the Air Vent

Because the world needs another opinion

Mann Discovers MWP

Posted by Jeff Id on August 13, 2009

I received an emial from someone whom deserves a hat tip for bringing my attention to the latest Mann paper.  Of course it was by email so I’m hesitant to say whom but thanks anyway.  He linked to an article in Science Now describing Mann’s latest hurricane reconstruction by proxy  and made the point that the MWP apparently does exist and what’s more, the hurricanes were as bad as the past decade.

Of course I’m skeptical, it’s Michael Mann and as someone pointed out last night, scientists have well earned reputations.  Still, let’s not make any claims which are unsupported by the data (or I’ll snip em — hehe).  RC contributor Dean was right on the other thread and the dogs got carried away.  We can leave any criticism on detail we don’t actually know alone.

Don’t worry though, I have a great deal of confidence we will find some magic in this paper.  I say that because it’s another proxy paper which means it will have the same sorting calibration issues never yet solved and regularly ignored in paleoclimatology so its an easy assumption to doubt the signal is of correct scale, however that also is an unknown.

Here is the abstract from Nature:

Atlantic tropical cyclone activity, as measured by annual storm counts, reached anomalous levels over the past decade1. The short nature of the historical record and potential issues with its reliability in earlier decades, however, has prompted an ongoing debate regarding the reality and significance of the recent rise2, 3, 4, 5. Here we place recent activity in a longer-term context by comparing two independent estimates of tropical cyclone activity over the past 1,500 years. The first estimate is based on a composite of regional sedimentary evidence of landfalling hurricanes, while the second estimate uses a previously published statistical model of Atlantic tropical cyclone activity driven by proxy reconstructions of past climate changes. Both approaches yield consistent evidence of a peak in Atlantic tropical cyclone activity during medieval times (around ad 1000) followed by a subsequent lull in activity. The statistical model indicates that the medieval peak, which rivals or even exceeds (within uncertainties) recent levels of activity, results from the reinforcing effects of La-Niña-like climate conditions and relative tropical Atlantic warmth.

Mann 08 presented this for a northern hemisphere temperature reconstruction.

mann 09 recons full length

Mann 08 Recons, Click to expand

You have to wonder when only one of his reconstructions (EIV Land Only) crossed the zero line at any time prior to 1000 AD and all the rest are below, Where exactly is this tropical Atlantic warmth coming from?  After all the Land plus ocean seems to drag the curves down even further than the land only.

Also, I just can’t resist pointing out Mann’s claim:

annual storm counts, reached anomalous levels

Followed by:

has prompted an ongoing debate regarding the reality and significance of the recent rise

It’s a non-uniqe form of debate to make the assertion strongly followed by a soft rebuttal to acknowledge the other parties weaker yet reasonable position.  If the storm anomalies are with certainty anomalous, isn’t the discussion about the validity of the anomaly itself anomalous?

My friend who emailed sent a link to Science Now Daily news which offered a bit more detail to the above points.

Researchers examining ocean sediments have concluded that current climate conditions resemble those that led to peak Atlantic hurricane activity about 1000 years ago.

Check this out, there is some explanation of the source of the data.

For more than a decade, scientists have been trying to determine whether climate change is linked to intense storms, such as 2005’s Hurricane Katrina. Meteorologist Michael Mann of Pennsylvania State University, University Park, and colleagues attacked the question by turning to the past. They looked through drill cores from coastal waters for signs that sediments had been disturbed by major storms. Eight sites along the U.S. East Coast and Puerto Rico provided a reliable record of the number of significant hurricanes going back about 1500 years. Other climate data and models added clues to water temperatures and hurricane intensity.

I’m interested in getting a copy of this data.  It doesn’t seem possible that 8 cores could ascertain the number of hurricanes considering how widely they make landfall but perhaps it’s true.  I wonder what the cores contain that indicates hurricanes, it does seem plausible that sediments would have discernible records.

