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Climate Science Ruckus: Hansen, Foraminifera and Paleo-Temperatures

by Nomad Wed Oct 4th, 2006 at 06:06:58 PM EST

I haven't done one of these in a while mostly because I'm shifting my priorities elsewhere, but the below is too exemplary to my own opinion to let it pass by.

The past few days, an insightful series of posts have appeared at Climate Audit which tackle a new PNAS publication by Jim Hansen, a name that should sound pretty familiar by now, being one of NASA's more prolific climate scientists. Hansen's article bears the title "Global Temperature Change" and is available here: http://www.pnas.org/cgi/reprint/0606291103v1.

In the midst of this review, a new comparison is made between modern sea surface temperatures (SST) and data from a proxy for paleotemperatures for the past Holocene (past 13.000 years). This brings Hansen to the following conclusion:

Most of the world and the global mean have warmed much as the [Western Equatorial Pacific] WEP and Indian Oceans. We infer that global temperature today is probably at or near its highest level in the Holocene.

Yet not all is as sound as it appears to be.


We need to start at the beginning: how did Hansen and his team construct this figure?

At the right of the figure, from 1870 to 2005, modern measurement temperatures of the upper layer of the ocean are plotted. This is called the Sea Surface Temperature (SST) . Although there are several techniques to determine the SST, nowadays the most commonly used measurements come from satellite data. Before the satellite age, people used buoys with attached thermometers and, even more simply, pulling a bucket of sea water and sticking a thermometer in it. There's also some wriggle room left how to connect this patchwork of datasets, but let's not go there. The whole of it gives a reasonable reliable record.

At the left of the vertical line, another set of data has been plotted. Although plotted as temperature, they are not direct measurements, but inferred from a proxy. And in this case: the shell of a particular critter of the ocean is used: the foraminifer G. ruber (see picture right). Foraminifera are miracles of evolutionary creativity worthy of its own diary of wonders. They are to this day able to completely frustrate earth scientists and biogeologists. Foraminifera are single celled organism which are capable of forming a calcium carbonate shells (or sometimes even from silica). Without this capacity of locking carbon away into gigantic limestone formations (think: Dover, Brittany) there wouldn't have been ice ages and the world today would've been a lot hotter - but the important bit here is that their shells are used for establishing a paleo-temperature record.

How does that work? Synopsised: People take a core of the ocean's sediment, sample it in tiny bits, filter it for specific foraminifera (which means: picking them by hand), crush the shells and run the powder through a spectrometer to establish the concentration of two elements in particular: Calcium (Ca) and Magnesium (Mg). Magnesium is an element which can substitute for calcium in the calcium carbonate shell but - and this is the clincher - the concentration of magnesium in the shells varies under certain conditions. One of them being: water temperature.

Therefore, if people take a sediment core, sample various ages, determine the Mg/Ca ratio in the specific foraminifera and plot it, then bingo: you've a technique that is indicative of a temperature of that time. Or with the jargon: you have a paleo-thermometer.

Hansen et al took the Mg/Ca data from a sediment core which was taken nearby the SST temperature measurements and then combined the two into one graph, a process which has been coined splicing by those critical of that approach. Because what happens is that two different kinds of datasets are juxtaposed and presumed equal.

And here start the problems with the whole figure: that's still a pretty big presumption, and Hansen's article spends barely a few lines on the diverse and complex difficulties still present with establishing a reliable temperature proxy.

It does great injustice to a whole branch of science in foraminifera proxies by wrapping it up with this discussion: "The paleoclimate SST, based on Mg content of foraminifera shells, provides accuracy to ~1°C." And a few lines more.

Because foraminifera proxies do not equal the SST. The G. rubber foraminifer floats relatively shallow beneath the ocean surface - but it's not at the surface. So a conversion is needed. This is supposed to have been done already - but it's not mentioned. And articles on this topic sprinkle with various confidence intervals, from 0.6 to 1.7°C.

