Temperature Record of the Last 1000 Years

[brazil84]

@LilShieste

Do you have any specific problems with the information provided by GIGObuster and jshore?

See my post #10.

[Czarcasm]

@brazil84

And just so we’re clear, the link is to an article that gives a certain impression about the hockey stick.

I am not claiming that the article proves or establishes that the hockey stick has been discredited. Although I imagine other posters will respond as if that had been my claim.

Not according to you. :dubious:

[brazil84]

@Czarcasm

Not according to you. :dubious:

I don’t understand your point at all.

[Czarcasm]

@brazil84

See my post #10.

That wasn’t a response to their posts- You posted another link and asked more questions.

[brazil84]

@Czarcasm

That wasn’t a response to their posts- You posted another link and asked more questions.

The thrust of the posts seems to be that “the hockey stick is still there.” i.e. even if Mann’s original paper had some problems, those problems have been fixed and his basic conclusion was correct.

To my mind, this is a valid point. If it is indeed the case that temperature in the second half of the 20th century is lots warmer than the last thousand years, then to me, it lends some support to the AGW hypothesis. Even if Mann fudged things back in 1998.

However, I do have some specific problems with the “hockey stick is still there” claim. Thus, my questions to jshore.

I invite you to discuss those questions civilly with me.

[brazil84]

@brazil84

I’ve been studying things and I have a few questions for you:

First, I found the following on one web site:

Do you agree with this?

Second, do you agree that the “hockey stick” has a strong inflection point right around where the date source switches from proxies to direct measurement?

Third, do you agree that there is a “divergence problem,” e.g. proxy data that doesn’t match up with recent instrumental temperature measurements? Do you agree that the IPCC Third Assessment Report contained a chart that omitted certain recent proxy data that diverged in this way?

Just to follow up on my questions, I would say the following:

First, I don’t believe that the NAS is the be-all end-all of AGW debate. However, the pro-AGW types seem to put a lot of stock in the NAS. Thus, if the NAS really indicated that a certain type of temperature proxy should not be used; and if the “hockey stick” relies on that type of temperature proxy, that’s a serious blow to the hockey stick. Unless I’m missing something.

Second, the “Splicing Problem” also appears very serious to me. If the elbow of the hockey stick occurs just about where the data shifts from proxy measurements to actual temperature measurements, the obvious inference is that it’s the data collection method that’s likely responsible for the sudden change and not an actual change in historic temperatures.

Last, the “Divergence Problem” would also appear to be quite serious. If the “hockey stick” relies on proxy measurements that don’t match up to historical temperatures that have been actually measured, it casts serious doubt on the proxy measurements from the past.

All in all, it looks to me like the “hockey stick” is BS. But I’m happy to consider arguments otherwise, especially responses to the 3 problems I described above.

[jshore]

brazil84: If I may summarize the style of your posts that I think Czarcasm and others are objecting to, it seems that what you do is to essentially fish for question on skeptic’s websites until you find one that people here can’t answer to your satisfaction and then you essentially say that this confirms pretty much what you thought about global warming. Do you see why we might have a problem with that?

As for your specific questions: I am really not up on the whole temperature reconstructions issue but I will tell you the limited amount that I do know.

In response to your 1st question, I think you ought to be very suspicious when people take a whole report like the NAS report and try to cobble together from this phrase here and that phrase there a conclusion that seems to contradict the actual conclusions in the report as clearly stated e.g. in the executive summary of the report itself. After all, if the NAS committee really thought reliance on strip-bark bristlecones made a reconstruction worthless and really knew that Mann’s work relied on strip-bark bristlecones, then why would they reach the conclusions that they did?

The NAS did express concerns that due to the weaker data quality as you go back beyond 400 years, the conclusions one can reach are necessarily weaker and the error bars larger…probably larger than one estimates by purely statistical methods. However, this is not the same as saying that the hockey stick is discredited. In fact, to the contrary they noted that many other studies have now supported the basic claim that it is warmer in the late 20th century than at any time in the last millenium (while some of the newer reconstructions do show more variability…with a more pronounced MWP and Little Ice Age although, as the IPCC report notes, this is not because they find the MWP to be warmer than Mann et al estimated but rather because they find the LIA to be cooler).

