Dr. Mann,

I’m sure that you are tired of revisiting your original “hockey stick” paper of a decade ago, but I do have a question (well, actually a few questions).

According to Steve McIntyre, the “short centered” PCA method you implemented can “mine” random noise for “hockey stick” shapes.

Well, I was able to replicate McIntye’s results with a SciLab script that I wrote.  When I generated a number of ensembles of “red noise” time-series and computed “short centered” principal components, the probability of obtaining a “hockey-stick-shaped” leading principal component was quite high. 

However, when I looked at the eigenvalue magnitudes of my “red noise hockey-sticks”, I noted that they were *much* smaller than the eigenvalue associated with your “hockey stick” leading principal component.  I was able to generate “hockey-stick” leading principal components with associated eigenvalue magnitudes of about 0.03 or so, an order of magnitude smaller than the eigenvalue associated with your “hockey stick” leading principal component.

In fact, in order to capture a large fraction of the variance of the red noise, I would have had to include 30 or more “red noise” principal components in the regression step.  This is in contrast to the 3 or 4 (IIRC) eigenvalues needed to capture most of the variance in your own data.

So it appears to me that McIntyre’s exercise was more “red herring” than “red noise”.

So Dr. Mann, is my line of thinking correct here?  Did McIntyre effectively accuse you of using the PCA method to “cherry-pick” a tiny fraction of your data to fish out a “hockey stick”?

And wouldn’t a quick look at the eigenvalue spectrum of an ensemble of time-series pretty much guarantee that any competent analyst wouldn’t commit the blunder that McIntyre implied that you committed?  I mean, wouldn’t a nearly flat eigenvalue spectrum tend to indicate that there isn’t much of a “common temperature signal” to work with?

And if I am correct here and were trying to explain all this to a nontechnical person, would it be fair to say that while the leading principal component may define the “shape” of the hockey stick, its associated eigenvalue defines its “size”?

And would it also be fair to say that McIntyre generated a “tiny ” hockey stick from red noise that he then tried to equate with your “big” hockey stick?

Dr. Mann,

In a 2007 interview Dr. Nils-Axel Mörner accused the IPCC of fabricating sea-level rising data. In particular he said IPCC reports claimed rising sea-levels despite none of the report authors being sea-level specialists.

Do you stand by the IPCC’s claims on rising sea levels? If so, what evidence can you offer to refute Dr. Nils-Axel Mörner?

Do you believe there is a current trend of rising sea-levels? If so, on what data do you base this claim? If not, how do you reconcile the discrepancy between record global temperatures and unchanging sea-level observations?

http://www.21stcenturysciencetech.com/Articles 2007/MornerInterview.pdf

Perhaps these are tangential questions to a scientist, but I think they merit some consideration:

1. Generally speaking, I find that many more liberal outlets focus on the doomsday scenarios rather than how scientists arrive at their conclusions; cultural competitors often see this as evidence confirming that scientists are trying to scare the people at large into funding their research.  On the other end of the spectrum, you have media outlets that completely straw man the science and are more responsive to dissenters (no matter their background) than they are scientists.  Somewhere in the middle you have outlets that are so focused on presenting two sides to a story that they don’t proportion their presentation to the evidence.  What can climate scientists do to improve the representation of their field in the media?

2.  What are scientists doing, and what can we do, to divorce politics from science?  Of course scientific discoveries have political ramifications, but the preference to style in politics does serious damage to the climate science cause, where we hope substance would ultimately win out.  I think it has been damaging to climate science that the primary face of AGW in Western media has been Al Gore.

Dr Mann,
  What do you think will be the climate/weather story of 2010?  The amazing snows recently seem likely to win, but that may be just because of they are fresh in our minds.

Other questions people have raised sound great.

Three questions which are more background or perspective:

1. What is thought to have caused the temporary local warming which allowed the Vikings to colonize Greenland for a while—are there other examples like this that non-climatologists don’t know about…
2. Had the glaciers receded in Canada long before civilization began in Mesopotamia, or were they somewhat overlapping in time?
3. Was it really hotter at the time of the dinosaurs (etc.) and if so what is thought to be best explanation.

