Michael Mann at UC Santa Cruz

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.


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.

Personal Comments

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.


  1. Jeremy
    Posted May 13, 2006 at 2:18 PM | Permalink

    Wow, so disagreement has absolutely no scientific basis. Where did these people learn science, in political science class?? People still question relativity for christs sake.

  2. nanny_govt_sucks
    Posted May 13, 2006 at 2:23 PM | Permalink

    He seemed a bit surprised and quickly responded that this was too technical of a point to discuss then and there,

    Reminds me of his response over at RC to my query about how the estimate of non-climate related effects to Bristlecone Pines was done in MBH99:


    [some non-specifics and misstatements about plant stomataes]… We’ll leave it at that.

  3. Posted May 13, 2006 at 2:40 PM | Permalink

    Dear Justin,

    thanks for your useful report. I’ve lived in Santa Cruz / UCSC for six months. The redwoods etc. are nice.

    Your summary is exactly what I expected: a boring, non-violent presentation of basic paradigms that avoids technical problems that are controversial. All tension going away during personal encounters. And a mild style of humiliating the skeptics which is accepted easily by the Santa Cruz hippies.

    A recommendation for the literature teacher who wants to fight against science as understood by the science department at her school: the best thing you can do for your climate political movement is to close your mouth because otherwise an increasing number of people will understand that the global warming hysteria is driven by irrational anti-scientific fiction readers who dislike their science-oriented colleagues.

    All the best

  4. Doug L
    Posted May 13, 2006 at 4:52 PM | Permalink

    [Triumphalism mode on]

    It would seem that they still feel these reconstructions are an important part of the propaganda effort. Mann really walks the walk (or is it skates the skate?):

    Live by the Hockey Stick, die by the Hockey Stick! 🙂

    Looks like we got a good outrageous statement– Mankind affecting climate in the stone age! [chuckle]

    Exxon-Mobil, hire this Justin fellow right away!

    [Triumphalism mode off]

    The R2 thing was good from a voyeuristic perspective but was doomed to be otherwise disappointing.

  5. fFreddy
    Posted May 13, 2006 at 6:52 PM | Permalink

    Finally, he rhetorically asked why would we totally disregard a model over one such small point.

    Ah yes, the “ignore the little man behind the curtain, I am the mighty Oz” defence.

    Thank you for this report, Justin.

  6. Pat Frank
    Posted May 13, 2006 at 8:03 PM | Permalink

    #4 “Looks like we got a good outrageous statement– Mankind affecting climate in the stone age! [chuckle]”

    Actually I’ve read about this possibility in another context. Michael Bird, an Australian scientist, wrote a paper about ancient use of fire as evidenced by carbon deposits in cores taken from south Atlantic bottoms. Fire was apparently extensively used world-wide to drive game before hunters and to modify woodlands to human benefit.

    Apprently from its start, the present interglacial has been much more arid and contains much more grassland than the previous ones; a condition thought due to ancient human burning of woodlands. There is speculation in that literature that ancient woodland burning was so wide-spread and so extensive that the airborne soot produced settled on polar ice and lowered its albedo enough to influence climate and perhaps bring the last glaciation to an earlier-than-otherwise end. That would have been a few decamillennia before cultivation, though.

    True or not about the last glacial end, I don’t know. I’ve not seen any quantitiative estimate. But it’s likely that ancient humans influenced climate by their use of fire.

  7. Posted May 13, 2006 at 8:37 PM | Permalink


    Thanks for the report. Did you record your conversations with Mann following the presentation? I would like to have an audio quote of his disregards for the most important questions about r2 to post on my blog.

  8. Geoff Smith
    Posted May 14, 2006 at 12:53 AM | Permalink

    #4, #6, and main thread:

    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.

    Looks like we got a good outrageous statement– Mankind affecting climate in the stone age! [chuckle]

    Actually there is a significant amount of serious literature on this topic. The “close friend” referred to by Mann is almost surely his old colleage at University of Virginia, William Ruddiman. He has a good overview of the hypothesis in his 2003 Climatic Change article “The Anthropogenic Greenhouse Era Began Thousands of Years Ago”.