However, to be honest, this remains an active area of study and until more different independent proxies lead to the same conclusions (and there is more convergence amongst the various reconstructions), there will remain legitimate areas of debate, which is natural for many fields of science, particularly one that has to rely on such indirect ways of ascertaining the data.

In response to your second and third questions: I know there have been some questions about how well the proxies have followed the modern temperature rise. A lot of the problem is that much of this rise has occurred over just the last 25 years or so and many of the proxies do not extend to this modern time. It is also worth noting that Osburn and Briffa in their paper looked solely at proxies and did not make any attempt to splice the modern instrumental temperature onto them at all and they concluded “The most significant and longest duration feature during the last 1200 years is the geographical extent of warmth in the middle to late 20th century,” a conclusion that is robust to the removal of up to any 3 of the 14 proxy data sets used.

Finally, it is worth re-emphasizing that the evidence that the current warming is anomalous over the last millenium or so is only one piece of evidence…and the most circumstantial (and difficult to substantiate) one. Other lines of evidence consider the actual mechanistic understanding of how CO2 leads to warming, compare the pattern of the warming (e.g., warming troposphere and cooling stratosphere) to what would be expected from various mechanisms, and consider whether other potential mechanisms (such as solar forcing) have even been acting in the right direction over the last few decades (which, it seems they haven’t).

[brazil84]

@jshore

brazil84: If I may summarize the style of your posts that I think Czarcasm and others are objecting to, it seems that what you do is to essentially fish for question on skeptic’s websites until you find one that people here can’t answer to your satisfaction and then you essentially say that this confirms pretty much what you thought about global warming.

That’s not my practice. Anyway, as I said in the first post, I will consider any arguments in good faith.

Do you see why we might have a problem with that?

Not really. If some skeptic’s web site has a compelling criticism of the hockey stick, and there’s no good response, then what does it matter who raised it and why?

As for your specific questions: I am really not up on the whole temperature reconstructions issue but I will tell you the limited amount that I do know.

In response to your 1st question, I think you ought to be very suspicious when people take a whole report like the NAS report and try to cobble together from this phrase here and that phrase there a conclusion that seems to contradict the actual conclusions in the report as clearly stated e.g. in the executive summary of the report itself.

Of course I’m suspicious. That’s why I asked for your response.

After all, if the NAS committee really thought reliance on strip-bark bristlecones made a reconstruction worthless and really knew that Mann’s work relied on strip-bark bristlecones, then why would they reach the conclusions that they did?

It seems like the NAS committee didn’t particulary credit Mann’s work. They acknowledged criticisms of some of his methods and pointed out areas where other research supported his conclusions.

For example, they pointed out that other research supported the conclusion that temperatures are warmer now than in the past few hundred years. Duh. People on both sides of the debate agree that there was a “little ice age.”

If Mann’s temperature reconstruction had been based on tea-leaf reading, the NAS committee could have made essentially the same points.

Anyway, the real question is this: If the NAS committee said that researchers should avoid making use of strip bark samples in doing temperature reconstructions, do any researchers still make use of such samples? And if so, why?

In response to your second and third questions: I know there have been some questions about how well the proxies have followed the modern temperature rise. A lot of the problem is that much of this rise has occurred over just the last 25 years or so and many of the proxies do not extend to this modern time.

That’s a problem for people who insist that we rely on proxies. Not for those who question them. Anyway, like McIntyre asks on his web site, why haven’t those proxies been updated?

It is also worth noting that Osburn and Briffa in their paper looked solely at proxies and did not make any attempt to splice the modern instrumental temperature onto them at all and they concluded “The most significant and longest duration feature during the last 1200 years is the geographical extent of warmth in the middle to late 20th century,” a conclusion that is robust to the removal of up to any 3 of the 14 proxy data sets used.

I looked at the paper and didn’t notice any hockey stick. It seems to me that if you get rid of splicing, most of the hockey stick goes away. Anyway, do you agree that that paper relies on strip bark bristlecones? Skeptics seem to say that it does. If the NAS said that use of such samples should be avoided, why would respected climatologists still be using them?