Secondly, a more serious problem which is currently deeply under research in this field arises: the problem of dissolution after formation. Since when foraminifera die, they sink to the bottom of the ocean and stick around there, until they're retrieved years later with the drilled core. But that implies that they've been up to tens of thousands year exposed to different conditions, which can easily affect the Mg/Ca ratio - and hence affects the paleo-temperature negatively. In that case: the stored Mg/Ca ratio will give you a lower paleo-temeperature.

To this date it has not been decided what a correct conversion factor for that effect would be - or whether it is at all possible to get one. But even a modest attempt would increase the paleo-temperature upward. Combine that with the previous conversion needed and you can end up with a graph that looks like this:

Graph from Climate Audit
Black = Original plot from Hansen et al article
Red = Amended calculation using dissolution corrections

What does this say? To me, it says that, as with many proxy studies, you can't say anything useful at all. Hansen et al use an argument which shouldn't be used as one. With fault ranges this big, the argument becomes invalid - for now.

As long as the accuracy of proxies are hampered by their fault ranges, this kind of criticism is hard to shake off. Foraminifera proxies may be a precise tool, but there is still a set of them that suffers up to this day from being inaccurate. That may change, and I rather see it happening sooner rather than later. It is however a faux pas for climate scientists to ignore these pitfalls- it is not justified by the urgency of the climate debate of today. This way, it won't help to convince people - in fact, I've been growing towards the position that it is counter-productive.

Climate Audit has more critical notes to places - about which I can neither corroborate nor disagree with - such as the alignment of the two datasets, the temperature data itself, and some more. Be that as it may, just turning a blind eye to the problems still surrounding the foraminifera proxies does the science no good.

Climate Audit posts on the Hansen et al article:
Hansen Simplified
Hansen and Bracket Fatigue
The Hansen Splice
Barker 2005 - A good overview of foraminifera as proxies using the Mg/Ca ratio (pdf!!)

And in the Meantime...
Antarctic Sea Ice May Be on the increase (yes, increase!)
Prepare for a New El Nino

Display:
something totally new. Fascinating stuff, Nomad.

You can't be me, I'm taken
by Sven Triloqvist on Wed Oct 4th, 2006 at 06:50:23 PM EST
From the article:

We conclude that global warming of more than 1°C, relative to 2000, will constitute ``dangerous'' climate change as judged from likely effects on sea level and extermination of species.

If, Hansen's conclusions are so obviously the result of flawed research methodology, why in heaven's name does he print such garbage, since it is, like you say (and I agree) counterproductive?  Is is due to ignorance, subversion or overzealousness?

I can swear there ain't no heaven but I pray there ain't no hell. _ Blood Sweat & Tears

by Gringo (stargazing camel at aoldotcom) on Wed Oct 4th, 2006 at 10:12:53 PM EST
Hansen et al base that statement on one hand of their conclusions of the figure discussed above (which I find not strong, but certainly a possibility) and on the other hand models of sea level rise and extermination and migration studies projected at a steep temperature increase - about which I know far less. It's IF THEN reasoning.

I wouldn't say the method is flawed; I would say we still  can't know whether it's correct. So it's not necessarily garbage; but overlooking the drawbacks of the method is intellectually dishonest to me. It could be his drive for change - he has certainly entered the spotlight for that. And good for him - but as said, if you built your arguments with weaknesses, they risk getting punched through.

by Nomad on Thu Oct 5th, 2006 at 02:41:01 PM EST
[ Parent ]
"I wouldn't say the method is flawed; I would say we still  can't know whether it's correct. So it's not necessarily garbage;.."

Agreed. I regret my poor choice of words.


I can swear there ain't no heaven but I pray there ain't no hell. _ Blood Sweat & Tears

by Gringo (stargazing camel at aoldotcom) on Thu Oct 5th, 2006 at 04:05:23 PM EST
[ Parent ]
Scientific papers like Hansen's go through a process of peer review when published in recognized journals. This means that two or three (anonymous) experts read the paper before it is published and approve it for publication. They may also request changes before it is published.

