2010-08-15 17:52:56Medieval Warm Period was warmer
Robert Way

robert_way19@hotmail...
142.162.181.139
One of the most often cited arguments of those skeptical of global warming is that the Medieval Warm Period (800-1200 AD) was as warm as or warmer than today. Using this as proof to say that we cannot be causing current warming is a faulty notion based upon rhetoric rather than science. So what are the holes in this line of thinking?

Firstly, evidence suggests that the Medieval Warm Period was in fact warmer than today in many parts of the globe such as in the North Atlantic. This warming thereby allowed Vikings to travel further north than had been previously possible because of reductions in sea ice and land ice in the Arctic. However, evidence also suggests that some places were very much cooler than today including the tropical pacific. All in all, when the warm places are averaged out with the cool places, it becomes clear that the overall warmth was likely similar to early to mid 20th century warming. Since that early century warming, temperatures have risen well-beyond those achieved during the Medieval Warm Period across most of the Globe. This has been confirmed by the National Academy of Sciences Report on Climate Reconstructions. Further evidence (Figure 1) suggests that even in the Northern Hemisphere where the Medieval Warm Period was the most visible, temperatures are now beyond those experienced during Medieval times.

Secondly, the Medieval Warm Period has known causes which explain both the scale of the warmth and the pattern. It has now become clear to scientists that the Medieval Warm Period occurred during a time which had higher than average solar radiation and less volcanic activity (both resulting in warming). New evidence is also suggesting that changes in ocean circulation patterns played a very important role in bringing warmer seawater into the North Atlantic This explains much of the extraordinary warmth in that region. These causes of warming contrast significantly with today's warming, which we know cannot be caused by the same mechanisms.

Overall, our conclusions are:
a) Globally temperatures are warmer than they have been during the last 2000 years, and
b) the causes of Medieval warming are not the same as those causing late 20th century warming.


Figure 1: Northern Hemisphere Temperature Reconstruction by Moburg et al. (2005) shown in blue, Instrumental Temperatures from NASA shown in Red.
2010-08-15 18:24:03Reconstruction comment
Robert Way

robert_way19@hotmail...
142.162.181.139
Anyone wondering why I chose moburg (2005) for the reconstruction (and not Mann) should see
http://wattsupwiththat.com/2010/08/14/breaking-new-paper-makes-a-hockey-sticky-wicket-of-mann-et-al-99/#comment-457390
2010-08-16 09:25:26No commentary?
Robert Way

robert_way19@hotmail...
142.162.181.139
No commentary?
2010-08-16 10:18:29Re M&M 2010
doug_bostrom

dbostrom@clearwire...
184.77.83.151

Some problems w/that paper. A "smoking gun" that turns out to be a little less, possible a "gub." See comments on these threads:

http://julesandjames.blogspot.com/2010/08/once-more-into-breach.html

 

http://julesandjames.blogspot.com/2010/08/how-not-to-compare-models-to-data-part.html

 

Also see the politically freighted and extraordinarily baroque

 

http://wattsupwiththat.files.wordpress.com/2010/08/mcshane-and-wyner-2010.pdf

 which is in competition w/M&M 2010 at WUWT as the flavor of the day. 

 

What's sort of annoying about this is how WUWT et al leap into the fray -prior- to any reasoned comments from academics and the like or even waiting for publication for that matter.

2010-08-16 11:09:42Response to Doug
Robert Way

robert_way19@hotmail...
142.162.181.139
Either way i've seen some very strong evidence (colleague submitting a manuscript soon) that century scale variability is being missed out on by predominantly tree ring data. The evaluation of the different reconstructions comes up with moburg as being the one would catches centennial and decadal changes the best (that's why I used it).

I don't doubt the findings of the new paper but something is striking from the paper (Gavin pointed this out at RC), the paper states "If we consider rolling decades, 1997-2006 is the warmest on record; our model gives an 80% chance that it was the warmest in the past thousand years”

So even with their analysis their findings are consistent. Either way my second point in the post makes the first point irrelevant. Any thoughts on the blog post?


2010-08-16 15:58:48
gpwayne
Graham Wayne
graham@gpwayne...
81.152.239.255
Hi Robert - when you say "the Medieval Warm Period was as warm as/warmer than today and that this proves that we cannot be causing current warming", do you think it worth clarifying the issue by mentioning sensitivity and JC's take that the MWP actually demonstrates greater sensitivity?
2010-08-16 18:05:36
Anne-Marie Blackburn
Anne-Marie Blackburn
bioluminescence@hotmail.co...
80.42.219.219

I think it's a good effort, but I that the uncertainties need to be included in your conclusion.