Finally, it is worth re-emphasizing that the evidence that the current warming is anomalous over the last millenium or so is only one piece of evidence…and the most circumstantial (and difficult to substantiate) one.

This thread is about the hockey stick. If you would like to start a thread about AGW in general, I would be happy to participate.

[BrainGlutton]

Wikipedia article on the "Hockey-stick controversy.
From Scientific American, March 2005:

The work of Mann and his colleagues achieved special prominence in 2001. That is when the Intergovernmental Panel on Climate Change (IPCC), an international body of climate experts, placed the hockey-stick chart in the Summary for Policymakers section of the panel’s Third Assessment Report. (Mann also co-authored one of the chapters in the report.) It thereby elevated the hockey stick to iconic status–as well as making it a bull’s-eye. A community skeptical of human-induced warming argued that Mann’s data points were too sparse to constitute a true picture, or that his raw data were numerically suspicious, or that they could not reproduce his results with the data he had used. Take down Mann, it seemed, and the rest of the IPCC’s conclusions about anthropogenic climate change would follow.

That led to “unjustified attack after unjustified attack,” complains climatologist Gavin A. Schmidt of the NASA Goddard Institute for Space Studies. Although questions in the field abound about how, for example, tree-ring data are compiled, many of those attacking Mann’s work, Schmidt claims, have had a priori opinions that the work must be wrong. “Most scientists would have left the field long ago, but Mike is fighting back with a tenacity I find admirable,” Schmidt says. One of Mann’s more public punch backs took place in July 2003, when he defended his views before a congressional committee led by Senator James M. Inhofe of Oklahoma, who has called global warming a “hoax.” “I left that meeting having demonstrated what the mainstream views on climate science are,” Mann asserts.

More recently, Mann battled back in a 2004 corrigendum in the journal Nature, in which he clarified the presentation of his data. He has also shown how errors on the part of his attackers led to their specific results. For instance, skeptics often cite the Little Ice Age and Medieval Warming Period as pieces of evidence not reflected in the hockey stick, yet these extremes are examples of regional, not global, phenomena. “From an intellectual point of view, these contrarians are pathetic, because there’s no scientific validity to their arguments whatsoever,” Mann says. “But they’re very skilled at deducing what sorts of disingenuous arguments and untruths are likely to be believable to the public that doesn’t know better.”

[brazil84]

It thereby elevated the hockey stick to iconic status–as well as making it a bull’s-eye. A community skeptical of human-induced warming argued that Mann’s data points were too sparse to constitute a true picture, or that his raw data were numerically suspicious, or that they could not reproduce his results with the data he had used. Take down Mann, it seemed, and the rest of the IPCC’s conclusions about anthropogenic climate change would follow.

It seems like a common theme in the AGW debate to attack peoples’ motivations rather than to attack their arguments. Motivations are interesting, but substance is a lot more important in my opinion.

For instance, skeptics often cite the Little Ice Age and Medieval Warming Period as pieces of evidence not reflected in the hockey stick, yet these extremes are examples of regional, not global, phenomena. “From an intellectual point of view, these contrarians are pathetic, because there’s no scientific validity to their arguments whatsoever,”

That’s a pretty strong claim. Given that the medieval warm period (according to Wikipedia) took place in the North Atlantic region; and given that the “hockey stick” was supposed to represent the northern hemisphere, it would seem to follow that (according to Mann) (1) the other 2/3 of the northern hemisphere were anomalously cold during the medieval warm period; and (2) there no validity whatsoever to any claim to the contrary.

Would you like to defend that position?

[BrainGlutton]

@brazil84

That’s a pretty strong claim. Given that the medieval warm period (according to Wikipedia) took place in the North Atlantic region; and given that the “hockey stick” was supposed to represent the northern hemisphere, it would seem to follow that (according to Mann) (1) the other 2/3 of the northern hemisphere were anomalously cold during the medieval warm period; and (2) there no validity whatsoever to any claim to the contrary.

Would you like to defend that position?

Here’s the Hockey Stick Chart – you can see for itself how it describes Northern Hemisphere temperatures in the periods in question. But it is wise to give more attention to the right end of the chart.

