)....

Warming ocean waters are now thinning some West Antarctic ice shelves by several meters per year (Payne et al 2004; Shepherd et al 2004).
  • Ongoing thinning in the grounded ice sheet is already contributing to sea-level rise.
Hansen: Under BAU forcing in the 21st century, sea level rise undoubtedly will be dominated by a third term (3) ice sheet disintegration. This third term was small until the past few years, but it is has at least doubled in the past decade and is now close to 1 mm/year, based on gravity satellite measurements discussed above.
  • The thinning of the ice has occurred because melting beneath the ice shelves has increased, reducing the friction holding back the grounded ice sheet and causing faster flow.
Hansen: Acceleration of ice sheet disintegration requires tapping into ocean heat, which occurs primarily in two ways (Hansen 2005): (1) increased velocity of outlet glaciers (flowing in rock-walled channels) ice streams (bordered mainly by slower moving ice), and thus increased flux and subsequent melting of icebergs discharged to the open ocean, and (2) direct contact of ocean and ice sheet (underneath and against fringing ice shelves). Ice loss from the second process has a positive feedback on the first process: as buttressing ice shelves melt, ice stream velocity increases.
  • Oceanic changes have caused the increased ice-shelf melting. The observed average warming of the global ocean has not yet notably affected the waters reaching the base of the ice shelves. However, recent changes in winds around Antarctica caused by human influence and/or natural variability may be changing ocean currents, moving warmer waters under the ice shelves.
Hansen: Modeling studies yield increased ocean heat uptake around West Antarctica and Greenland due to increasing human-made greenhouse gases (Hansen et al 2006b). Observations show a warming ocean around West Antarctica (Shepherd et al 2004), ice shelves thinning several meters per year (Rignot and Jacobs 2002; Payne et al 2004), and increased iceberg discharge (Thomas et al 2004).
  • Our understanding of ice-sheet flow suggests the possibility that too much melting beneath ice shelves will lead to “runaway” thinning of the grounded ice sheet. Current understanding is too limited to know whether, when, or how rapidly this might happen, but discussions at the meeting included the possibility of several feet of sea-level rise over a few centuries from changes in this region.
Hansen: Positive feedback from loss of buttressing ice shelves is relevant to some Greenland ice streams, but the West Antarctic ice sheet, which rests on bedrock well below sea level (Thomas et al 2004), will be affected much more. Loss of ice shelves provides exit routes with reduced resistance for ice from further inland, as suggested by Mercer (1978) and earlier by Hughes (1972). ...

An important point is that the non-linear response could easily run out of control, because of
positive feedbacks and system inertias.......The nonlinearity of the ice sheet problem makes it impossible to accurately predict sea level change on a specific date.

We leave it as a challenge to find Hansen's opinion on the remaining issues. A good place to start is his slippery slope argument in Climate Change, which, among other things points to problems with ice sheet models.
  • The experts agreed that to reduce the very large uncertainties concerning the behavior of the Antarctic ice in the Amundsen Sea Embayment will require new satellite, ground, and ship-based observations coupled to improved models of the ice-ocean-atmosphere system. Issues include:
  1. The recent changes were discovered by satellite observations; however, continued monitoring of some of these changes is not possible because of a loss of capability in current and funded satellite missions.
  2. The remoteness of this part of Antarctica from existing stations continues to limit the availability of ground observations essential to predicting the future of the ice sheet.
  3. No oceanographic observations exist beneath the ice shelves, and other oceanographic sampling is too infrequent and sparse to constrain critical processes.
  4. Current continental-scale ice sheet models are inadequate for predicting future sea level rise because they omit important physical processes.
  5. Current global climate models do not provide information essential for predicting ice sheet and oceanic changes in the Amundsen Sea Embayment; for example, ice shelves are not included.
However, Eli would appreciate some furry rodent to explain the contradiction that lunch claims in his April Fools joke:

2. There is the "possibility of several feet of sea-level rise over a few centuries from changes in this region." This contrasts strongly with Jim Hansen's assertion that

"Spatial and temporal fluctuations are normal, short-term expectations for Greenland glaciers are different from long-term expectations for West Antarctica. Integration via the gravity satellite measurements puts individual glacier fluctuations in proper perspective. The broader picture gives strong indication that ice sheets will, and are already beginning to, respond in a nonlinear fashion to global warming.There is enough information now, in my opinion, to make it a near certainty that IPCC BAU climate forcing scenarios would lead to disastrous multi-meter sea level rise on the century time scale"
unless someone out there thinks that several feet is substantially different from multi-meter or that a large sea level rise over 1-3 centuries would be a walk in the park. Living a mile or so up may give one a sense of security we at sea level lack. OTOH, there is less O2 up high.

16 comments:

Adam said...

I dunno but I always thought that "several" meant "more than three" (which is a "few").