As for including climate sensitivity, I'm not sure because it complicates matters and it might be one step too far for our target audience. I think that mentioning global temperatures and the causes of the MWP does the job for this post.

As an aside I have to agree with doug_bostrom - there are already questions being asked about the McShane and Wyver's paper which hasn't even been published yet. I certainly don't think it's reason enough to just discard Mann et al.'s paper yet, especially not as the findings of their paper are corroborated by many studies. Having said that, I don't have a problem with Moburg's paper and it doesn't really matter which is used for your rebuttal.

Oh, and there's a wee mistake in line 4 - "There are several holes with this line of thinking and they will be discussed here".

2010-08-17 03:18:54Comment
Robert Way

robert_way19@hotmail...
24.224.230.22
I think the reason enough to not consider mann's paper has been proven. His reconstruction using EIV does not validate past 1500 if one does not use tree rings or the tiljander proxy series (which Mann used upside down). Furthermore, his previous work shows that it does not capture centennial scale temperature changes associated with natural variability. That being said I do think he has provided a lot of good work to the scientific community but I still cannot trust that showing mann's curve wouldn't be a lightening rod for criticism.

Finally, with respect to the uncertainty. I agree there are uncertainties which should be indicated in the intermediate version but I feel like the basic version shouldn't be filled with maybe's. We do know that the MWP was not warmer globally compared to today. Even in the warmest areas to have felt its effects (Northern Canada, Greenland, Northern Europe) more and more proxies are showing that the 21st century to now (2000-2010) has shown warming in excess of measured during the MWP. I will look through and see if there are a couple specific points where I can show in a bit of uncertainty but can you point out perhaps a few locations where you feel I should add in?


I also agree that the sensitivity issue, (though a great idea in the intermediate post) is likely beyond what the basic reader would be seeking with respect to this rebuttal.
2010-08-17 17:48:23A slight change
gpwayne
Graham Wayne
graham@gpwayne...
86.156.59.156

Hi Robert,

I keep falling over this line, and I would like to suggest a change:

"One of the most often cited arguments of those sceptical of global warming is that the Medieval Warm Period was as warm as/warmer than today and that this proves that we cannot be causing current warming".

I feel you are putting the denialist argument rather baldly here. Would this be more appropriate perhaps?:

"One of the most frequently cited sceptical arguments is that the Medieval Warm Period was as warm, or even warmer, than today, Since the MWP warming was caused by natural events (and not mankind), the current warming is probably also a natural phenomenon".

2010-08-17 20:50:04
Anne-Marie Blackburn
Anne-Marie Blackburn
bioluminescence@hotmail.co...
80.42.219.219

Hi Robert. The only reason I mentioned uncertainty is that many contrarians like to say that we've stated the science is settled. It seems they are almost resentful about it so I've become quite wary. Obviously it's your post and my objection is only minor.

I don't want to get into an argument about Mann's paper. Perhaps the best way to move on is to mention that many studies have found that the MWP was unlikely to be warmer globally and point to the NAS report which reviewed the relevant literature. What do you think?

The rebuttal is more or less ready to go though - good work :)

2010-08-17 22:27:12REVISED-MWP was warmer!
Robert Way

robert_way19@hotmail...
24.224.230.22

Medieval Warm Period was warmer

What the science says... While the Medieval Warm Period saw unusually warm temperatures in some regions, globally the planet was cooler than current conditions.

One of the most often cited arguments of those skeptical of global warming is that the Medieval Warm Period was as warm as/warmer than today. Using this as proof that we cannot be causing current warming is a completely inappropriate argument which is based upon a faulty argument. Several holes with this line of thinking will be discussed here:

First,
evidence suggests that the Medieval Warm Period was in fact warmer than today in many parts of the globe such as in the North Atlantic thereby allowing Vikings to travel further North than had been previously plausible (Due to sea/land ice reductions). However, evidence also suggests that some places were very much cooler than today including the tropical pacific. All in all, when the warm places are averaged out with the cool places, it becomes clear that the overall warmth was likely similar to early to mid 20th century warming. Since that early century warming, temperatures have risen well-beyond those achieved during the Medieval Warm Period across most of the Globe according to the National Academy of Sciences synthesis of climate reconstructions (http://books.nap.edu/openbook.php?record_id=11676&page=R1).