If they don't approve it, it doesn't get published. So it is unlikely that Hansen's techniques are not in accord with recognized methods used by others in the field. Can everyone be wrong? Possibly, but peer review is the best method currently available to prevent poor results from being published.

Policies not Politics
---- Daily Landscape

by rdf (robert.feinman@gmail.com) on Thu Oct 5th, 2006 at 09:15:05 AM EST
Recognized methods can be incorrect. Also, peer review is on the whole the best method available, but on an individual basis it is not infallible - not all papers get as much criticism as they might deserved.
by det on Thu Oct 5th, 2006 at 11:28:36 AM EST
[ Parent ]
I don't think Nomad's methodological criticism would be grounds for rejection. And, for laymen, it is interesting to have it pointed out that even the best accepted methods are not completely safe or even completely understood.

Those whom the Gods wish to destroy They first make mad. -- Euripides
by Migeru (migeru at eurotrib dot com) on Thu Oct 5th, 2006 at 11:36:41 AM EST
[ Parent ]
I can recall refereeing a paper, explaining that its main point was obvious garbage (the authors mistook instrument noise for a new, tremendously exciting, absurdly implausible phenomenon), and then seeing it published. This experience is, however, an outlier data point in the world of refereeing.

Words and ideas I offer here may be used freely and without attribution.
by technopolitical on Thu Oct 5th, 2006 at 10:44:36 PM EST
[ Parent ]
But it's a big paper - it covers a whole range of subjects, not just foraminifera proxies. If the peer reviewers are not in that field, they'd not immediately point it out.

And despite all of that, poor results, or even fraudulent results, still manage to get published, even in highly ranked journals. Remember the hubbub around Hu and his cloning experiments last year? Peer review is not perfect.

by Nomad on Thu Oct 5th, 2006 at 02:09:01 PM EST
[ Parent ]
What is the foraminifera proxy temperature between 1870 and 2005 and how does it compare with the sea surface temperature?

Those whom the Gods wish to destroy They first make mad. -- Euripides
by Migeru (migeru at eurotrib dot com) on Thu Oct 5th, 2006 at 09:29:03 AM EST
You'd thought they'd measure that? Wrong.

I've never been involved in a team with drilling a core or dredging up sediment traps (although I almost was, once) - but I know enough people who have. I'll ask why it so hard to take samples up to the most recent date. It makes so much sense to sample up to the most recent period so it allows overlapping the different time periods. Because I haven't seen this happening anywhere, I suspect there's a structural problem in sampling the core - but I'm not sure.

by Nomad on Thu Oct 5th, 2006 at 02:02:08 PM EST
[ Parent ]
So. You be a geologist, Nomad?

Did you see the big pleisiosaur find in Norway, announced today?

"When the abyss stares at me, it wets its pants." Brian Hopkins

by EricC on Thu Oct 5th, 2006 at 05:17:23 PM EST
[ Parent ]
They found beasties on Svalbard? Neat. I'm reading it now... BBC News has some not-really-spectacular pictures, here. Sounds like a nice find. About time, too: we need more stellar dinosaur collections like the Natural History museum in London and New York... Thanks for the tip!

I be a geologist, indeed. Hard rock and structural geology mostly, but I like to dabble in other fields as much as I can.

by Nomad on Thu Oct 5th, 2006 at 06:44:35 PM EST
[ Parent ]
Those can't be so-called "fossils", they're mere "figured stones" of no biological significance.
What is the nature of fossils? Are they, as the healthy common sense of the ancient Greeks appears to have led them to assume without hesitation, the remains of animals and plants? Or are they, as was so generally maintained in the fifteenth, sixteenth, and seventeenth centuries, mere figured stones, portions of mineral matter which have assumed the forms of leaves and shells and bones, just as those portions of mineral matter which we call crystals take on the form of regular geometrical solids? Or, again, are they, as others thought, the products of the germs of animals and of the seeds of plants which have lost their way, as it were, in the bowels of the earth, and have achieved only an imperfect and abortive development?