    The abstract states: “The anthropogenic era is generally thought to have begun 150 to 200 years ago, when the industrial revolution began producing CO2 and CH4 at rates sufficient to alter their compositions in the atmosphere. A different hypothesis is posed here: anthropogenic emissions of these gases first altered atmospheric concentrations thousands of years ago. This hypothesis is based on three arguments. (1) Cyclic variations in CO2 and CH4 driven by Earth-orbital changes during the last 350,000 years predict decreases throughout the Holocene, but the CO2 trend began an anomalous increase 8000 years ago, and the CH4 trend did so 5000 years ago. (2) Published explanations for these mid- to late-Holocene gas increases based on natural forcing can be rejected based on paleoclimatic evidence. (3) A wide array of archeological, cultural, historical and geologic evidence points to viable explanations tied to anthropogenic changes resulting from early agriculture in Eurasia, including the start of forest clearance by 8000 years ago and of rice irrigation by 5000 years ago. In recent millennia, the estimated warming caused by these early gas emissions reached a global-mean value of àƒ⣃ ‹’€ à‚⺰.8 àƒ⣃¢’‚¬”à‚⥃ and roughly 2 àƒ⣃¢’‚¬”à‚⥃ at high latitudes, large enough to have stopped a glaciation of
    northeastern Canada predicted by two kinds of climatic models. CO2 oscillations of àƒ⣃ ‹’€ à‚⺱0 ppm in the last 1000 years are too large to be explained by external (solar-volcanic) forcing, but they can be
    explained by outbreaks of bubonic plague that caused historically documented farm abandonment in western Eurasia. Forest regrowth on abandoned farms sequestered enough carbon to account for the observed CO2 decreases. Plague-driven CO2 changes were also a significant causal factor in temperature changes during the Little Ice Age (1300–1900 AD)”.

    My amateur review is that he presently his case fairly, and discusses other hypotheses reasonably. I think he makes a pretty strong case that the CO2 levels over the past 8000 years are anomalous compared to prior interglacial periods.

    His chief explanation for this phenomena I find less credible at first glance. Ruddiman argues that land use changes (not the fires of cavemen), principally the clearning of forest for agricultural use, were the main cause of increased CO2. Although he proceeds very carefully to calculate the amount of decreased global biomass that would be necessary to lose the carbon sequestering ability that would permit an increase in total CO2 by 320 GtG, the main direct evidence is the Doomsday survey ordered by William the Conqueror in 1086 A.D., which reportedly found “less than 5% of the natural forest cover remaining over lowland regions, and less than 15% across the intire country (Rackam, 1980)”. Since Briton was a remote outpost of the Roman Empire by 2000 BP and largely deforested, Ruddiman believes it is reasonable that more heavily populated Europe and Asia would also have suffered the same fate.

    He then proceeds to show (with many references to literature) that deforestation was widespread globally, and calculates that this biomass reduction could explain 80% of the increased CO2 over the 8000 years prior to the industrial age.

    Without reviewing all the literature, I find it hard to accept that early man would take the effort to clear such wide areas of forest. Without chainsaws, it would be a lot of work. It’s also hard to see (and Ruddiman gives no explanation) of how early man could have deforested so large an area without effort.

    One more interesting point. Ruddiman argues that CO2 levels have declined in the three previous interglacials, and should have declined in the Holocene the same way. Therefore, the amount of extra CO2 to explain in the industrial period is not the 105 ppm usually referred to (current 385 ppm less the 1860’s 280 ppm or so), but actually 125 ppm, that is, the current 385 ppm less the level to which CO2 levels would have fallen in the pre-industrial era of about 240 ppm, if the pattern of the previous interglaciations would have held.

    From this, he presents the hypothesis that this pre-industrial anthropogenic effect is the “most likely reason” that another glaciation did not begin in northeast Canada several thousand years ago.

    The article is big fun, and seriously written. Looks like we may have to take some additional effort to emit more carbon to avoid another ice age.



    Ruddiman, W.F., The Anthropogenic Greenhouse Era Began Thousands of Years Ago, 2003, Climatic Change, volume 61, No. 3

    Rackam, O.,1980, Ancient Woodlands, Edward Arnold, London

    The Ruddiman abstract can be found here

  9. Geoff Smith
    Posted May 14, 2006 at 1:08 AM | Permalink


    1. let me see, 385 less 240 is (drumroll) 145 ppm. No physics or statistics please.
    2. Of course, fire can clear trees, but it’s not that easy routinely clear large areas that way.
    3. The Ruddiman abstract is here

  10. John Lish
    Posted May 14, 2006 at 1:22 AM | Permalink

    #8 – Thanks Geoff for that. Interesting argument. However, I wouldn’t draw the conclusion that humanity “took control” of the climate. The question of how much anthropogenic influence is open to speculation. As for forest clearing, it would have been done using managed burning with specific firebreaks IIRC.