At the time, according to estimates constructed from other geologic data, Atlantic water temperatures were relatively warm, “though not as warm as today,” Mann says. And Pacific temperatures were relatively cool, thanks to La Nina events. Warmer Atlantic waters whip up more storms, but warmer Pacific temperatures tend to create stronger jet streams that break up those storms. So the twin conditions a millennium ago produced kind of a “Perfect Storm” for hurricanes, he explains.

The differential was there between the Pacific and Atlantic and that’s the similarity they discuss above.  I hear a little desperation in the comments from this scientist quoted in ScienceNow.   I believe warm weather will probably cause stronger storms by the way, it’s just that sometimes these scientists are too interested in the storms being ‘substantially’ more severe when the evidence doesn’t support it… yet.

Atmospheric scientist Kerry Emanuel of the Massachusetts Institute of Technology in Cambridge agrees. The paper “shows that hurricane activity is indeed quite sensitive to climate,” he says, and that global warming could have a dramatic impact on the severity of these storms in the future.

Of course this post wouldn’t be complete without a graph of hurricane activity.


Northern Hemisphere Hurricane Activity Courtesy CA - Click to expand

Here is a link to the Science Now article.

And of course Steve M has already read the paper and noticed what is apparently a complete and utter lack of detail More Check Kiting at Nature. By check kiting Steve is pointing out that the only reference to methods points to an as yet unpublished paper in Science.  I think Mann’s recent 2008 willingness to publish all the data and code may have evaporated but we’ll see over the next few days.

If anyone can email a copy of the paper’s full text, it would be much appreciated.


Here’s the global temperature from the original hockey stick which was apparently a MWP denier which I snagged from WUWT, Thanks Anthony.


He’s got a thread also running, LINK.  Although linking to WUWT is kind of like advertising for the super bowl.

10 Responses to “Mann Discovers MWP”

  1. Antonio San said

    “Atmospheric scientist Kerry Emanuel of the Massachusetts Institute of Technology in Cambridge agrees. The paper “shows that hurricane activity is indeed quite sensitive to climate,”

    Woaw, who would have thought? 😉


  3. Mark T said

    Um, they’re using landfall hurricane data for the reconstruction, but comparing that to total count for current data? If I’m not mistaken, there is no trend in the landfall counts for the past century, even using Curry’s methods.


  4. Antonio San said

    The key of the paper is using a statistical tool to coerce the sediment data into making the 1,000ad time becoming a hot bed of Hurricanes and therefore tie this with subsequent statistical models they developed.

    If anything a cursory visual inspection of the sediment data offered in Figure 1. -especially paying attention to the age uncertainty of events- shows mostly activity prior to 800ad on every site. Then a paucity from 900ad to the 1,800ad, except at the Massachussetts site.

    Therefore, it is likely that the magic was to overweight the Mass. site in the stats. Once this is done, there should be no problem comparing the so called “independent” datasets. Let’s not forget that the sites are all located in the same aerological domain…

    Moreover Mann’s understanding of cyclogenesis is somewhat simplistic: if hot SST were the governing factor then there would be virtually hurricanes every day…

    Yet on page 882, the third page of the paper, the authors are describing the true uncertainty affecting these geological sites, the possible confusion with monsoon storms and cite the Caribbean activity for good measure and yet conclude with the traditional “robust” this time minored by a “reasonably”…

    The conclusion fizzles out with “suggest”, “some degree of additional validation”…
    So from a geological viewpoint this paper is hardly hard rock evidence. I am sure the statisticians will have a field day.

  5. Jeff Id said

    Data and code are here.

    While I can’t verify completeness,I would like to add a thanks to Dr. Mann for providing both at time of publication.

  6. Billy said

    I’m admit I’m completely out of my depth when it come to most of the math and science surrounding the AGW debate. However, I am totally fascinated by it and I spend a lot of time at sites like this trying to absorb as much as I can.

    The one thing that always surprises me is the level of faith that paleoclimatologists are putting in proxies. I know many posters at this site and others have questioned the accuracy of proxies before. E.g. I’ve read various threads about the ‘divergence problem’ and the seemingly unscientific way that was brushed off. But mostly it seems like the bulk of the effort here is spent debunking the statistical methods people like Mann used to construct their composite time series. Which is fine. I’m just wondering if somebody could tell me how much effort really goes into testing the accuracy of these proxies. I mean if there’s no sound scientific basis for the proxies then all the rest is bunk no matter what methods they use, right?