I also think "a few centuries" maps to a "century timescale" quite well.

But maybe it's just a value judgement that obvioulsy, no scientist is allowed to make.

Anonymous said...

From the statement:
"The recent changes were discovered by satellite observations; however, continued monitoring of some of these changes is not possible because of a loss of capability in current and funded satellite missions."


"No oceanographic observations exist beneath the ice shelves, and other oceanographic sampling is too infrequent and sparse to constrain critical processes."

This is a glaring omission. Remote sensing from above (satellites) and from the surface (eg, visible inspection and seismic surveying) can only get you so far -- although both the latter should be a mandatory component of future monitoring (ie, they should be fully funded).

If we had a President interested in science in general -- and not actually hostile to climate science in particular -- perhaps he/she would have had one of the Navy's smaller submarines doing recon work near the ice shelves by now.

Instead, we have a guy who has actually allowed cuts in funding of programs to send up new satellites to monitor things like ice sheets.

Anonymous said...

Roger Pielke posted on his blog: "In a paper by Jim Hansen that we discussed last week, he called for a consensus statement to be issued on global warming, West Antarctica and sea level rise, from relevant scientific experts. A group of scientists have beat him to the punch issuing a consensus statement last week"

Well, actually, no.

First, it obviously never occurred to RP that Hansen's speaking/writing on the subject of sea level rise for some time now (not just in the "Reticence" paper) and his correspondence with scientists studying ice sheets (at NASA and elsewhere) may just have been one of the impetuses for the recent meeting.

Second, Hansen called for a National Academy study as the best case scenario -- a little different (just slightly) from the brief meeting and statement that was just issued.

It shows a poor understanding on Pielke's part that he (apparently) sees the two as interchangeable.

Anonymous said...

It is instructive to ask where the "several feet" prediction might come from.

It almost certainly comes from an assumption of a "linear" approximation with regard to ice sheet melting.

Hansen points out the contradiction involved in assuming a continuation of the "linear" approximation:

"this approach cannot be taken as a realistic
way of projecting likely sea level rise under BAU forcing. "The linear approximation fits the past sea level
change well for the past century only because the two terms contributing significantly to sea level rise
were (1) thermal expansion of ocean water and (2) melting of alpine glaciers."

"Under BAU forcing in the 21st century, sea level rise undoubtedly will be dominated by a third
term (3) ice sheet disintegration. This third term was small until the past few years, but it is has at least
doubled in the past decade and is now close to 1 mm/year, based on gravity satellite measurements
discussed above. As a quantitative example, let us say that the ice sheet contribution is 1 cm for the
decade 2005-2015 and that it doubles each decade until the West Antarctic ice sheet is largely depleted.
That time constant yields sea level rise of the order of 5 m this century. Of course I can not prove that my
choice of a 10 year doubling time for non-linear response is accurate, but I am confident that it provides a
far better estimate than a linear response for the ice sheet component of sea level rise.
An important point is that the non-linear response could easily run out of control, because of
positive feedbacks and system inertias."

Anonymous said...

Republican favorite, Roger Pielke Jr., is so baffling that it's hard to even make a joke out of him. He's always contradicting himself while at the same time referencing himself to provide support to his own arguments.

A couple of things.

1. It's of course hilarious that Roger seems pleased that some scientists are getting together for a consensus statement, since he always argues against consensus. The obvious reason for this, seems to be that Roger is happy to find any way, no matter how minor, to pull the rug out from beneath Hansen, who is a favorite target of Roger's.

2. This consensus statement comes out from these scientists, and the first thing that Roger does is find "considerable uncertainties" in the statement. In actuality, it's pretty much a string of simple declarative statements, and I can't find the word "uncertainty" anywhere in the passages Roger highlights.

Does Roger even bother to listen to others, or does he just wait for a brief lull in the convesation to start babbling?

Anonymous said...

RP is always good for a few laughs:

First, he says that the "take home point [from the ice scientists' statement] is that there remain substantial uncertainties" with regard to how much ice sheet melting/breakup will contribute to sea level rise.

Then he immediately goes on to say that sea level rises much beyond the IPCC estimate are "low probability" events.


"Bottom line: Sea level rose about 20 cm over the past century. The IPCC expects that it may rise from less than that amount to about 60 cm over the next century. RealClimate says they see another 40 cm possible in the IPCC report. And there is a long thin probability tail of higher amounts with low probability and high consequences." (RP)

I hate to break to Pielke but "uncertainty" with regard to how much ice sheet melt dynamics will contribute to sea level rise does not translate to "we're almost sure it won't contribute much".

That's a good one, but Pielke saves the best for last:

"Who will eventually be proven correct? I have no idea. Nor do I think that it matters at all from the perspective of policy"

I'm sure most actuaries would be rolling on the floor after reading that one. ("No, it makes no difference from our business policy standpoint whether sea level rises a few feet or a few meters")

Let's assume for kicks that Pielke is correct to assume that sea level rise > 1 meter has "very low probability" of occurring (corresponding to the "long thin probability tail", as he put it) .