Same with this chart comparing different estimates.

[brazil84]

@BrainGlutton

Here’s the Hockey Stick Chart – you can see for itself how it describes Northern Hemisphere temperatures in the periods in question. But it is wise to give more attention to the right end of the chart.

Same with this chart comparing different estimates.

As mentioned earlier, I think there are at least 3 serious problems with the hockey stick graph: The “bristlecone” problem; the “splicing” problem; and the “divergence” problem. Any one of these problems casts a lot of doubt on the graph.

Do you think that each of these objections is completely lacking in scientific merit? If so, why?

[LilShieste]

@brazil84

It seems like a common theme in the AGW debate to attack peoples’ motivations rather than to attack their arguments.

Indeed.

LilShieste

[brazil84]

@LilShieste

Indeed.

LilShieste

I don’t understand your point. In the post you link to, somebody else had raised the issue of motivations and I merely responded.

What would have been more problematic is if I had not raised the splicing, bristlecone, or divergence problems, and simply dismissed Mann as somebody who’s trying to get attention, funding, and tenure.

Anyway, like I said, motivations are interesting. But they are less important than substance.

[BrainGlutton]

@brazil84

I don’t understand your point. In the post you link to, somebody else had raised the issue of motivations and I merely responded.

The difference, of course, is that attributing non-scientific, i.e., financial, motivations to the AGW-skepticism faction makes sense. The reverse does not. As has been pointed out to you in these threads many times, I’m sure. It isn’t the “warmists” who fund phony astroturf organizations and think-tanks.

Mann thinks that the attacks will continue, because many skeptics, such as the Greening Earth Society and the Tech Central Station Web site, obtain funds from petroleum interests. “As long as they think it works and they’ve got unlimited money to perpetuate their disinformation campaign,” Mann believes, “I imagine it will go on, just as it went on for years and years with tobacco until it was no longer tenable–in fact, it became perjurable to get up in a public forum and claim that there was no science” behind the health hazards of smoking.

[brazil84]

@BrainGlutton

The difference, of course, is that attributing non-scientific, i.e., financial, motivations to the AGW-skepticism faction makes sense. The reverse does not. As has been pointed out to you in these threads many times, I’m sure. It isn’t the “warmists” who fund phony astroturf organizations and think-tanks.

I disagree, but you’ve wandered beyond the scope of this thread.

If you want to start a new thread arguing that AGW-skeptics should not be trusted because their motives are suspect; and the pro-AGW people have motives that are pure, I promise to participate.

This thread is about the merits of the hockey stick graph.

As mentioned earlier, I think there are at least 3 serious problems with the hockey stick graph: The “bristlecone” problem; the “splicing” problem; and the “divergence” problem. Any one of these problems casts a lot of doubt on the graph.

Do you think that each of these objections is completely lacking in scientific merit? If so, why?

[BrainGlutton]

@brazil84

First, I found the following on one web site:

The NAS Panel found in one place that “strip-bark samples” (which Graybill sought out in his bristlecone collections) should “not be used”. They also reported that the MBH results were “strongly dependent” on “Great Basin data” - code for bristlecones and stated, somewhat inconsistently, that this should be reflected in confidence interval calculations.

Do you agree with this?

Don’t have the scientific knowledge to evaluate whether that is a serious objection, but the general convergence of measurements taken by different methods is impressive.

@brazil84

Second, do you agree that the “hockey stick” has a strong inflection point right around where the date source switches from proxies to direct measurement?

If the AGW hypothesis is correct, then that is only to be expected, the scientific revolution necessarily coinciding with the industrial revolution.

@brazil84

Third, do you agree that there is a “divergence problem,” e.g. proxy data that doesn’t match up with recent instrumental temperature measurements? Do you agree that the IPCC Third Assessment Report contained a chart that omitted certain recent proxy data that diverged in this way?

Why should I? Cite? (And be careful which you choose.)

[jshore]

@brazil84

If you want to start a new thread arguing that AGW-skeptics should not be trusted because their motives are suspect; and the pro-AGW people have motives that are pure, I promise to participate.