Maybe these don’t fit but thanks for opportunity to suggest questions.  I’m looking forward to the podcast.

Background

In September 2008, Dr. Mann’s group published an important paper on Earth’s temperature history for the past 2,000 years in the prominent peer-reviewed journal Proc. Natl. Acad. Sci. USA.  Temperature signals were extracted from many long-term data series, such as tree rings and ice cores.  The paper has been strongly criticized for its inclusion of the lakebed sediments characterized by Finnish geologist Mia Tiljander.  Critics claim that the four Tiljander proxies are uncalibratable due to contamination of the temperature signal by local activities, from the 1700s to the present.  Critics also claim that the PNAS paper mistakenly uses two of the Tiljander proxies in an upside-down orientation, such that “warmer” information is added to the paleotemperature reconstructions as “colder”, and vice versa.  In his Response published in PNAS in February 2009, Dr. Mann called these criticisms “bizarre,” but he did not explicitly rebut them.

Questions

1.  Can the four Tiljander proxies be calibrated to the instrumental temperature record that spans 1850 to 1995?

2.  Do the PNAS paper’s reconstructions use the temperature information in the “tiljander-2003-xraydenseave” and “tiljander-2003-lightsum” series in a manner that is consistent with the interpretation offered by Mia Tiljander in her 2003 paper?

My question is:

How are we going to remediate anthropogenic climate change if we do not reduce the world’s population?

Here are two questions I’d like Dr. Mann to discuss:

1. Recently, your colleague Dr. Phil Jones acknowledged in an interview (London Daily Mail, Feb. 14) that the Medieval Warm Period may have been as warm as, or warmer than, current temperatures. If this is correct, it follows that your famous “hockey stick” graph cannot be defended, as it shows current temperatures definitely warmer. Do you agree with Dr. Jones on this matter? Please explain why or why not.

2. In one of the so-called “ClimateGate” emails, Dr. Jones says that he had “just completed Mike’s [Dr. Mann’s] Nature Trick of adding in the real temps to each series for the last 20 years (i.e., from 1981 onwards) and from 1961 for Keith’s to hide the decline.”  Please explain the so-called “trick” that Dr. Jones says you used in Nature to “hide the decline” in temperatures. Do you feel that this is a proper statistical procedure?

Dr Mann,
  What are the key climate health indicators the public should watch?  Sea Level?  Arctic Sea Ice Extent?  Greenland Mass Loss?  GISS temperature data?  Drought levels?

Folks,
The interview with Michael Mann has now been recorded, and some of these questions were used. By all means the thread should continue…but I can’t use any more. Thanks for all of them!

chris

Well, folks, the show is now live.

http://www.pointofinquiry.org/michael_mann_unprecedented_attacks_on_climate_research/

I thank you all for contributing to it, but especially mckenzievmd and Pragmatic Naturalist, whose questions were used on the air—and produced great responses from the guest!

Let’s keep this tradition going

chris

“Perhaps if the “cap and trade” supertax agenda was not being so agressively purveyed as the sole and necessarily immediate cure to GW which MUST be controlled by what basically amounts to a non-elected world (and basically foreign) government, it could not then be accused of being just a massive power grab and/or wealth redistribution plot of the “new world order” as so many conspiracy theorists love to point out.”

If conservative continue to deny the problem instead of proposing conservative solutions, then the only viable solutions left will be liberal by default.

The only solution that will work is to decrease human population to a sustainable level. We have passed our planet’s carrying capacity, and all talk of climate change remediation is useless without planning peaceful ways to reduce our population.

DarronS - 01 March 2010 05:32 AM

The only solution that will work is to decrease human population to a sustainable level. We have passed our planet’s carrying capacity, and all talk of climate change remediation is useless without planning peaceful ways to reduce our population.

I sure would be great if you could convince Ratzinger with your arguement!