The Rise and Progress of Palæontology (1881)



Words and ideas I offer here may be used freely and without attribution.
by technopolitical on Thu Oct 5th, 2006 at 10:53:32 PM EST
[ Parent ]
I don't understand why you'd be quoting Thomas Huxley for that. "Figured stones" is a bit of an outdated concept, put lightly, and even Huxley uses fossils as the proper descriptor.


I will now sum up the results of this sketch of the rise and progress of palæontology. The whole fabric of palæontology is based upon two propositions: the first is, that fossils are the remains of animals and plants; and the second is, that the stratified rocks in which they are found are sedimentary deposits; and each of these propositions is founded upon the same axiom, that like effects imply like causes. If there is any cause competent to produce a fossil stem, or shell, or bone, except a living being, then palæontology has no founda[43]tion; if the stratification of the rocks is not the effect of such causes as at present produce stratification, we have no means of judging of the duration of past time, or of the order in which the forms of life have succeeded one another. But if these two propositions are granted, there is no escape, as it appears to me, from three very important conclusions. The first is that living matter has existed upon the earth for a vast length of time, certainly for millions of years. The second is that, during this lapse of time, the forms of living matter have undergone repeated changes, the effect of which has been that the animal and vegetable population, at any period of the earth's history, contains certain species which did not exist at some antecedent period, and others which ceased to exist at some subsequent period. The third is that, in the case of many groups of mammals and some of reptiles, in which one type can be followed through a considerable extent of geological time, the series of different forms by which the type is represented, at successive intervals of this time, is exactly such as it would be, if they had been produced by the gradual modification of the earliest forms of the series. These are facts of the history of the earth guaranteed by as good evidence as any facts in civil history.
by Nomad on Fri Oct 6th, 2006 at 08:21:57 AM EST
[ Parent ]
Sorry. A sidewise piece of snark, turned through a lateral angle half-way through.

I do think that the creationists should go back to the figured stones idea, though. It is so charming.

Words and ideas I offer here may be used freely and without attribution.

by technopolitical on Fri Oct 6th, 2006 at 02:41:13 PM EST
[ Parent ]
I'm never good at catching snarks, sorry. Perhaps we should be betting chocolate pie on this as well, like I did with afew. If I miss your snark for three times, chocolate pie on my bill.


I do think that the creationists should go back to the figured stones idea, though. It is so charming.

Right on!

by Nomad on Sat Oct 7th, 2006 at 07:36:53 AM EST
[ Parent ]
<head explodes>

Those whom the Gods wish to destroy They first make mad. -- Euripides
by Migeru (migeru at eurotrib dot com) on Thu Oct 5th, 2006 at 06:18:19 PM EST
[ Parent ]
What's the matter? Can't handle climate science?

I've done an hour of so of looking for other foraminifera proxy studies - apparently there are studies which concentrate on the past few millenia and look specifically at temperature increase - but those studies never go further than a few millenia. It's making me mad...

by Nomad on Thu Oct 5th, 2006 at 06:30:38 PM EST
[ Parent ]
Wait a minute... does this mean that Hansen et al. used an uncalibrated temperature scale to reconstruct SSTs prior to 1870?

The fact is that what we're experiencing right now is a top-down disaster. -Paul Krugman
by dvx (dvx.clt št gmail dotcom) on Fri Oct 6th, 2006 at 04:04:06 AM EST
[ Parent ]
I suppose it depends on how this has been determined
How does that work? Synopsised: People take a core of the ocean's sediment, sample it in tiny bits, filter it for specific foraminifera (which means: picking them by hand), crush the shells and run the powder through a spectrometer to establish the concentration of two elements in particular: Calcium (Ca) and Magnesium (Mg). Magnesium is an element which can substitute for calcium in the calcium carbonate shell but - and this is the clincher - the concentration of magnesium in the shells varies under certain conditions. One of them being: water temperature.


