I have been having a long discussion with Mr Mouse on this thread at leftfootforward. Mr Mouse states that there is a basis for everything he writes, and claimed that it was far hotter in the Northern Hemisphere during the Medieval Warm Period (MWP) than it is today. I pushed him on this claim because I wanted to see the evidence for it.
At present he hasn’t found the evidence to substantiate his claim, but like him I often know I have read something somewhere but for the life of me can’t find where it came from, so I am not in anyway claiming that Mr Mouse was trying to deceive.
I tracked down some Greenland ice core data. You can download it here and I think that this might be the data that Mr Mouse refers to, the location of where the ice core was taken from can be viewed here. Since Anthony Watts from Watts Up With That so nicely plots the data for me I’ll not plot them again.
Figure 1 shows the MWP centring on the year 1000 ad very strongly. The left hand column is temperature in Celsius (I had to check the original data I linked to above to confirm the temperature scale) and it shows that temperature during the MWP was close to 1.5 degrees warmer than the year 1800 and it also shows temperatures climbing from around 1850 onwards.
Figure 1
Now Figure 1 finishes around 1905 so if we wish to compare temperatures during the MWP and today we need to know what has happened since then. I do not know the reasons why the ice core data finishes in 1905 (The year the ice core was taken was 2000). Anthony Watts suggests that at least another 0.5 degrees needs to be added to the end of the graph to account for recent warming, which means that temperatures today would be 0.7 degrees cooler in the Arctic than during the MWP. I don’t know where he got his figure from, it might be one of the lower estimates for global warming since 1905. What Mr Watts ignores is that temperature rises in the Arctic and this includes Greenland have been significantly larger than the rises in the global average. The plot below which comes from the Arctic Monitoring Assessment Program shows the temperature rise in the Arctic since 1900.
Figure 2
It looks to me that the temperature has risen another 1.7 degrees not 0.5 since 1905 and that would indicate that temperatures are 0.5 degrees warmer in the Arctic today than they were during the MWP.
What we have so far missed out is the difference between a regional temperature change and global temperature change. Large parts of the Northern Hemisphere show evidence that the MWP was a widespread climate phenomenon but not universally throughout the Northern Hemisphere. Ice cores from Antarctica do not show any evidence for the MWP, secondly evidence from Australia suggest that temperatures were not unusually warm during the MWP and could even have been cooler. The evidence from the Southern Hemisphere is very patchy and any scientist would be hard pressed to make a case that in the Southern Hemisphere during the MWP temperature changes matched those in the Northern Hemisphere or that they were cooler.
Philip Machanick has more information on the MWP in this blog piece.
When looking at the ice loss plots in Philip’s blog piece I think that one of the biggest problems with the IPCC is that it has been far too conservative when looking at ice loss in Antarctica and Greenland, and also the loss of Arctic sea ice when you actually compare what has been happening to what was predicted.
Summing up. The evidence here suggests Greenland temperatures during the MWP were approximately 0.5 cooler than today. There is no convincing evidence that the MWP was a global phenomena indicating that global temperatures are likely to be higher today than they were during the MWP. More data would be needed to make a more conclusive statement.
#1 by Arthur Reader on April 21, 2010 - 1:10 am
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That analysis is truly pathetic. The only way to accurately compare the MWP with the modern warming period is to use the same proxy for both or with proper calibration make the case for both.
In this case, the “temperature record” for the Arctic is a statistical composite of many records, which include some extremely dubious Siberian records which show spurious warming due to a) the growth of the cities and b) the ending of the fuel subsidies with the collapse of the Soviet Union. See http://www.warwickhughes.com/climate/tamyr.htm for an example.
The statistical composite combines many records which have different variances, artificially decreasing the variance in the final result.
The nearest station is the long Godthab-Nuuk temperature record http://data.giss.nasa.gov/cgi-bin/gistemp/gistemp_station.py?id=431042500000&data_set=1&num_neighbors=1 . It shows clearly that the warmest period was the 1930s and 1940s, not the 1990s or 2000s.
The single proxy of the Greenland IceCore shows that the MWP was warmer than the modern warming period. Get over it.
In the least few days yet another study shows the MWP and LIA in Indonesia http://wattsupwiththat.com/2010/04/20/another-indication-of-mwp-and-lia-being-global
There are many, many more studies which the CRU cabal didn’t manage to suppress which show that the MWP really was a global phenomenon, something that Michael Mann explicitly denied.
I can hardly believe such crap logic from Oxford University, but then standards have fallen in the rush for grant money.
#2 by Oxford Kevin on April 21, 2010 - 8:37 am
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Thank you Arthur for your comment.
Just so you know, I am not associated with Oxford University in any way. Interesting assumption. Your description of the people from CRU as a cabal is also instructive.
My post proves nothing. The point of the post was in response to Anthony Watts’ piece which is continually referred to by sceptics as proof that the MWP was warmer than today and that this was assumed to be globally. In the same way Anthony Watts’ post proves nothing. All I can say is that the evidence is not conclusive, and I am skeptical that a single climate proxy shows that the MWP was warmer than current temperatures as you suggest.
The Weather station you refer to is on the coast, and moderated by the ocean?
Whilst the Greenland ice core is from near the centre of Greenland.
As to the study you refer to, you do realize that the proxy data is all from locations very near the equator, and this is meant to make me believe that this is indicative of the temperature change in the Southern Hemisphere. It is further evidence and good to have but by itself does not change the impression that the MWP was not global.
#3 by Dr Michael Cejnar on April 25, 2010 - 1:06 pm
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Dear Oxford Kevin
While single posts indeed prove little about MWP, CO2 Science has done an impressive collation of evidence for MWP being warmer than today, arising from 752 scientists from 442 institutions in 42 countries.
Study:
http://www.co2science.org/data/mwp/mwpp.php
Interactive Java map:
http://www.co2science.org/data/timemap/mwpmap.html
Can yo refute the weight of that evidence?
Regards
#4 by Oxford Kevin on April 25, 2010 - 9:10 pm
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Michael, thanks for your comment.
In response to a different question, I was pointed to a recent piece on co2science . I have often been skeptical of blog posts and their interpretation scientific papers, so for the first time I decided to followup on my skepticism and contacted the author of the original paper, the response of the lead author confirmed my skepticism.
I cannot refute all the work done on the MWP by CO2 science but my one and only experience suggests to me that I should not rely on CO2 science as a reliable source.