Medieval Climate Not So Hot

University Of Arizona ^ | 10-20-2003 | U of Arizona

[editor-surveyor]

Certified Clap-Trap.

[E.G.C.]

BTTT!!!!!!

[E.G.C.]

BTTT!!!!!!

[Dan Evans]

Tree rings are a lousy proxy for temperature. John Daly explains:

"Tree rings are the primary proxy behind the `Hockey Stick', particularly the earlier part of the millennium. Tree rings are only laid during the growing season, not the whole year, and so they tell us little or nothing about annual climate. For example, this year (2000) there was a warm winter and early spring in the north-eastern USA, followed by an unusually cool summer and fall. Since the two events are largely self-cancelling, the year may finish as fairly average, but the tree rings would only record the cool summer and thus give a completely false impression of the full-year temperature. Tree rings do not even record night temperatures since photosynthesis only occurs in the daytime. Yet winter and night temperatures are an essential component of what we understand by the concept `annual mean temperature'.

All a tree ring can tell us is whether the combined micro-environmental conditions during the growing season were favourable to tree growth or not. This is because tree rings are influenced by numerous factors other than temperature, such as rainfall, sunlight, cloudiness, pests, competition, forest fires, soil nutrients, frosts and snow duration. Thus they are not even a good daytime temperature proxy for the few months of the growing season. Other proxies such as isotopes in coral, ice, minerals and sediments are vastly superior.

Trees only grow on land. Since 71% of the planet is covered by oceans, seas and lakes, tree rings can tell us nothing about the maritime climate, even though the oceans are known to be the prime determinants of climate conditions throughout the world.

In other words, historical climate simply cannot be described without taking into account the winter and adjacent months temperatures, night-time temperatures, and ocean sea surface temperatures. Tree rings, no matter how carefully they are measured and examined, cannot provide information on any of these key parameters, and are a doubtful proxy even for daytime temperatures on land in summer.

A final weakness arises when calibrating the tree rings against temperature. When measuring the width or density of a tree ring, exactly what temperature is represented by that measurement? This can only be determined by calibrating recently laid rings against known temperatures that existed at the time. Even this is problematic as the `known temperatures' can mean using a temperature series seriously contaminated by heat island and other local errors. If the calibrating temperatures are wrong, the whole tree ring temperature reconstruction for the distant past is also compromised.

There are many sub-specialties within the greenhouse sciences, `dendrochronology' (study of tree rings) being one of them. That particular sub-branch has both prospered and been highly successful in projecting itself to the broader climatic community on the basis of what is a very weak proxy.

In respect of Europe and Greenland, the IPCC and `National Assessment' do not challenge the existence of the Medieval Warm Period and Little Ice Age as they are too well recorded in other proxy indicators and historical accounts of the time. Instead, these events are now presented as being purely local to Europe and Greenland, but completely absent elsewhere in the world.

In general, the greenhouse industry disregards historical evidence, claiming them to be merely `anecdotes'. However, the idea that historical evidence can be easily dismissed as `anecdotes' in favor of questionable proxies like tree rings is to suggest that professional historians cannot be trusted to be objective.

Objectivity comes from how the evidence is treated, not the nature of the evidence itself. Historians can be just as objective as any scientist. Indeed most of them regard their work as science. As a prominent Finnish scientist remarked about a historical military event in his country's distant history, "if `anecdotal' ice is thick enough to carry a whole army, we can infer the ice was both thick and durable as an objective conclusion based on a documented historical fact."

Similar inferences can be made elsewhere in the world. For example, if whole populations suffered from drought-induced famine, we can infer a reduced rainfall. We don't need the proxies to tell us - indeed they might even mislead us. When a society is ravaged by great floods, we can infer increased precipitation. When the Polynesians were able to populate the Pacific Islands by outrigger boats, we can make climate inferences there too.

The fact that the greenhouse sciences were reluctant to declare the Medieval Warm Period and Little Ice Age as non-events in Europe suggests that the historical evidence was too overwhelming to make selected proxies believable. Such a claim for Europe would have been met with derision. While greenhouse science may regard proxies as being more objective than historical `anecdotes', that viewpoint is only shared among that peer group. The wider academic community, governments, and public opinion (the most important peer group of all) will give much more credibility to well-researched historical evidence.

If the IPCC were genuine about the need for full information about millennial climate, they would involve historians everywhere to research their resources to determine past climates as observed and experienced by human societies. The fear of some global warming proponents is that the historians would indeed find the Medieval Warm Period and Little Ice Age all over the world and that governments and public opinion would accept the historical accounts over tree rings."
http://www.john-daly.com/hockey/hockey.htm

[Wonder Warthog]

"FYI, The tree ring chronology is now over 10,000 years long. This guy, Mike Baillie, has done some amazing work with this data."