Those whom the Gods wish to destroy They first make mad. -- Euripides
by Migeru (migeru at eurotrib dot com) on Fri Oct 6th, 2006 at 04:26:43 AM EST
[ Parent ]
But that would be my problem with it: the calibration of the proxy temperature scale has some basic flaws left before one is able to compare them directly with measured temperatures. These difficulties are not even mentioned in the article. Also, note that Hansen et al. did not do the proxy measurements themselves: they used the data of others and combined that with the temperature data of their own.

There is research with other proxies (tree rings, ice cores, etc) that have the same problem: how well do the temperature scale delivered from the proxies measure up with the historical data from the thermometers? For tree rings, this has brought the birth of the divergence problem: some tree rings don't follow the temperature increase and others do. Which brings the question: how reliable are tree rings as a proxy measurement as a whole? Same here for foraminifera.

by Nomad on Fri Oct 6th, 2006 at 07:53:09 AM EST
[ Parent ]
Where does the temperature dependence of the Mg/Ca ratio come from? Is it just a difference influence of temperature on solubility or does it have to do with foraminifera metabolism?

Those whom the Gods wish to destroy They first make mad. -- Euripides
by Migeru (migeru at eurotrib dot com) on Fri Oct 6th, 2006 at 07:56:21 AM EST
[ Parent ]
I didn't think the foraminifera metabolism had much to do with it - we skirmish now to biomineralization which is in itself an intricate topic. But it has - it boosts the signal. Organic calcites have a lower Mg/Ca ratio than inorganic calcites. There definitely seems some control of biological mineralization - size, shape, spacing, type of mineral and element concentration seems to be partly wired, at least. So you need to take that into account. Is that temperature independent? I don't know and it sounds like an incredible pain to figure that one out.

Availability and effect of solubility curves are largely temperature dependent for the Mg/Ca ratio. Availability is hardly ever a problem. According to the Barker article: There's a reported 10% increase in Mg sensitivy per 1 degree C and the increase is exponential. Compare that to inorganic Mg uptake: you see a 3% increase in Mg sensitivity per 1 degree C.

Good questions. There's more in the overview of Barker et al, linked above.

by Nomad on Fri Oct 6th, 2006 at 08:59:42 AM EST
[ Parent ]
Organic calcites have a lower Mg/Ca ratio than inorganic calcites.

Got it the other way around: Organic calcites have a higher ratio, that is, there is more Mg uptake.

by Nomad on Fri Oct 6th, 2006 at 09:02:25 AM EST
[ Parent ]
According to the Barker article: There's a reported 10% increase in Mg sensitivy per 1 degree C and the increase is exponential.

Your compatriot J. H. van 't Hoff would have been able to tell you that the temperature dependent is exponential in 1/T (Van 't Hoff equation)

Those whom the Gods wish to destroy They first make mad. -- Euripides

by Migeru (migeru at eurotrib dot com) on Fri Oct 6th, 2006 at 09:28:29 AM EST
[ Parent ]
Of course! Great addition.
So, to sum it up, there's a
  1. thermodynamic driven uptake (translated in the solubility curves)
  2. biological driven uptake (which just mucks up with the chemical thermodynamics and seems to toss it out of the window which is of course not true)

Do we yet understand biological thermodynamics...?

To sum up the summary: everything is thermodynamics. (And that is what my professor always used to say.)

by Nomad on Fri Oct 6th, 2006 at 09:42:15 AM EST
[ Parent ]
I knew it was the Arrhenius Law, and I knew it was a Dutch Chemist, and I knew Arrhenius was Swedish... Arrhenius provided the statistical-mechanical explanation of 't Hoff's thermodynamical law.

Those whom the Gods wish to destroy They first make mad. -- Euripides
by Migeru (migeru at eurotrib dot com) on Fri Oct 6th, 2006 at 09:46:00 AM EST
[ Parent ]
I meant to say Wikipedia came to the rescue...

