Temperature Record of the Last 1000 Years

[brazil84]

We’ve all heard of the infamous “hockey stick” graph that showed little temperature change from years 1000 to 1900; followed by a sharp rise between 1900 and 2000.

I had been under the impression that the “hockey stick” has been pretty much discredited. That in fact there is compelling evidence for a “medieval warm period” and a “little ice age.” And that the “hockey stick” is the result of flawed analysis.

Please educate me. I promise to consider your arguments in good faith.

[Czarcasm]

@brazil84

I had been under the impression that the “hockey stick” has been pretty much discredited. That in fact there is compelling evidence for a “medieval warm period” and a “little ice age.” And that the “hockey stick” is the result of flawed analysis.

Cite?

[Reepicheep]

@Czarcasm

Cite?

Cite

Money quote “Overall, the committee believes that Mann’s assessments that the decade of the 1990s was the hottest decade of the millennium and that 1998 was the hottest year of the millennium cannot be supported by his analysis.”

[Czarcasm]

@Reepicheep

Cite

Money quote “Overall, the committee believes that Mann’s assessments that the decade of the 1990s was the hottest decade of the millennium and that 1998 was the hottest year of the millennium cannot be supported by his analysis.”

Rather than go by that one quote, I think I’ll read the whole article, including the discussion page. It looks like there is quite a bit of controversy when it comes to that entry.

[GIGObuster]

@Reepicheep

Cite

Money quote “Overall, the committee believes that Mann’s assessments that the decade of the 1990s was the hottest decade of the millennium and that 1998 was the hottest year of the millennium cannot be supported by his analysis.”

And I do remember that Mann was overall happy with the results of the committee.

The valid criticism is however a distraction of the main point: the hockey stick is still there. (think about it, where in a millennium graph you will find the 1930’s anomaly and the 90’s trend close by?) It is true that he was wrong with the year 1998, however the problem is and remains: he was not much out of the mark, the latest years do not show the temperature going down as what happened in the 30’s after that anomalous year. The last 10 years are still close to the mark. The hottest year of the 1930’s does not affect the reality that the hockey stick was not debunked.

http://environment.newscientist.com/channel/earth/climate-change/dn11646

Since 2001, there have been repeated claims that the reconstruction is at best seriously flawed and at worst a fraud, no more than an artifact of the statistical methods used to create it (see The great hockey stick debate).

Details of the claims and counterclaims involve lengthy and arcane statistical arguments, so let’s skip straight to the 2006 report of the US National Academy of Science (pdf). The academy was asked by Congress to assess the validity of temperature reconstructions, including the hockey stick.

“Array of evidence”
The report states: “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 1000 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”.

Most researchers would agree that while the original hockey stick can – and has – been improved in a number of ways, it was not far off the mark. Most later temperature reconstructions fall within the error bars of the original hockey stick. Some show far more variability leading up to the 20th century than the hockey stick, but none suggest that it has been warmer at any time in the past 1000 years than in the last part of the 20th century.

The main reason to me why one should not jump on the idea that the “hokey stick” was debunked is that there are more doubts on how the critics got their “debunking”.

RealClimate: The weirdest millennium

But Beck did not stop at simply using this outdated curve, he modified it as highlighted in green in Figure 2. First, he added a wrong temperature scale – the tick marks in the old IPCC report represent 1 ºC, so Beck’s claimed range of 5 ºC exaggerates the past temperature variations by more than a factor of three. Second, the original curve only goes up to the 1970’s. Since then, Northern Hemisphere temperatures have increased by about 0.6 ºC and those in central England even more – so whatever you take this curve for, if it were continued to present, the current temperature would be above the Medieval level, as in the proper reconstructions available today. As this would destroy his message, Beck applied another fakery: he extended the curve flat up to the year 2000, thereby denying the measured warming since the 1970s. With this trick, his curve looks as if it was warmer in Medieval times than now.

When approached directly about these issues, Beck published a modified curve on a website. He changed the temperature range from 5 ºC to 4.5 ºC – but he shortened the arrow as well, so this was just cosmetics. He also added instrumental temperatures for the 20th Century at the end – but with his wrong temperature scale, they are completely out of proportion. (In fact his version suggests temperatures have warmed by 2 ºC since 1900, more than twice of what is actually observed!)

Beck goes even further: in a recent article (in German), he has the audacity to claim that his manipulated curve is right and the more recent scientific results shown by IPCC are wrong. And for years, he has offered his curve on an internet site (biokurs.de) that distributes teaching materials for schools, with support from German school authorities. It is quite likely that his fake curve has been shown (and will continue to be shown) to many school children.

It is not true at all to say that the “hockey stick” was debunked, it is more accurate to say it was criticized, confirmed, corrected and still being discussed. (The hokey stick is really not much evidence, but a graphical representation of the evidence.)

[jshore]

@GIGObuster

The valid criticism is however a distraction of the main point: the hockey stick is still there. (think about it, where in a millennium graph you will find the 1930’s anomaly and the 90’s trend close by?) It is true that he was wrong with the year 1998, however the problem is and remains: he was not much out of the mark, the latest years do not show the temperature going down as what happened in the 30’s after that anomalous year. The last 10 years are still close to the mark. The hottest year of the 1930’s does not affect the reality that the hockey stick was not debunked.

