Michael Mann knows his students and his subject. The topic of the graduate seminar: El Ni¿o and radiative forcing. The beer he will be serving: Corona, "because I'm going to be talking about tropical climate." Not surprisingly, attendance is high.

Mann is most famously known for the "hockey stick," a plot of the past millennium's temperature that shows the drastic influence of humans in the 20th century. Specifically, temperature remains essentially flat until about 1900, then shoots up, like the upturned blade of a hockey stick. The work was also the first to add error bars to the historical temperatures and allow for regional reconstructions of temperature.

That stick has become a focal point in the controversy surrounding climate change and what to do about it. Proponents see it as a clear indicator that humans are warming the globe; skeptics argue that the climate is undergoing a natural fluctuation not unlike those in eras past. But Mann has not been deterred by the attacks. "If we allowed that sort of thing to stop us from progressing in science, that would be a very frightening world," says the 39-year-old climatologist in his University of Virginia office overlooking the hills of Monticello, the home of Thomas Jefferson.

To construct the hockey-stick plot, Mann, Raymond S. Bradley of the University of Massachusetts Amherst and Malcolm K. Hughes of the University of Arizona analyzed paleoclimatic data sets such as those from tree rings, ice cores and coral, joining historical data with thermometer readings from the recent past. In 1998 they obtained a "reconstruction" of Northern Hemisphere temperatures going back 600 years; by the next year they had extended their analysis to the past 1,000 years. In 2003 Mann and Philip D. Jones of the University of East Anglia in England used a different method to extend results back 2,000 years.

In each case, the outcome was clear: global mean temperature began to rise dramatically in the early 20th century. That rise coincided with the unprecedented release of carbon dioxide and other heat-trapping gases into the earth's atmosphere, leading to the conclusion that industrial activity was boosting the world's mean temperature. Other researchers subsequently confirmed the plot.

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."

11 Comments

1. 1. Scott K. Smith 06:14 PM 3/15/08

   I would expect more from your magazine. This is trash, and I can prove it ! Mann is politically motivated and oblivious to his (and his friend's) many errors and biases. For an OBJECTIVE assesment of this idiot's "science" I would hope that readers would go to: http://www.john-daly.com/hockey/hockey.htm and read an honestly researched scientific paper (with more than enough footnotes to make it credible!). If you mind is already made up, I would strongly avoid your reading this. You will be SEVERELY embarrassed!

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2. 2. pjnevada 03:16 AM 6/8/08

   It seems to me that if the proxy method was used to estimate global temperatures prior to 1850, then the same methodology should have been used for post 1850. I wonder what changes would be apparent in the graph then?
   
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   Edited by pjnevada at 06/07/2008 8:45 PM

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3. 3. pjnevada 03:28 AM 6/8/08

   If Mann argues that the Medieval Warming Period and the Little Ice Age are simply regional phenomonon and not statistically relevant to Global Warming as a whole, then as a logical corollary, so called Global Warming science has no ability to predict or correlate to regional climates. Therefore, all the Chicken Littles out there would seem overwrought.
   
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   Edited by pjnevada at 06/07/2008 8:31 PM
   
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   Edited by pjnevada at 06/07/2008 8:47 PM
   
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   Edited by pjnevada at 06/07/2008 8:47 PM
   
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   Edited by pjnevada at 06/07/2008 8:48 PM

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4. 4. An Inquirer 01:37 PM 8/7/09

   This article is an embarassment to your magazine. The author would be better suited to be a PR manager for a political candiate than to be a journalist. The article extols Mr. Mann rather than examine the objections to his work. The problems are glossed over, and the reader gets the impression that they have been successfully addressed. I have studied the problems, and they are far from being addressed. In fact, if a university student of mine had tried the to handle issues like Mr. Mann did, he would not have received a passing grade. There is something seriously amiss in the academic and journalistic worlds when somebody gets free passes because he or she adheres to a popular political belief.

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5. 5. floyd 08:11 PM 9/7/09

   Climate change denialists have yet to produce a single shred of credible evidence to support their bizarre claim that anthropogenic climate change is a vast conspiracy perpetrated by >90% of professional climatologists and every single scientific organization of note in the world (e.g., all of the National Academies of Science, the American Geophysical Union, the American Institute of Physics, the National Center for Atmospheric Research, the American Meteorological Society, ...). All you need to do, denialists, is produce a scientific paper that can actually survive a rigorous peer-review and be published in a reputable scientific journal and your views, politically motivated though they are, will suddenly acquire much more credibility. Until then, you deserve to be considered little more than wild-eyed conspiracy theorists of the same ilk as those who believe the U.S. Government staged the 9/11 attacks.

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6. 6. VG 09:42 PM 10/6/09

   In light of recent findings concerning BRiffa et al. I would never submit any work for publication in your journal until you seriously reconsider your policy of making ALL raw data available for independent analysis when requested to do so. It is a scandal that you have not formally withdrawn this work in the light of recent events concerning BRiffa's work.

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7. 7. VangelV 09:45 PM 1/10/10

   Why would your magazine risk ridicule by putting out this type of trash given what we know about the Hockey Stick investigation by the Wegman Committee, Mann's unethical behaviour, and his likely academic fraud? I would expect a great deal more from a magazine that I used to read regularly and trusted.

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8. 8. VangelV in reply to floyd 09:48 PM 1/10/10

   It seems to me Floyd that you have it backwards. It is the AGW movement that has yet to produce a single shred of credible evidence to support their bizarre claim that human CO2 emissions are responsible for climate change. Show us one.
   
   Keep in mind that the sceptics can point to the ice core studies that show that the temperature trend changed first and that CO2 concentrations followed. That makes CO2 the effect, not the cause.

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9. 9. fuddydud 09:06 AM 5/23/10

   Perhaps AGW advocates would consider reading Iam Plimer's essay: " Heaven and Earth" and viewing the DVD documentary " The Great Global Warming Swindle"

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10. 10. jct405 02:04 PM 2/18/12

    I am new to SA. After just now reading the Mann interview Mar 2012 I logged in expecting to see scientists agreeing on science. Wow! Looks like a lot of really thoughtful, smart people are not agreed on the science. Is this a consequence of politics and egos (both sides)? Or a consequence of a valid 'more research is necessary' claim?

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11. 11. freddyv 08:15 PM 1/19/13

    I spend a lot of time researching climate change and while it is clear that it, and the increase in co2, is something we should be concerned about, it is equally clear that Mann has played fast and loose with the truth. That should not be allowed, but it seems to be very common in AGW circles...such a shame.

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