Those whom the Gods wish to destroy They first make mad. -- Euripides
by Migeru (migeru at eurotrib dot com) on Fri Oct 6th, 2006 at 09:46:26 AM EST
[ Parent ]
I didn't think the foraminifera metabolism had much to do with it - we skirmish now to biomineralization which is in itself an intricate topic. But it has - it boosts the signal.
This being a case of bioaccumulation into non-living tissue, biomagnification is to be expected.

Of course, hindsight is 20/20.

Those whom the Gods wish to destroy They first make mad. -- Euripides

by Migeru (migeru at eurotrib dot com) on Fri Oct 6th, 2006 at 09:53:45 AM EST
[ Parent ]
Carbon and oxygen isotopes which are lighter and hence enrgetically favourable, so far so good. Strontium replacements, all right, that comes with the system. But enhanced levels of Magnesium? What's the point in that? It probably has a point, or it wouldn't be there... The mind wonders. So you end up in a biological field looking for evolutionary fitness or function... Maddening.
by Nomad on Fri Oct 6th, 2006 at 11:19:43 AM EST
[ Parent ]
Maybe shell formation prefers magnesium but calcium is more abundant so it appears as though shell formation is about calcium and magnesium is the impurity?

Also note that the Alkaline Earth Metals are Berylium, Magnesium, Calcium, Strontium, Barium, Radium. Magnesium ans Calcium are actually quite similar chemically, but Magnesium is both lighter and more reactive than Calcium.


Those whom the Gods wish to destroy They first make mad. -- Euripides

by Migeru (migeru at eurotrib dot com) on Fri Oct 6th, 2006 at 11:29:55 AM EST
[ Parent ]
Wikipedia: Magnesium
Like its lower periodic table group neighbor calcium, magnesium reacts with water at room temperature, though it reacts much more slowly than calcium.

...

Too much magnesium in the [diet] may make it difficult for the body to absorb calcium.

...

Both of these alloys are recent developments in high temperature low creep magnesium alloys. The general strategy for such alloys is to form intermetallic precipitates at the grain boundaries, for example by adding mischmetal or calcium.


Calcium
Uses include: as an alloying agent used in the production of aluminium, beryllium, copper, lead, and magnesium alloys.

...

[Humphry Davy] worked with electrolysis throughout his life and also discovered/isolated magnesium, strontium and barium.

...

Calcium carbonate is the most common and least expensive calcium supplement. It can be difficult to digest and causes gas in some people. Taking magnesium with it can help to prevent constipation.

If you were Russian you would have more respect for the power of Mendeleyev's periodic table.

Those whom the Gods wish to destroy They first make mad. -- Euripides
by Migeru (migeru at eurotrib dot com) on Fri Oct 6th, 2006 at 11:39:01 AM EST
[ Parent ]
Well, actually, magnesium is more abundant than calcium in the ocean (by a factor of 3 by weight, of about a factor of 5 by concentration)...

Those whom the Gods wish to destroy They first make mad. -- Euripides
by Migeru (migeru at eurotrib dot com) on Fri Oct 6th, 2006 at 11:46:49 AM EST
[ Parent ]
Maybe one of the evolutionary purposes of shell formation is eliminating calcium as an impurity?
Magnesium is an essential element in biological systems. Magnesium occurs typically as the Mg2+ ion. It is an essential mineral nutrient for life[1][2][3] and is present in every cell type in every organism.


Those whom the Gods wish to destroy They first make mad. -- Euripides
by Migeru (migeru at eurotrib dot com) on Fri Oct 6th, 2006 at 11:53:54 AM EST
[ Parent ]
Foraminifera proxies may be a precise tool, but there is still a set of them that suffers up to this day from being inaccurate.

This is an important, basic, and misunderstood aspect of statistics. Thank you for pointing it out.

Those whom the Gods wish to destroy They first make mad. -- Euripides

by Migeru (migeru at eurotrib dot com) on Thu Oct 5th, 2006 at 09:31:14 AM EST


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