That’s a very poor characterization of the argument. The argument is that in order to question the motives of the “pro-AGW people”, you essentially have to explain why the IPCC, the NAS, and in fact essentially all the major scientific organizations in the major nations have been hijacked by these motives that have led them to abandon their scientific principles. To question the motives of the AGW-skeptics, you only have to ask why a few scientists, most with very spartan publishing records in the field, and many with very open affiliations to right-wing think-tanks and/or the fossil fuel industry might not have the purest of intentions.

[jshore]

@brazil84

Not really. If some skeptic’s web site has a compelling criticism of the hockey stick, and there’s no good response, then what does it matter who raised it and why?

Okay, I will spell it out for you: If you go mining for arguments from skeptics websites, you are bound to find some that we will be unable to answer to your satisfaction particularly given that none of us here are trained climate scientists. (And, beyond the issue that you are asking people who are not trained climate scientists, let’s face it, in any field of science, there will always be some mysterious that cannot be explained within the current theory.)

It seems like the NAS committee didn’t particulary credit Mann’s work. They acknowledged criticisms of some of his methods and pointed out areas where other research supported his conclusions.

For example, they pointed out that other research supported the conclusion that temperatures are warmer now than in the past few hundred years. Duh. People on both sides of the debate agree that there was a “little ice age.”

If Mann’s temperature reconstruction had been based on tea-leaf reading, the NAS committee could have made essentially the same points.

You are mischaracterizing what they said. What they said was that the statement that it was now warmer than it has been in the past few hundred years is strongly supported by a broad array of evidence. Then they noted that going back further, the amount of proxy evidence available is less and the uncertainties are greater but that other research has supported the conclusion that it is now warmer than at any time in the last millenium. Or, to quote directly,

• It can be said with a high level of confidence that global mean surface temperature was higher during the last few decades of the 20th century than during any comparable period during the preceding four centuries. This statement is justified by the consistency of the evidence from a wide variety of geographically diverse proxies.
• Less confidence can be placed in large-scale surface temperature reconstructions for the period from A.D. 900 to 1600. Presently available proxy evidence indicates that temperatures at many, but not all, individual locations were higher during the past 25 years than during any period of comparable length since A.D. 900. The uncertainties associated with reconstructing hemispheric mean or global mean temperatures from these data increase substantially backward in time through this period and are not yet fully quantified.

…

The basic conclusion of Mann et al. (1998, 1999) was that the late 20th century warmth in the Northern Hemisphere was unprecedented during at least the last 1,000 years. This conclusion has subsequently been supported by an array of evidence that includes both additional large-scale surface temperature reconstructions and pronounced changes in a variety of local proxy indicators, such as melting on ice caps and the retreat of glaciers around the world, which in many cases appear to be unprecedented during at least the last 2,000 years. Not all individual proxy records indicate that the recent warmth is unprecedented, although a larger fraction of geographicallydiverse sites experienced exceptional warmth during the late 20th century than during any other extended period from A.D. 900 onward.

Based on the analyses presented in the original papers by Mann et al. and this newer supporting evidence, the committee finds it plausible that the Northern Hemisphere was warmer during the last few decades of the 20th century than during any comparable period over the preceding millennium. The substantial uncertainties currently present in the quantitative assessment of large-scale surface temperature changes prior to about A.D. 1600 lower our confidence in this conclusion compared to the high level of confidence we place in the Little Ice Age cooling and 20th century warming. Even less confidence can be placed in the original conclusions by Mann et al. (1999) that “the 1990s are likely the warmest decade, and 1998 the warmest year, in at least a millennium” because the uncertainties inherent in temperature reconstructions for individual years and decades are larger than those for longer time periods and because not all of the available proxies record temperature information on such short timescales.

Surface temperature reconstructions for periods prior to the industrial era are only one of multiple lines of evidence supporting the conclusion that climatic warming is occurring in response to human activities, and they are not the primary evidence.

@brazil64

Anyway, the real question is this: If the NAS committee said that researchers should avoid making use of strip bark samples in doing temperature reconstructions, do any researchers still make use of such samples? And if so, why?