    I mean like I said, I’m no scientist, so maybe I’m way off base here, but intuitively this all just seems wrong to me. It just seems like somewhere somebody got the idea that everything that ever happened is recorded with great accuracy somewhere in the geological record. We just need to come up with the right way to tease the data out. I mean, c’mon, the sedimentary record? Okay, maybe that will tell you something interesting, but as an accurate measure of storm activity going back a thousand years? Really?

  7. Mark T said

    I’m just wondering if somebody could tell me how much effort really goes into testing the accuracy of these proxies.

    Almost none. There was one study done in the 90s, one that was never finished, that had come to the conclusion that tree-rings have an upside down parabolic response to temperature, confirming, of course, claims by the likes of me that the response is non-linear. Botanists will tell you tree-rings don’t make good thermometers, they’re better rain guages.

    I mean if there’s no sound scientific basis for the proxies then all the rest is bunk no matter what methods they use, right?

    I think you have hit the proverbial nail on the head. Really, it comes down to dendroclimatologists making a claim that the proxies are suitable for temperature, then simply moving on as if the assumption is proof. That’s it… It makes me think of the “and then a miracle occurs” Far Side regarding E=mc^2.


  8. timetochooseagain said

    3-Yeah, there is no trend, but I’ve seen Curry and others hand-wave that some storms maybe got counted twice and blah blah blah.

    As I see it there are two problems with this study:

    1. He does not take into account the possibility of undercounts before systematic aircraft reconnaissance (1944) or satellites (TIROS up in 1960 or so, and more and better since then) eg:
    2. His findings are at variance with previous paleotempestology research:

    Besonen, M.R., et al., 2008. A 1,000-year, annually-resolved record of hurricane activity from Boston, Massachusetts, Geophysical Research Letters, 35, L14705, doi:10.1029/2008GL033950.

    Elsner, J.B., T.H. Jagger, and K.-B. Liu. 2008. Comparison of hurricane return levels using historical and geological records. Journal of Applied Meteorology and Climatology, 47, 368-374.

    Scileppi, E. and J.P. Donnelly. 2007. Sedimentary evidence of hurricane strikes in western Long Island, New York. Geochemistry, Geophysics, Geosystems, 8(6), 1-25.

    Nyberg, J., B.A. Malmgren, A.Winter, M.R. Jury, K.H. Kilbourne, and T.M. Quinn. 2007. Low Atlantic hurricane activity in the 1970s and 1980s compared to the past 270 years. Nature, 447, 698-702.

    Nott, J., J. Haig, H. Neil, and D. Gillieson. 2007. Greater frequency variability of landfalling tropical cyclones at centennial compared to seasonal and decadal scales. Earth and Planetary Science Letters, 255, 367–372.

    Donnelly, J.P., and J.D. Woodruff. 2007. Intense hurricane activity over the past 5,000 years controlled by El Niño and the West African monsoon. Nature, 447, 465-468.

    Miller, D.L., C.I. Mora, H.D. Grissino-Mayer, C.J. Mock, M.E. Uhle, and Z. Sharp, 2006. Tree-ring isotope records of tropical cyclone activity. Proceedings of the National Academy of Sciences, 103, 14,294-14,297.

    Here’s what Mann thinks of Landsea’s work:

    “Mann disputed Landsea’s research, saying that his technology argument ignores the chance that a single storm could have been counted twice before satellite records could show the exact track. He expressed doubt that the study would pass muster to be published.”

    OOPS. Guess there was a fluke. Seeing as it DID get published, see.

  9. Antonio San said

    “Mann … He expressed doubt that the study would pass muster to be published.”

    Indeed when obviously as someone said, the gate keepers keep the gate open for the right people…

  10. Mark T said

    I swear… he sits and speculates about what might have happened without ever offering a shred of evidence that it did happen. What a joke, anything to defend his castle.


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