Secondly,
the Medieval Warm Period has known causes which explain both the scale of the warmth and the pattern. It has now become clear to scientists that the Medieval Warm Period occurred during a time which had higher than average solar radiation and less volcanic activity (both cause warming). New evidence is also suggesting that changes in ocean circulation patterns played a very important role in bringing warmer seawater into the North Atlantic thereby explaining much of the extraordinary warmth in that region. These causes of warming contrast significantly with the current warming which we know cannot be caused by the same mechanisms.

Overall the take home message is that
a) Globally temperatures are warmer than they have been during the last 2000 years, and
b) the causes of Medieval warming are not causing late 20th century warming.


2010-08-17 22:29:54Hyperlinks
Robert Way

robert_way19@hotmail...
24.224.230.22
Anyone know how to show hyperlinks like the NAS one? Thank you for the comments and contributions
2010-08-17 22:44:30
Anne-Marie Blackburn
Anne-Marie Blackburn
bioluminescence@hotmail.co...
80.42.219.219

Ready to go for me, though I would perhaps try to simplify the last sentence of your first point - something along the lines "Since that early century warming, temperatures have risen well-beyond those achieved during the Medieval Warm Period across most of the Globe. This is confirmed by a National Academy of Sciences report on climate reconstructions." Though maybe that's nit-picking.

Not sure what you mean with your question on hyperlinks - could you elaborate?

2010-08-17 23:27:50Comment
Robert Way

robert_way19@hotmail...
24.224.230.22

 Yeah I don't know how you just made that report clickable. I'd like to have it as a link so someone can go right to the report. I will revise the last sentence.

2010-08-17 23:31:23
Anne-Marie Blackburn
Anne-Marie Blackburn
bioluminescence@hotmail.co...
80.42.219.219
Oh right. It's the same principle as when you want to make some piece of text bold in Word - you select the text you want to turn into a link, click on the Insert/Edit link icon (6th icon on the second line), enter the URL into the first box, click insert, et voila!
2010-08-18 14:55:08
Brendon

bpywell@iinet.net...
124.170.75.247

Looks great Robert!

Should there be a footnote as to why we're showing a graph of Northern Hemisphere only as opposed to a Global reconstruction, especially since we're arguing that it wasn't a global effect?

Also, I think the second point is very important. Even if the MWP was warmer than today, the reasons for the warmth are different from that of the current warming. It would be good to have this point incorporated into the Intermediate level rebuttal too.

And maybe it's just me, but when I read higher than average solar radiation and less volcanic activity (both cause warming) I thought, hang on volcanic activity causes cooling, it took me a few moments to realise oh yes, less volcanic activity causes less cooling. I wonder if this wording could be improved?

2010-08-18 21:40:58Comment
Robert Way

robert_way19@hotmail...
24.224.230.22
I'll have a look at that sentence and make it less clunky and try and make it clearer on the graph that its NH temps. One of the points of the graph though is to show that even in the region supposed to have felt the most warming (the northern hemisphere) temperatures are still beyond those seen.
2010-08-19 00:02:05POST-UPDATED
Robert Way

robert_way19@hotmail...
24.224.230.22
Post has been updated, see top of page for update
2010-08-19 05:43:40Thumbs up w/two little caveats
doug_bostrom

dbostrom@clearwire...
184.77.83.151

"...completely inappropriate argument which is based upon a faulty argument." Awkward. Maybe "premise" for second "argument?"

Also the floating "First" and "Second"  above the two main rebuttal chunks bug me a little bit but maybe that's just my own idiosyncrasy? 

 

2010-08-19 06:29:40Comment
Robert Way

robert_way19@hotmail...
142.162.181.139
Doug I tried to fix up that sentence but it is clunky. Let me know if you have any more suggestions.
2010-08-19 06:44:09Better than my suggestion
doug_bostrom

dbostrom@clearwire...
184.77.83.151
Rhetoric versus science. Perfect choice of words and it does not "clunk" for me.
2010-08-19 07:43:50Comment
Robert Way

robert_way19@hotmail...
142.162.181.139
Thanks. Now hopefully get it up and posted soon!
2010-08-20 21:43:25Comment
Robert Way

robert_way19@hotmail...
24.224.230.22
Any thumbs?
2010-08-21 02:17:13Is this a basic rebuttal and does it have a number?
John Russell

jr@johnrussell...
84.92.176.215

I can always tell the scientists because they tend to end their opening paragraphs with a superflous comment, like...

"Several holes with this line of thinking will be discussed here." :-)

How about, "So what are the holes in this line of thinking?"

Other suggestions...

1) "...to travel further North than had been previously plausible". Is this actually the right word? How about 'possible'. And to avoid it being a split-infinitive it should be "...possible previously".  