  11. Geoff Smith
    Posted May 14, 2006 at 3:23 AM | Permalink


    Thanks John Lish, I’m also not convinced by the arguments (yet). I understand it’s easy to set fires in the summer if it doesn’t rain (like California) but more difficult where it rains year round.

    The hubris issue also sometimes comes to my mind: If some people think we know how to control the climate, shouldn’t they be advocating making the climate perfect? Who would like to volunteer for that job?

  12. BradH
    Posted May 14, 2006 at 5:21 AM | Permalink

    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.

    Hmmm…Of course whether trees are a proxy for temperature (and to within less than 0.5 degrees, back to 1400, no less) is thoroughly debunked!

  13. BradH
    Posted May 14, 2006 at 5:45 AM | Permalink

    The Antarctic ice is definitely shrinking since 2002 at least…

    Interesting you should say that, Steve, seeing as Justin reports Mann as saying:-

    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.

    Steve Bloom: Satellite Data Conclusively Proves Antarctica Is Melting

    Michael Mann: Skeptics’ Only Point – Satellite Data Dodgy

  14. Doug L
    Posted May 14, 2006 at 6:27 AM | Permalink

    If the effect of Mankind on climate in the Stone Age is significant, then we are all DOOMED! DOOMED!

    That is the subtext of the message, hence it is outrageous in the context of using these reconstructions as propaganda. Confusing too, since the climate was supposedly stable until recently.

  15. John Lish
    Posted May 14, 2006 at 7:10 AM | Permalink

    #13 controlling the climate? That came up on Prometheus a little while back – the question was who would have control of the thermostat? With every adjustment, there would be winners and losers so it could be another source of international disputes if feasibly possible.

  16. Steve McIntyre
    Posted May 14, 2006 at 8:11 AM | Permalink

    #8,9. Forests in Ontario were cleared for farms in the 19th century with back-breaking labor, oxen were important. My grandfather was born on a farm in Ayr, Ontario in 1890 and his father and grandfather spent much of their lives clearing land. He lived to be 94 and the recollection of the land clearing process becomes part of our family’s oral history, I guess. Human effort over time can do a lot even without chain saws. This is tangential to the Ruddiman position, just local color.

  17. John A
    Posted May 14, 2006 at 8:22 AM | Permalink

    Can anyone reconcile these two statements made by Michael Mann?

    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.

    -Michael Mann, Scientific American 2005

    He [Mann] 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.

    -Michael Mann, UCSC, 10 May 2006

    …because I can’t. If the Little Ice Age and the subsequent recovery to 1940 were solar forced, how could they be regional and not global phenomena?

  18. Steve McIntyre
    Posted May 14, 2006 at 8:37 AM | Permalink

    Justin reported that Mann asked:

    Finally, he[Mann] rhetorically asked why would we totally disregard a model over one such small point.

    One answer is this: IPCC TAR made the following specific statement about the MBH reconstruction – that it had

    “significant skill in independent cross-validation tests”.

    So this “small point” was what IPCC chose to highlight about the MBH model. Not entirely a “small point”.

    Wahl and Ammann hardly “disprove” ouir claims. Their supplementary table confirms our claims that MBH fails verification r2 and CE tests. Their argument is that this failure doesn’t “matter” on the basis that verification r2 and CE may reject a reconstruction with valid low-frequency properties through high-frequency tests.

    This is not a “disproof” of our claim that MBH failed standard cross-validation tests. Instead, they are trying to argue that the standard cross-validation tests aren’t valid. This is a much weaker position than originally advocated in MBH98. Had a position like this been clearly articulated in MBH98 i.e. the reconstruction fails cerification r2, but this doesn’t “matter” – then people at the time might not have put so much credence in MBH98. Now people are locked into positions and they are hard to move.

  19. beng
    Posted May 14, 2006 at 8:50 AM | Permalink

    RE #8

    Geoff, look at this pdf titled “The Holocene CO2 Rise:
    Anthropogenic or Natural?”:

    Click to access broecker06eos.pdf

    An interesting rebuttal of Ruddiman, I think.

  20. Posted May 14, 2006 at 9:07 AM | Permalink

    With respect to the early rise of CO2, the termite and ant family, thriving since the end of the last ice age, emit surprizingly large amounts of GHGs. Also, recently read a report about underground coal fires in China alone producing CO2 equivalent to US transportation. Many of those fires started in outcroping of coal seams exposed to forest and other fires. Clearly much CO2 rise after the last ice age comes from “natural” sources little studied.