Actually, GIGObuster, I think you are mixing up two things here. The hottest year being in the 1930s is a statement about the temperature record for the U.S. only and, it being a small percentage of the globe and the difference between it and 1998 being so small, it has little significance. On a global scale, 1998 (or 2005 depending on which data set you look at) is still the warmest year in the recorded temperature record…and the years in the 1930s aren’t even close. (See, for example, here.)

[1010011010]

Anybody got a graph of oceanic pH?

[jshore]

@brazil84

We’ve all heard of the infamous “hockey stick” graph that showed little temperature change from years 1000 to 1900; followed by a sharp rise between 1900 and 2000.

I had been under the impression that the “hockey stick” has been pretty much discredited. That in fact there is compelling evidence for a “medieval warm period” and a “little ice age.” And that the “hockey stick” is the result of flawed analysis.

You can read the NAS report on the subject online here. They did not “discredit” that work. They did feel that some of the findings (e.g., for temperatures going back more than 400 years) had large uncertainties (feeling that the Mann et al. work may have underestimated the uncertainties somewhat), so they did not feel that they could assign as high confidence to the claim that the latter half of the 20th century was warmer than any time in the last 1000 years as Mann et al. did. (In fact, they didn’t try to give any quantitative measure of their confidence in this conclusion.) However, they did note that all the reconstructions since that time have shown this to be the case. See the various reconstructions here. As you can see, by the way, the hockey stick graph certainly showed a Little Ice Age and a fairly modest Medieval warm period, although it is certainly not as pronounced as other some of the other reconstructions show.

If you look at the latest IPCC report out this year (see, e.g., the summary for policymakers), they state:

Average Northern Hemisphere temperatures during the second half of the 20th century were very likely higher than during any other 50-year period in the last 500 years and likely the highest in at least the past 1,300 years. Some recent studies indicate greater variability in Northern Hemisphere temperatures than suggested in the TAR, particularly finding that cooler periods existed in the 12th to 14th, 17th and 19th centuries. Warmer periods prior to the 20th century are within the uncertainty range given in the TAR.

Note that “very likely” means greater than 90% confidence and “likely” means greater than 66% confidence in the conclusion. So, they essentially re-affirm the conclusion about temperatures in the latter half of the twentienth century compared to those over the last millenium (actually now saying back 1300 years), and with the same confidence, as was stated in the TAR (the previous assessment report from 2001 where the hockey stick graph was prominently featured).

[jshore]

@1010011010

Anybody got a graph of oceanic pH?

Good question. I haven’t seen a graph and I am not sure how easy this would be to reconstruct. However, the oceans have indeed been acidifying as they absorb some of the CO2 we have put into the atmosphere…and this is a concern independent of the climate change effects of the CO2. (See this wikipedia article.)

[brazil84]

@jshore

You can read the NAS report on the subject online here.

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

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?

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?

[Czarcasm]

@brazil84

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

First, I found the following on one web site:

No, why don’t we stick to your own OP, or is this going to another thread where people respond to your thread topic by pointing out your mistakes, and you respond by ignoring what they post and just ask more questions?

[brazil84]

@Czarcasm

No, why don’t we stick to your own OP,

I’m a little confused. The “bristlecone” question is highly relevant to the “hockey stick” debate.

This is from the Wikipedia article on the hockey stick controversy:

Are bristlecone and foxtail pine tree rings valid temperature proxies?

Hockey stick graph (global temperature)

So I don’t understand why you think I’m not sticking to the OP.

Point of clarification: Are you making your comments as a moderator? Or as a regular poster?

[Czarcasm]

Unless I say differently, I am responding as a poster.
Do you have a response to what has been posted in reply to your OP, in particular the fact that the site didn’t exactly say what you claimed?

[brazil84]

@Czarcasm

Unless I say differently, I am responding as a poster.
Do you have a response to what has been posted in reply to your OP, in particular the fact that the site didn’t exactly say what you claimed?

Thank you. My exact claim was that I am under the impression that the “hockey stick” has been discredited; etc… Would you like me to link to a few articles that would give somebody such an impression?

[Czarcasm]

@brazil84

Thank you. My exact claim was that I am under the impression that the “hockey stick” has been discredited; etc… Would you like me to link to a few articles that would give somebody such an impression?

Since your first link failed in that aspect, sure.

[brazil84]

@Czarcasm

Since your first link failed in that aspect,

I haven’t linked to anything in this thread except the Wikipedia article, which I linked to for another purpose.

sure.

http://www.climate-skeptic.com/2007/09/chapter-4-skept.html

Under the “medium view” heading.

[brazil84]

@brazil84

I haven’t linked to anything in this thread except the Wikipedia article, which I linked to for another purpose.

http://www.climate-skeptic.com/2007/09/chapter-4-skept.html

Under the “medium view” heading.

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.

[Czarcasm]

@brazil84

I had been under the impression that the “hockey stick” has been pretty much discredited. That in fact there is compelling evidence for a “medieval warm period” and a “little ice age.” And that the “hockey stick” is the result of flawed analysis.

See this? This is the OP. Can you provide a link that supports your OP that the “hockey stick” has been pretty much discredited?

[LilShieste]

@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.

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

Once you answer that question, everyone can determine whether or not it’s worthwhile to even click on the link you provided.
LilShieste

[brazil84]

@Czarcasm

See this? This is the OP. Can you provide a link that supports your OP that the “hockey stick” has been pretty much discredited?

Please read my previous post. The link I gave gives the impression that the “hockey stick” has been discredited.