2) Can I suggest you use a few more commas, Robert -- it'll help to make it more readable in places. For instance,  "New evidence is also suggesting that changes in ocean circulation patterns played a very important role in bringing warmer seawater into the North Atlantic (comma) thereby explaining much of the extraordinary warmth in that region"(big intake of breath). Even better add a fullstop (period) and start again with, "This explains..."

3) "b) the causes of Medieval warming are not causing late 20th century warming". To avoid ambiguity can I suggest; "b) the causes of Medieval warming are not the same as those causing late 20th century warming".

Best wishes,

JR

2010-08-21 04:51:33Revised
Robert Way

robert_way19@hotmail...
24.224.230.22
Suggestions accepted and revisions completed. Thanks JR
2010-08-21 04:56:32
doug_bostrom

dbostrom@clearwire...
184.77.83.151

Almost there, Robert!

Having said that and even though I've already cast my vote, I wonder if some slightly more explicit but brief words as to why the MWP is even relevant here are in order?  The MWP thing reminds me of the general "climate has changed in the past" issue.

On the other hand, you can perfectly well ignore this... :-)

2010-08-21 06:51:40Thumbs up
John Russell

jr@johnrussell...
84.92.176.215

Robert; it gets my thumbs up.

One last suggestion I've spotted. Near the end you refer to 'current warming'. As you've referred to ocean currents more than once, can I suggest you change this use of the word 'current'?  For instance, try...

" These causes of warming contrast significantly with today's warming, which we know cannot be caused by the same mechanisms."

Best wishes,

JR
   

2010-08-21 16:57:36You get the thumb...
gpwayne
Graham Wayne
graham@gpwayne...
217.44.86.17

One small thing: "...the Medieval Warm Period was as warm as/warmer than today". I'm sure this would be easier on the eye if it just said "...the Medieval Warm Period was as warm, or warmer, than today".

That doesn't stop me giving it the thumb though...nice one.

2010-08-21 17:20:26Twitter title suggestion
gpwayne
Graham Wayne
graham@gpwayne...
217.44.86.17

Medieval Warm Period: 'global' claim factual  - like Camelot!

2010-08-22 08:41:19
Andy S

skucea@telus...
66.183.162.8

Some nit-picky suggested changes to the second paragraph, highlighted in yellow.

 Firstly, evidence suggests that the Medieval Warm Period was in fact warmer than today in many parts of the globe such as in the North Atlantic. This warming thereby allowed Vikings to travel further Nnorth than had been previously possible because of reductions in sea ice and land ice in the aArctic. 

"Firstly" is consistent with your later use of "Secondly".  And see here for guidance on capitalizing compass points etc (I screw this up all the time, btw).

Also, I would like more embedded/hyperlink references; for example to Moburg et al (2005) and to support the claim that "New evidence is also suggesting that changes in ocean circulation patterns..." I realize that this is a basic text but I think that we should all uses these texts as a means to point the new reader to more reading and to demonstrate that we are not just making this stuff up.

 Otherwise, I think this is ready to go!

2010-08-22 20:10:12I don't like one sentence
nealjking

nealjking@gmail...
91.33.112.96

"Overall the take home message is that": This sentence seems to place the whole text into the context of a public-relations tactic, rather than as a straightforward discussion.

I would prefer something like: "Our conclusions are:"

Regards,

Neal J. King

 

2010-08-23 01:51:37Revised
Robert Way

robert_way19@hotmail...
142.162.177.145
Revision is done.
2010-08-23 02:56:53Picking a nit
nealjking

nealjking@gmail...
91.33.112.96
"including the tropical pacific" => "including the tropical Pacific"
2010-08-23 09:34:48Published
John Cook

john@skepticalscience...
124.178.185.124
Robert, I've just published this one. Well done, I thought this was a fantastically structured rebuttal.
2010-08-25 21:59:59Layout suggestion and typos
James Wight

jameswight@southernphone.com...
58.105.164.221
Reading over the published version of this it occurred to me that the paragraph beginning “Firstly…” is too long. It’s all important information, but we don’t want the reader to fall asleep, so I suggest splitting this into two paragraphs.

I also found a typo – there should be a full stop after “…bringing warmer seawater into the North Atlantic”

I also glanced at John Cook’s intermediate version of this rebuttal and noticed a couple of typos there as well, so I’ll try and get his attention. (Namely, one sentence reads: “In some areas, temperatures were even even warmer than today.” And another ends in a full stop instead of a question mark: “How does the Medieval Warm Period compare to current conditions.”)