This is the eyewitness account by Justin Rietz of the talk given by Michael Mann at University of California at Santa Cruz on Wednesday 10th May 2006.
I made it down to Santa Cruz for the Mann presentation Wednesday night. I missed the first 10 to 15 minutes (those of you who live or have lived in the area know what rush hour traffic at 5:30pm is like on highway 17). I don’t think I missed much, as most of the presentation was intro level, i.e. "CO2 is a greenhouse gas, things like volcanoes produce C02 as does burning fossil fuels, the difference between the greenhouse affect and AGW, etc."
For those of you who are only interested in what Mann had to say about r2 calculations, skip down to the section labelled "MANN ON r2."
Disclaimer: In the main, this isn’t a Mann expose or op ed article on my part- I tried to objectively capture what was said based upon my notes, and so the text may be a little dry. I am sure my notes aren’t perfect, and I may may have missed some details or misstated exactly what was said. However, I have an audio recording to keep me honest (it isn’t great quality so I need to clean it up), and I will defer to it as the final word. At the end, I do take the liberty of including some personal thoughts to add a little "color."
Most, if not all of the graphs in Mann’s Powerpoint were from the IPCC’s "Climate Change 2001: The Scientific Basis." He displayed the "Spaghetti" graph, commenting that most of the trend lines showed unprecedent temperature increase in the 20th century. He then stated that the reason for the variance between the trend lines was due to differences in exactly what was being measured in each study, i.e. annual data, seasonal data, etc.
He spoke about solar radiation, and stated that the "mini ice age" was a result of solar radiation changes, and that this data is available through tracking of sunspots, there being data going back to the early 17th century thanks to Galileo and his successors. Mann moved on to discussions about C02 with fairly elementary explanations of the greenhouse affect, not inappropriate given the audience. He stated that there is an equilibrium in which the earth "tries" to bounce back solar radition via infrared radiation. He also said that the early 20th century warming period was caused by changes in solar trends. He also mentioned that the late 20th century cooling was due to volcanic activity. Several times he pointed out that there are still areas of uncertainty and that further research needs to be done.
The next part of Mann’s presentation dealt with the current state of the climate and possible outcomes in the future. He claimed that the climate effects of El Nino and La Nina are indicative of what we can expect from global warming, but that we will see some effects similar to El Nino and some similar to La Nina. He then focused on the U.S. Southwest, where he believes global warming will cause a"La Nina" effect, with an increase in drought. He stated that this has added significance because this part of the U.S has a growing population and tight water supply. He projected with pictures of drought from the 1930s and 1990’s, both taken in Oklahoma, I believe. He also referenced research by Webster & Holland (sp?).
Mann made several comments regarding recent climate trends, saying something to the affect that 2005 was the biggest season for chaotic weather (my notes here are unclear). For evidence, he pointed to the first tropical storm in Europe and the frequency & size of recent hurricanes (I believe he said the most and largest in recorded history). While this may be due to chance, Mann said that this may also be indicative of global warming.
He finished his presentation by saying that recent temperatures are unprecedented in this century, and most likely in this millenium.
Q & A
I was in the back, having arrived late, and unfortunately no one outside of the first 3 or 4 rows had a chance to ask questions. However, I did wait around afterwards and was able to talk to Mann directly (see "MANN ON r2" below).
A range of questions were asked, some that would be described as one-sided, softball questions, but others that were relatively objective, science-based.
One person asked what he (Mann) thought are the strongest arguments of the skeptic crowd. Mann first said the questions regarding the validity of satellite data. He then pointed out that one of the research papers regarding this topic had an algebraic flaw regarding sine, stating this as evidence that the sceptics’ results were inaccurate (no name mentioned). He then said that more recent research deals with this issue. His second point was regarding urban heat islands. Mann said these claims had also been discredited – if you throw out all temperature measurements from urban areas, or only use ocean temperature data, you end up with the same results.
Mann also stated that the cooling trend from 1940-1970 was caused by the release of aerosols into the atmosphere.