I thought they had pushed it back further than that?? I only keep in touch with dendrochronology somewhat peripherally to my interest in isotope age dating. Once upon a time I used to do some sample prep for C-14 dating, and in a totally unrelated research connection (unrelated to C-14 dating, that is) had a chance to work for a short time with Willard Libby (who developed C-14 dating). A genius of a man even in his later years (I think he was over eighty when I worked with him).

[Carry_Okie]

Uh, the calibration is inherent in the ring patterns themselves. Individual rings may be wider or narrower due to variations in climate, but there is always "one set of rings per year".

There are exceptions to this "one set of rings per year" rule. I know for a fact that redwood can have more than one depending upon weather variation.

Scientists still haven't properly characterized how tree growth depends upon the interactions between temperature, available water (both from precipitation and ground seeps), and sunlight. I know people personally who are still doing that work, tracking tree growth against these variables on a daily basis. There is NO WAY these people can infer climate from tree rings or pollen strata without allowing for significant errors.

The report sounds like crap. Best to check out who paid for it.

[polemikos]

I think there's a a significant correlation between climatology programs and global warming. Increased instrumentation of weather attributes is causing an increase in measured temperatures worldwide. /sarcasm

[AFPhys]

I don't think I'll even bother to look further into this "study". There have been at least five others which contend that the Medieval Warming WAS global and persistent, several of which have used data analogous so that which is apparently in this "study". Sorry, guys --- I don't buy it.
I suppose they find that the "Little Ice Age" was also an event which has only local ramifications.

[Wonder Warthog]

"There are exceptions to this "one set of rings per year" rule. I know for a fact that redwood can have more than one depending upon weather variation."

Which is why any data set must contain a large number of elements to overcome this sort of problem.

Scientists still haven't properly characterized how tree growth depends upon the interactions between temperature, available water (both from precipitation and ground seeps), and sunlight. I know people personally who are still doing that work, tracking tree growth against these variables on a daily basis. There is NO WAY these people can infer climate from tree rings or pollen strata without allowing for significant errors.

Of course there are "significant errors". I'm sure the actual scientific paper contains at least "some" indication of the magnitude of the possible errors (otherwise it should never have been published). I suspect whatever reporter or publicist generated the press release ignored mentioning them.

"The report sounds like crap. Best to check out who paid for it."

Agreed, but not for dendrochronology or isotope ratio reasons. Their assertion that volcanos can account for "localized warming" flies in the face of all the science "I" know about with respect to volcano/climatology interactions.

[gatex]

Temperature data from Vostok ice cores---BP = before present

Temperature appears to cycle every 100,000 years.

link to graph = http://cdiac.esd.ornl.gov/trends/temp/vostok/jouz_tem.htm

[Carry_Okie]

Of course there are "significant errors". I'm sure the actual scientific paper contains at least "some" indication of the magnitude of the possible errors (otherwise it should never have been published). I suspect whatever reporter or publicist generated the press release ignored mentioning them.

When the cumulative error tolerance wildly exceeds the variation of the variable under study, particularly when so many different inputs can confound the outputs, to make a strong conclusion based upon that kind of data is more than suspect; it's whoring for grant money.

Agreed, but not for dendrochronology or isotope ratio reasons. Their assertion that volcanos can account for "localized warming" flies in the face of all the science "I" know about with respect to volcano/climatology interactions.

Yup. It seems to me that dendochronology's most useful contribution is when used to consider the applicability of crop failures, pestilence, floods, or other environmental singularities in historical events. Consider Exodus or the fall of Rome.

[cogitator]

Paleotemperatures are not determined using stable oxygen isotopes in tree rings (though stable oxygen isotopes are used for paleotemperature determination in carbonate sediments and ice, to name two).

Climate Change from Earth Temperatures: The Big Integrator

"Longer-term climatic variations, on the other hand, have been inferred from a variety of proxy climate indicators including growth rings in trees. Because tree growth depends partly on temperature, the width of an individual tree ring can be used to identify paleotemperature trends. This method has a potential for annual time resolution over the past millennium. The most serious limitation of dendroclimatology arises from the complex nature of tree growth itself and its interaction with the surrounding environment. The average ring width for a given tree is a nonlinear function of a large number of variables including the species and age of the tree, the amount of usable nutrients in the surrounding soil and a large number of interacting climatic variables (e.g. amount of insolation reaching the tree, temperature and precipitation regimes and their annual variations). Therefore, reduced (or increased) tree growth can arise from several combinations of different climatic conditions."

So how does a researcher distinguish between temperature and other factors? By choosing the right tree-ring chronologies. Trees at higher elevations (near timberline) provide larger temperature signals, and there is also a better correlation of latewood density with temperature than just with tree-ring width.