  21. Brooks Hurd
    Posted May 14, 2006 at 10:35 AM | Permalink

    One issue which needs a lot more study before we have a reasonable answer is the percentage of climate change which is attributable to anthropogenic sources. Many in the cheering choir at RC believe that this percentage is close to 100%. The same can be said for many of the government ministers who created the Kyoto treaty. I doubt that either Mann or Ruddiman would claim that it is 100%, although Mann might claim that it is closer to 90% than to 10%. It is quite likely that the high school literature teacher who Justin described is convinced that this percentage is nearly 100%. All of these are assumptions.

  22. Posted May 14, 2006 at 10:44 AM | Permalink

    Dear John A,

    the reconciliation is easy. Consensus scientists believe that there are different Suns above different regions of the world. Some of these Suns recommended their people to burn witches and skeptics, and some of them did not. This got translated to different mini ice ages and mini climate optima via the enhanced greenhouse effect.

    All the best

  23. Tom Brogle
    Posted May 14, 2006 at 11:00 AM | Permalink

    In an email discussion with William M Connolley I put this comment to him.
    “The”raw” data in IPCCTAR does not
    correspond with “raw” data published by
    Parker in 1985.”
    (the 1985 data shows no overall rise in temperature whereas the IPCC does)
    I received no reply
    There is quite a good logical argument to demonstrate that the method used by GISS to correct for Urban Heat cannot do so.
    No one at GISS is prepared to discuss it.
    Finally the Jones data set shows that the Arctic temperature was as warm in the late 30s and early 40s as in the 90s. (I suppose that this data is largely uncontaminated with urban heat)

  24. Posted May 14, 2006 at 1:20 PM | Permalink

    RE #11


    There has been quite a bit of controversy over the last 4 years regarding mass loss of the Antarctic ice sheet, as a 2002 report stated that is was increasing.

    I brought this up on RealClimate, and the response I got from one of the authors was that it is well known that global warming will cause some near-edge melting, but that the increase in moisture would result in an increase in interior ice mass. Moreover, the author said the “moisture” factor is now dominating, so we are seeing an overall increase.

    So which is it? If the ice mass is melting, then their climate models must be wrong…

  25. Follow the Money
    Posted May 14, 2006 at 4:14 PM | Permalink

    Could you double-roger this – Did he say the cooling trend 1940-1970 was caused by “aerosols?”


  26. Posted May 14, 2006 at 11:21 PM | Permalink

    re #27

    It’s what I’ve got in my notes. Once I get the audio recording cleaned up and a chance to go through it, I will verify.

    On that point, anyone know if voice recognition software would do a decent job of transcribing the audio?

  27. Tom Brogle
    Posted May 15, 2006 at 3:38 AM | Permalink

    Steve Bloom
    Logically,if more ice is formed on the Antarctic plateau,more ice will melt at the edges of the of the continent.This is probably true for Greenland as well.
    If this did not occur, all the sea would have been turned to ice long ago .Thus increased melting at the from the edges of an ice cap is no cause for alarm especially when most of evidence indicates that such ice caps are thickening.

  28. John Hekman
    Posted May 15, 2006 at 4:58 PM | Permalink

    I don’t know if anyone here can help, but to frame the debate over AGW, I need a couple of basic questions on the “skeptic” side, so that when someone drags out the latest Al Gore talking points, I can show that there is a real debate by sayng, e.g., 80% of the world’s ice is located in Antartica, and while there is more melting at the edges, the temp has fallen recently in Antartica and the ice level is rising. Also I think Greenland has another 10% or so of the world’s ice, and the same two effects are occurring there.

    Anyone have a good suggestion? Thanks

  29. ET SidViscous
    Posted May 15, 2006 at 5:27 PM | Permalink

    Can’t help you on Ice.

    But my perrenial questions are.

    A. how much do you think the temprature went up over the 20th century?

    B. Do you think that is signifigant?

    C. Given that the climate HAS TO change, how much of a change do you considerable acceptable over 100 years.

  30. Steve Bloom
    Posted May 15, 2006 at 7:07 PM | Permalink

    Re #32: The difficulty is that it isn’t especially good news that they’re getting thicker in the center (due to the increased moisture capacity of the warmer air) while losing nass overall due to a much more rapid rate of loss at the edges. One thing we know about ice sheets is that they are capable of relatively rapid collapse; i.e., edge loss can be vastly greater than the increase at the center. You should read the papers, though (or at least the abstracts). Most of the current stuff is linked in the recent RC articles.