From that, I'd have to say that we must conclude that Pielke has probably never heard of the idea of "expected cost" as it applies to insurance risk analysis.

As the insurance industry knows all too well, it is precisely those "low probability-high consequences" events (Hurricane Katrina, anyone?) that can put you out of business.

Anonymous said...

Where's John Fleck? (sounds like a kid's book, no?)

Someone should really inform him of a Pielke Piling (defined as "more than two statements in a row on a blog criticizing RP"), since he so enjoys disputing the right of anonymice to criticize (even if not the validity of the criticisms themselves).

But just let it be known...


"We hold these truths to be self-evident, that all anonymice are created equal, that they are endowed by their (Furry) Creator with certain unalienable Rights, that among these are Life, Liberty and the Criticism of Roger Pielke/Pursuit of happiness..."

Adam said...

I think these two comments on RC are useful (I'm sure most on here have seen them).

"One of the reasons this stuff wasn't included in detail in the IPCC report is that it is all pretty new. Anythinig included in the report has to have stood the test of time, at least a bit. The rule was anything cited had to be in press by May 2006. Many of the important papers postdate that. All this goes to show that IPCC is for the most part, conservative. That's how science works, contrary to what the "skeptics" claim.--eric"

http://www.realclimate.org/index.php/archives/2007/03/the-ipcc-sea-level-numbers/#comment-29651

"I did not know Hansen's paper but read it just now. I fully agree with what he writes about "scientific reticence", his words echo my own experience very well. In many IPCC discussions I have noticed a strange asymmetry: people were very concerned about possibly erring on the high side (e.g., the upper bound of sea level rise possibly being criticised as "alarmist"), and not very concerned about erring on the low side (or some even regarding this as a virtue of being "cautious")....stefan"

http://www.realclimate.org/index.php/archives/2007/03/the-ipcc-sea-level-numbers/#comment-29719

Especially as Stefan took part in IPCC discussions and both quotes are in an article where Stefan states that he could not rule out a rise exceeding one metre (this century). This is independent of Hansen as he had not read his paper.

Anonymous said...

Thanks adam.

I think that was Hansen's main point about the IPCC report as well -- that it is conservative by its very nature and that it is essentially outdated when it goes to press (or even before).

Actually, I think there are two reasons for the conservatism:

1) Scientists are a conservative lot.

2) IPCC has been burned in the past simply for including a range of scenarios (some of them less likely but more costly/dangerous). I think they did not want their main message to get lost in a discussion of uncertainties (as it has in the past)

In that regard, the "strange asymmetry" that Stefan noted makes perfect sense.

Anonymous said...

Hansen assumes non-linear ice sheet disintegration with a doubling time of 10 years and a starting value of 1 cm and comes up with about a 15m sea level rise over the next 100 years (mostly due to ice sheet melting/breakup).

But, for kicks, let's be more conservative and assume sea level rise from melting/disintegrating ice sheets is again non-linear but begins at 1mm/year (current, based on satellite measurements, as Hansen says)

Further assume that this yearly rise doubles every 20 years (as opposed to the ten year doubling Hansen assumed.

In other words, though we have no reason for believing this a priori, assume that the past ten years were "uncharacteristically" warm (ie, higher than they might have been based on the increase over the preceding 30 years) which led to faster disintegration of ice sheets than what might be expected in the future)

Assume total sea level rise due to ice sheet disintegration as a function of time is given by

SLR = (C1/C2) (e^(C2*t) - 1)

C1 = 1mm (starting value for yearly rise)
C2=0.034657 (for 20 year doubling)

That will mean a total sea level rise between now and the end of the century due to ice sheet changes alone of about 700mm (0.7m).

The latest IPCC (central) estimate for sea level rise through 2100 is 48cm. Part of this is attributed to melting of Greenland and Antarctic ice (max of 90mm and 20mm, resp). If one subtracts the max for the latter estimates from the central overall value (just to make sure we are not double counting), one gets 37cm.

If one adds this 37cm to the 70 cm from above, one gets roughly one meter rise by 2100.

So, in other words, the above assumptions already put sea level rise into the (meter/century) category rather than (ft/century) category.

If one runs the experiment with the above numbers (20 year doubling and starting rise of 1mm/yr) over the next two centuries (200yrs), it gives a total sea level rise of almost 30m.

It's not hard to see where Hansen's concern comes from. Even if you make the doubling time 50 years, and you run the experiment over 3 centuries, you get nearly a 5m rise (using the same 1mm per year starting value for the rise)

With a nonlinear response, the result is almost always disconcerting if you go far enough into the future.

