2012-02-08 06:38:11Error in MWP rebuttal
John Cook


Someone emailed me this critique of our MWP intermediate rebuttal:

I would like to point out an error in your "How does the Medieval Warm Period compare to current global temperatures?"

Other commentators have alluded to this in the past.  In your intermediate section writeup, you show Mann's chart of the Medieval Warm Period, or as he calls it "the Medieval Climate Anomaly."  This chart shows years 950 - 1250.  But in your same writeup, you include your own graph of 1999 - 2008 as a comparison.  This is is hardly a fair comparison.  You are comparing data from the beginning to the end of the MWP to the warmest decade of our current history?  Even Mann makes no such comparisons in his paper.

You know, that's not an unfair criticism. Is comparing a 300 year period with a decade a fair comparison? On the other hand, hockey stick graphs are essentially a visual comparison of any instant in time with the entire period previous so they implicitly make the same comparison. Thoughts?

2012-02-08 12:30:39
Rob Painting

I'm assuming it's this poster jzk. This is how I replied.

"jzk - yes it would be neat if we had a whole bunch of global proxy data with sufficient resolution (detail), say at the annual (yearly) scale, but AFAIK there's not a great deal - and we know how worked up the fake-skeptics get about the tree-ring data.

You just have to work with what you have.

The real dagger to the heart of the MWP (to my mind) is the global circulations. Mann's reconstruction agrees very well with how we expect the circulations, and their teleconnections to operate. Not perfectly of course, but a warm MWP wouldn't agree at all.

For instance ENSO (La Nina/El Nino) was weaker (lower amplitude) then, and the natural oscillation in ENSO was longer (around 80 years?). This is consistent with a cooler tropical Pacific than today.

Additionally, the Amazon rainforest was wet - consistent with a more southward displacement of the ITCZ (inter tropical convergence zone) than exists today. Again suggesting a cooler global climate back in medieval times."

2012-02-08 20:38:11Comment
Robert Way


For me it is a fair point that he's brought up. comparing the warmest decade in the MWP to the warmest in the current period would be more appropriate. I personally think we have to redo a lot of our rebuttals to reflect up to date values and new studies...

2012-02-08 20:50:53Updating rebuttals
John Cook

For sure we need to update many rebuttals. We also need many more hours in the day!
2012-02-09 13:59:22We definitely need to update the MWP intermediate argument as a matter of priority.
Tom Curtis


My reasons are given here and here.


As an intermediate step, I recomend the final sentence be altered to read:


"What is more, and as can be seen below, globally, temperatures during the Medieval Period were less than today."

 and the following image (or some other suitable global reconstruction) be added below:


2012-02-09 14:12:47Tom, why not have a crack at it
John Cook


Rewrite the rebuttal, post it in the appropriate forum (Eg - basic rebuttals or intermediate rebuttals) and then when green thumbed, update the rebuttal directly yourself, being sure to archive the previous version.

2012-02-09 15:04:20
Tom Curtis


John, happy to do that when I get some time (about three weeks).  But as this is an actual error of argument, not an update or improvement in style.  By not correcting it, we may unintentionally mislead people, so an interim edit should be implemented immediately, which I do not know how to do (and do not think I am authorized to do).  I did not want to just say this should be done, and leave it in the hands of others, so I have made my suggestions for that edit so that if you or Dana agree it can be implimented immediately.  

2012-02-09 16:03:05
Dana Nuccitelli

What's the source of that figure Tom?

2012-02-09 16:58:05Dana
Tom Curtis


Mann et al, 2008  Supplementary material Figure S6


2012-02-19 08:04:45Comment
Robert Way


Watch out... doesn't validate before 1200...