    Re #33: Read those papers! BTW, I think the latest is that the troposphere over Antarctica is indeed warming, although surface temps remain lower. There’s not a debate about the ice caps so much as a lot of people working on improving the measurements. New stuff seems to be coming out every month or two. As you will see discussed over at RC, the really big gap in the current science is the lack of an adequate model for dynamical ice loss. This lack exists because it wasn’t until the last few years that anybody had any idea that the ice could move so quickly. The Larsen B collapse was the wake-up call.

  31. Steve Bloom
    Posted May 15, 2006 at 9:00 PM | Permalink

    Speaking of ice, here’s a shorter-term concern: http://www.guardian.co.uk/science/story/0,,1774815,00.html . There’s considerable uncertainty about the extent and implicatins of the positive warming feedback that would result from the loss of the Arctic ice, but it clearly won’t be good.

  32. Charles
    Posted May 18, 2006 at 8:39 AM | Permalink

    I have yet to see an analysis regarding the pro and con of the expected moderate warming. Since almost all of the past and expected warming is concentrated in the higher latitudes, in the winter and at night there should be a net increase in growing season thus food production world wide.

    The only plausible negative I have heard of is a modest increase in ocean levels (~8inches) over the next 100yrs.

    Where’s the beef? The modest warming of the past 100yrs has been a net plus and there is no reason to believe modest warming over the next 100yrs will be any different.

  33. Brooks Hurd
    Posted May 18, 2006 at 10:51 AM | Permalink

    Charles, the issue is, if you believe the Mannian hockey stick reconstruction with Jones “instrument” records pinned to them, then it appears that we are now at a maximum as far as temperature is concerned. Mann has stated that he does not approve of overlaying his recon with instrument data, but I have not heard him upbraiding the IPCC for doing just that.

    150 years ago, we were at the end of the LIA, which clearly was a period of minimum temperature. Proxy recons which go further back (2,000; 5,000; 10,000 BYP or further) show much warmer periods which preceeded the LIA. Many of these longer proxy recons show that current temperatures (even Dr. Jones’ 2005 temps) are considerably cooler than several maxima over the past 5,000 years. This is clearly shown in at least one graph in the 4AR 2nd order draft, which I shall not quote or cite.

    In addition to your question about the effect of moderate warming, I would add the following: Our temperatures are warming from a recent temperature minimum. Natural systems are known to cycle betweeen minima and maxima. The temperature has changed significantly from the mid glacial minimum to the inter-glacial maximum. Humans have lived through a number of ice ages as well as much warmer (then today) interglacial periods. Why is it so unprecedented for the temperature to be recovering from a minimum?

  34. Michael Jankowski
    Posted May 18, 2006 at 11:35 AM | Permalink

    I have yet to see an analysis regarding the pro and con of the expected moderate warming.

    There are models out there to give you any con you want in the moderately warming future – summers too hot or too cold, winters too cold or too warm, more droughts and/or more floods, etc. And then there’s the more frequent and more intense hurricanes, spread of disease, etc. Anything “extreme” is an expected con. Basically, everything bad in your life will get worse with warming, and everything good in your life will disappear. At least, that’s what people are trying to lead me to believe!

  35. kim
    Posted May 21, 2006 at 1:26 PM | Permalink

    The latest word from a hot Oxford computer climate modeling scientist is “I don’t know Mann at all”. I take that as a bellweather of his fate.

  36. Hank Roberts
    Posted Oct 14, 2006 at 10:39 PM | Permalink

    Aerosols, warming, 1940-1970, Google Scholar:


  37. mccall
    Posted Nov 11, 2007 at 1:51 AM | Permalink

    I got here reviewing Wahl & Ammann stuff… missed catching this in May.

    re: 13 Velicogna’06 Antarctic Ice Mass shrink … this came from VP Gore and was parroted by Mr. Bloom?

    Velicogna’06 did show shrink that was due to the smaller West Antarctic Ice Sheet mass dominated over a short study period of a whopping 3+ years. Climatically, this is a joke that will likely be punch-lined when the analysis of the ’07 winter comes in — you know, the one with record ice area as of 26-SEP-07 (The Cryosphere Today)?

    (Like Keigwin’s Sargasso & forams) I’ve been through this one in other discussions; and it’s a yet another cherry-pick. Davis ’05 showed net Antarctic growth over a longer period from 1993-2003 — the end year overlaps the start of Velicogna’s 3+ years of short term decline. There are also other ’06 published studies that show growth: Chen et al.; Ramillien et al.; and van de Berg et al. Antarctica is ~2X the continental U.S. in area — and to paraphrase a popular tourism campaign, “what happens in the East Antarctic Ice Sheet, dominates Antarctica!”

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