Paleoclimatologists have a lot of methods at their disposal (I was going to say "tricks up their sleeve", but these aren't tricks).

"

[cogitator]

Perhaps Mr. Daly might wish to consult with the experts:

The Laboratory for Tree-Ring Research

A guide to dendrochronology for educators

It's always too bad that Mr. Daly disparages something that he doesn't understand very well.

[Dan Evans]

Mr. Daly understands tree-ring data. He understands the global warming industry better than anyone. It is an evil, left-wing, political movement. It is evil because its proponents care more about advancing their assertions than they care about the truth. It is evil because it is driven by the greed of politicians looking for an excuse to tax. It is evil because the "scientists" who advance it are interested only in their careers, not in science.

Any rational thinking person when confronted with all of the data will come to the conclusion that global climate is driven by the sun.

Close to 20,000 good people with doctorates have signed a petition denouncing the theory that global warming is a threat.

[cogitator]

I'm currently involved on another thread with what I expect will be a long discussion of real global warming science, as opposed to Mr. Daly's opinions. If you're interested, I'll post a link to the thread in my next reply to you. Feel free to follow along.

Any rational thinking person when confronted with all of the data will come to the conclusion that global climate is driven by the sun.

If we didn't have the Sun, we wouldn't have climate. But climate change is driven by many other factors. Solar variability has been factored in, and measured. It's not a factor right now.

Close to 20,000 good people with doctorates have signed a petition denouncing the theory that global warming is a threat.

The petition was accompanied by a paper that was made to look like a Proceedings of the National Academy of Sciences (PNAS) paper, when in fact it was a private publication. The NAS had to publish a public declaration distancing themselves from this hoax and making sure that the public was aware that they were not involved with it.

[cogitator]

Rushing to Judgement: Global warming questioned (long but good)

[Carry_Okie]

I'm currently involved on another thread with what I expect will be a long discussion of real global warming science, as opposed to Mr. Daly's opinions.

Mr. Daly has made some damned good observations. All of us have our opinions.

Solar variability has been factored in, and measured. It's not a factor right now.

That is not a very scientific statement. You are claiming way too much for what is known at this point. Solar variation may have been measured (although not for very long) but it hasn't been "factored in" except by those looking to make more claims than is warranted. Considering how long we have been hearing claims of global warming without considering these variables, that is is the same claque of people making those claims and in the same publications with similar politics on the editorial boards, and that it is the same interested parties paying for the work, and I have my suspicions as any rational person would.

First, historical solar variation hasn't been measured long enough to form any kind of baseline, there are theories positing solar cycles and even some measurements, but not much more than that. Second, the spectral interactions between solar outputs and terrestrial response variables are still being posited; they haven't been thoroughly characterized. Hell, people are still discovering new absorptive mechanics. So although we now have a measure of understanding of solar outputs, we still don't have a good idea of what they portend or what the various responses are by frequency. Third, the role played by external inputs, meteorites, volcanoes, and asteriods is horribly sketchy and confounds all the rest of the historical data. Then there is all the feedback involved in how those adsorptive and reflective mechnanics work.

It's the feedback and the singularities that are the bugaboo. One can't characterize the system against historical data without them. The number of elements in that system is so large that the errors accumulate to the point of absurdity. Some good work is being done, along with some trash, as we see here.

[Wonder Warthog]

"Paleotemperatures are not determined using stable oxygen isotopes in tree rings (though stable oxygen isotopes are used for paleotemperature determination in carbonate sediments and ice, to name two)."

What prevents doing so?? It seems to me that determining the 016/018 ratio in cellulose and/or lignin would be just about the perfect approach to measuring the relevant temperature effect(s). I'm well aware of the carbonate sediments/ice core studies, so was assuming that a similar approach would apply to tree rings.

"So how does a researcher distinguish between temperature and other factors? By choosing the right tree-ring chronologies.

In other words, it allows you "global warmers" to cherry-pick the data to support your prejudices.

Sorry, but as AFPhys says, there are already multiple studies using similar methodology which say that the Medieval Warm Period was global in extent.

[PoorMuttly]

These theories' flawed flaws are flawed.

Ain't science great ?!!

[cogitator]

In answer to your question about stable oxygen isotopes in tree rings, my answer is: I don't know. But the process of building cellulose is probably different than the process of biomineralization (for CaCO3), and certainly is different than ice formation. Beyond that, ask the experts, not me. Seems like it could be done with isotope mass spectrometry.

With regards to the Medieval Warm period studies, the debate is raging at the scientific level (which is one reason that the study highlighted by the press release at the top of this thread was published, written by several tree-ring experts at the Laboratory for Tree Ring Studies, link to their home page already posted). They, and others, have responded to an article published earlier this year. Scientific denouncement of this paper has been rather widespread. But that's science: thesis vs. antithesis results in synthesis (eventually).