If your time frame is just a few centuries, you would have to use a pretty long doubling time and/or a pretty small starting value for the yearly rise in order to keep the overall rise small.

Anonymous said...

Correction for above

I wrote above: " In other words, though we have no reason for believing this a priori, assume that the past ten years were "uncharacteristically" warm (ie, higher than they might have been based on the increase over the preceding 30 years) which led to faster disintegration of ice sheets than what might be expected in the future)"

What I meant to say above was that to be conservative, I assumed that the doubling time is actually more than ten years (to provide for the possibility that the fact that the past few years do not follow the pattern of warming over the past 30 might be due partially to "scatter" (things other than CO2 GHG increase)

Anonymous said...

Incidentally, for those who wonder where the (ballpark) starting value for yearly sea level rise input to the above equation comes from, look at the satellite sea level graph in this
presentation
by NASA scientist Waleed Abdalati
which shows sea level rise over the past 14 years, which averaged about 3.4mm/year.
You can also see a ramping up in the yearly increase (from about 2.7mm/year over the years 1993-2000 to about 4.0mm/year over the last 7 years.

As you can see, the 1mm used above is actually conservative, if the the information in that graph is indicative of a pattern that will continue into the future.

Not only that, the graph also shows the origin of the "nonlinear" sea level rise assumption and (again assuming the pattern persists) even gives you an idea of the doubling time (which is closer to Hansen's 10 years than the 20 I assumed for kicks above).

Of course, it is possible that what has happened over the past 14 years is not indicative of an exponential pattern that will continue as temperatures continue to rise.

But one really has to wonder.

By the way, the author of the above presentation is an expert on ice sheets and glaciers (and one of James Hansen's colleagues at NASA. It lloks to me like the two have been sharing data and ideas!).

Dr. Waleed Abdalati,
the Head of NASA's Cryospheric Sciences Branch, at the Goddard Space Flight Center (GSFC), Greenbelt, Md. conducts research on high-latitude glaciers and ice sheets using satellite and airborne instruments

Anonymous said...

Here's similar information to that contained in the above presentation (about the relationship of ice sheet melting/breakup to sea level rise) from an earlier NASA page

That's what the experts at NASA say, but one really does not have to be an ice expert to see that something is going on with the ice sheets that is out of the ordinary (at least as compared to the "ordinary" over the past 50 years).


“We’ve found that the largest likely factor for sea level rise is changes in the amount of ice that covers Earth. Three-fourths of the planet’s freshwater is stored in glaciers and ice sheets, or about 220 feet of sea level," said Dr. Eric Rignot, Principal Scientist for the Radar Science and Engineering Section at NASA’s Jet Propulsion Laboratory in Pasadena, Calif. Research results by Rignot and partners, published in an October 2004 article in Science Magazine, further offer evidence that ice cover is shrinking much faster than thought, with over half of recent sea level rise [ie, over 1.5mm/year] due to the melting of ice from Greenland, West Antarctica’s Amundsen Sea, and mountain glaciers.



The latest sea level research conducted by Dr. Steve Nerem, Associate Professor, Colorado Center for Astrodynamics Research at the University of Colorado in Boulder, and his colleagues, published in a 2004 issue of Marine Geodesy Journal, has found that recent TOPEX/Poseidon and Jason satellite observations show an average increase in global mean sea level of three millimeters a year from 1993-2005. This rate is more than 50 percent greater than the average rate of the last 50 years.

Anonymous said...

Another Pielke Koan:


According to Pielke, the take home point from the recent meeting of ice scientists was that "there remain substantial uncertainties" with regard to how much ice sheet dynamics will contribute to seal level rise.

Pielke nonetheless places great emphasis on their statement of the
"possibility of several feet of sea-level rise over a few centuries from changes in this region."


Finally, Pielke concludes that "This contrasts strongly with Jim Hansen's [multi-meter sea level rise on century time scale] assertion."

See the logical problem here?

If there are considerable uncertainties in the ice scientists knowledge, then surely their estimate of a rise of "several feet" can not be all that accurate. In fact, if we are to take the two things together: "uncertainty about several feet estimate", we must necessarily allow for the possibility that it might be more than several feet (perhaps even several meters, as Hansen indicated)

Anonymous said...

Pielkean Logic is indeed quite interesting.

Axiom 1:

"Any physical process that can't be described in great detail and/or predicted with great certainty is exceedingly unlikely to occur."


Corollary 1:

"we need not worry about those things about which we are ignorant because they will almost certainly not occur."

Example of Corollary 1 in action:
"we need not worry about how ice sheet dynamics will affect sea level because don't know about ice sheet dynamics".


Corollary 2: "the more ignorant we are about something, the less likely it is to happen."

Example of Corollary 2 in action:

"We should purposely keep ourselves in dark about ice sheet dynamics because that will ensure that nothing bad happens in the future."

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