Another audience member pointed out the melting polar ice caps, to which Mann nodded in agreement. He then spoke about Greenland and the affects that melting there could have on ocean levels.
Several questions were raised regarding the possibility of another mini ice age or full-on ice age, at which point he discussed a theory regarding the possible affects of fresh water from melted ice caps on ocean temperature and currents. He pointed the audience to an article by Bryden (sp?) in Nature. In regards to a question about whether or not the recent warming trends are truly unprecedented given the warming that occured at the end of the last ice age, Mann discussed research by a "close friend" that theorized that human cultivation patterns thousands of years ago may have had an impact on the climate and speeded the end of the last ice age. He then stated that if this is true, humans "took control" of the climate thousands of years ago.
MANN ON r2
Afterwards, I chatted with Mann and several other people on a couple of different topics, mostly regarding how primary schools should teach science in regards to global warming. A literature teacher expressed her concern that the science department head at her school is absolutely convinced that AGW is more or less baseless, and that he teaches this to the students. She then asked Mann for recommendations on how she might handle the situation (she subscribes to the AGW position). Mann first stated that her situation is similar to the debate regarding teaching evolution: one side has facts on its side (evolution theorists and AGW), and the other side has "absolutely no scientific basis" (I believe these were his exact words). He then stated that he didn’t know of a single science textbook on the subject that disregarded AGW, and suggested she provide several sample textbooks to her school’s principal. For my part, I said I understood her situation and suggested she hold a school symposium where each side could provide their evidence in a structured debate and let the students decide for themselves.
I then introduced myself to Mann and said that I follow both RealClimate and ClimateAudit. I asked him if he would put to rest for me my concerns about his calculations of r2 in MBH98, not providing the results of these calculations, and whether or not the r2 results were significant. I said this in a friendly, non-aggressive manner, fitting the general tone of the discussions.
He shook his head and slightly chuckled, and responded that yes, this is an ongoing debate. He said there were several individuals involved in this debate, and he somewhat off-handedly mentioned Steve McIntyre and Ross McKitrick. He continued by saying that one is an economist and the other works for the mining industry, suggesting that their work should be taken with a grain of salt because of this, which caused an understanding chuckle among the group – except me, as my background is in economics. ;-) He continued by saying that a recent paper (Ammann and Wahl) goes through M&M’s points and dissproves each one. Finally, he rhetorically asked why would we totally disregard a model over one such small point.
I was a bit surprised by this last comment and said to him "From my understanding of statistics, isn’t r2 as a measure of correlation important when determining the validityof a regression model?". He seemed a bit surprised and quickly responded that this was too technical of a point to discuss then and there, and asked that I read Ammann and Wahl as the definitive answer to my question. At that point he turned away to speak to someone else.
At first, I found Mann’s presentation interesting and fairly objective as he was relatively clear about where uncertainties in climate research still exist. However, as the presentation continued, I noticed that he would subtlely include things that wwere clearly meant to subjectively sway the audience. The photos of the drought in Oklahoma were one example, others being the words and phrases he would use ("we may well have taken hold of the climate 1000’s of years ago"). He often would caveat his claims, but it was clear what he was suggesting.
Towards the end of his presentation and during the Q&A, I felt he pretty blatantly presented a one sided story – talking about the melting of ice caps and glaciers, but failing to mention that some recent studies show the Antarctic ice cap is growing; mentioning the in-progress research regarding the affect of human activity on the end of the last ice age; and suggesting that weather patterns in 2005 may well be proof that we are already experience global climate change due to human activity. I don’t remember him correcting or challenging any of the fairly far-out statements made by the infamous Santa Cruz types (though I would say, on the whole, the audience seemed quite balanced.)
In regards to my brief discussion with Mann afterwards, part of me expected to get a reasonable answer that would make me think "hmmmm, that seems legitimate, I guess all of the hype about r2 is just a red herring." However, his reaction when I questioned him about the importance of r2 for validating a regression model had the opposite effect. He didn’t show any signs of being frustrated or angry about having to deal with the topic again. Instead, I thought he was a bit surprised by my second question and really wasn’t confident about answering it. Just my opinion, of course.