The only relevant quote that I can find when I search for “strip” in the NAS report is this statement:

The possibility that increasing tree ring widths in modern times might be driven by increasing atmospheric carbon dioxide (CO2) concentrations, rather than increasing temperatures, was first proposed by LaMarche et al. (1984) for bristlecone pines (Pinus longaeva) in the White Mountains of California. In old age these trees can assume a “strip-bark” form, characterized by a band of trunk that remains alive and continues to grow after the rest of the stem has died. Such trees are sensitive to higher atmospheric CO2 concentrations (Graybill and Idso 1993), possibly because of greater water-use efficiency (Knapp et al. 2001, Bunn et al. 2003) or different carbon partitioning among tree parts (Tang et al. 1999). Support for a direct CO2 influence on tree ring records extracted from “full-bark” trees is less conclusive. Increasing mean ring width was reported for Pinus cembra from the central Alps growing well below treeline (Nicolussi et al. 1995). Free-Air CO2 Enrichment (FACE) data for conifer plantations in the Duke Forest (Hamilton et al. 2002) and at the alpine treeline (Hättenschwiler et al. 2002) also showed increased tree growth after exposure to atmospheric CO2 concentrations about 50 percent greater than present. On the other hand, no convincing evidence for such effect was found in conifer tree ring records from the Sierra Nevada in California (Graumlich 1991) or the Rocky Mountains in Colorado (Kienast and
Luxmoore 1988). Further evidence comes from a recent review of data for mature trees in four climatic zones, which concluded that pine growth at the treeline is limited by factors other than carbon (Körner 2003). While “strip-bark” samples should be avoided for temperature reconstructions, attention should also be paid to the confounding effects of anthropogenic nitrogen deposition (Vitousek et al. 1997), since the nutrient conditions of the soil determine wood growth response to increased atmospheric CO2 (Kostiainen et al. 2004). However, in forest areas below the treeline where modern nitrogen input could be expected to influence dendroclimatic records, such as Scotland (Hughes et al. 1984) and Maine (Conkey 1986), the relationship between temperature and tree ring parameters was stable over time.

This to me does not amount to a statement that any collection of tree ring chronologies that include in them any strip bark samples make the whole collection completely worthless. I don’t actually know to what extent the various tree ring chronologies might have included any strip bark samples in them.

In any field of science there will always be various concerns about data quality. However, that such concerns exist does not necessarily render the studies that use them worthless. It does mean that it would be worthwhile to do more studying of these effects and to collect new tree ring samples where more care is taken to avoid any strip-bark samples, for example.

However, in essence, by arguing these points and trying to say that they somehow outweigh the overall conclusions that the NAS report clearly came to, one is essentially overweighting these concerns since they are presumably already reflected in the conclusions. In fact, if you look at the number of studies that have now demonstrated that it is warmer now than it was anytime over the last millenium, it would be hard to see why the NAS would not have come to a much stronger conclusion endorsingthe correctness of this claim were it not for such mitigating concerns involving data quality and the like.

[brazil84]

@BrainGlutton

Don’t have the scientific knowledge to evaluate whether that is a serious objection, but the general convergence of measurements taken by different methods is impressive.

I disagree. The results depend a lot on which proxies you choose.

For example, a paper was published the other day that purported to reconstruct a global temperature using all proxy measures ments that were not based on tree rings (and which had more than 20 values in the last 2000 years):

http://www.ncasi.org/publications/Detail.aspx?id=3025

There’s no hockey stick and there is a medieval warm period that’s significantly warmer than today.

If the AGW hypothesis is correct, then that is only to be expected, the scientific revolution necessarily coinciding with the industrial revolution.

The “elbow” of the hockey stick occurs around the turn of the last century. By that time, CO2 concentrations had increased from about 280ppm to 300ppm. (According to these charts: http://www.lib.utah.edu/services/prog/gould/1998/Figure_6.gif
http://www.environment.gov.au/soe/2001/publications/theme-reports/atmosphere/images/atfg051.gif

)

I don’t think that even Michael Mann would argue that such an increase in CO2 triggered a rapid increase in temperature.

Why should I? Cite? (And be careful which you choose.)

See Post #16

And by the way, my question still stands: Are you saying that each of my objections is completely lacking in scientific merit?