Bishop Hill IPCC to admit MWP warmer?
Aug 21, 2013 Climate: MWP The Washington Post has further leaks from the IPCC's Fifth Assessment Report. They can be seen here.
The conclusions about the millennial temperature reconstructions...
The 30 years from 1983-2012 was very likely the warmest 30-year period of the last 800 years.
are interesting when compared to what was said last time round:
Average Northern Hemisphere temperatures during the second half of the 20th century were very likely higher than during any other 50-year period in the last 500 years and likely the highest in at least the past 1,300 years.
The shift from 50-year periods to 30 years periods makes direct comparison difficult, but this does seem to suggest something of a reining back. The Medieval Warm Period, located by AR4 in the centuries spanning the end of the first millennium, is now apparently accepted as probably being warmer than the current warming, at least if the Washington Post is to be believed.
Reader Comments (59)
omnologos (Aug 21, 2013 at 11:44 AM) says:
"...The idea that the new 95% figure is suddenly scientifically sound, is beyond risible...."
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omnologos
The 95% assertion is wholly illogical unless the temperature stasis post the late 1990s can be explained and the said explanation is consistent with AGW.
As I understand matters it is accepted that presently there is no clear explanation for the lack of continued warming (slow down in the rate of warming) these past 16 or so years (depending upon which data set is used). Prima facie, the lack of warming/slow down in the rate of warming is not only not consistent with AGW, it runs contrary to it.
That being the case, and given that at the time of 4AR there was only 90% confidence that the late 20th century warming was anthropogenic, there cannot today be more confidence in the cause of the warming these past 50 or so years (ie., post 1940, or 1950) unless and until the recent pause in the warming can properly be explained in a manner that is consistent with AGW with a confidence level not less than 95%. Put simply: if at a time when one considered that one can fully explain all changes in the temperature record with 90% confidence, it is impossible to now, when there is a period in the temperature record that cannot be explained, to assert that there is now a greater degree of confidence than there was at a time when everything could be explained.
Until such time as an explanation consistent with the AGW ‘theory’ for the recent pause/slow down in the rate of warming is forthcoming, the claim of 95% confidence in AGW is patently absurd. As you say, it is "beyond risible."
NO ONE seems to have responded to the Wash Post's Jason comment yet. His extracts invite some critical thinking about paleoclimatology.
Now, consider these three assertions serially: "the period 1983–2012 was very likely the warmest 30-year period of the last 800 years (high confidence)...."
This assertion will not surprise anyone here; but do we REALLY have 'highly confident' decadal temperature measures going back 800 years for the globe?
Next, "...and likely the warmest 30-year period of the last 1400 years (medium confidence)."
do we REALLY have 'medium confidence' in decadal temperature measures going back back another 500 years?
Finally, to this last claim: ""Continental-scale surface temperature reconstructions show, with high confidence, multi-decadal intervals during the Medieval Climate Anomaly (950−1250) that were in some regions as warm as in the late 20th century. These intervals did not occur as coherently across seasons and regions as the warming in the late 20th century (high confidence)."
To restate it, "These [multi-decadal warm] intervals [during the MWP] did not occur as coherently across seasons and regions as the warming in the late 20th century (high confidence)."
So - the global data gleaned from paleoclimate proxies from about one-thousand years ago on a 'continental-scale' is more complete or 'coherent' - seasonally and regionally - than the surface temperature records of the late 20th century? And it is comparable in quality?
Excuse me, but isn't this another one of the 'watch the pea under the pod' issues that Steve McIntyre perennially warns his readers about? Don't updated proxies for the late 20th century show more, much cooling inconsistent with directly measured thermometer temperatures? If so, how can any 'high confidence,' much less 'medium confidence,' be placed in any such 'conclusions?'
Like many others here at BH, the more I read any 'establishment' generalizations about paleoclimatology the more I think climastrology and wishful 'thinking.'
Orson: Thanks for replying to Jason in detail. It would have been a pity if my flip comment at the time was the only response. It was very good of the Wash Po guy to drop by.
Orson
I agree with your analysis, including the reference to the pea under the thimble. BEST temperatures have at least one-third of recording stations showing a declining trend which would seem to add weight to the argument that global warming is a myth and always was. Climatic trends are regional not universal and no, there is no justification to my mind for high confidence in using "reconstructed" continental temperatures from 1000 years ago to draw conclusions about the (purely putative) global temperature of the last 30 years.Aug 22, 2013 at 5:46 AM | Orson
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One can never have high confidence in any proxy reconstruction. In fact, I would doubt that one could even have medium confidence in any proxy reconstruction. Personally, I take all proxy records/reconstructions with a pinch of salt other than the ice records which I do consider have some worth.
I attach more weight to historical/archaelogical evidence but that its not usually quantative, but some conclusions can be reached from accounts contained in written records and archaeologicla digs/findings. For example, enough for us to know that Greenland must have been many degress warmer than it is today during the time of the Viking settlements otherwise they would have been unable to have farmed the land and raise live stock.
The only temperature record that we can have medium to high confidence in is the thermometer record (well at any rate before 'the Team' got their hands on it, and it became bastardised by endless adjustments/homogenisations, and before it became contaminated by UHI, station siting issues and station drop outs etc). I say medium to high confidence because there are inevitable issues regarding equipment maintenance (a recent article suggested that degradiation in the stevenson screen could lead to a warming bias of up to as much as 1.5degC), calibration, accuracy of old equipment, sighting/paralax errors, time of recording errors/uncertainties etc.
CET is the oldest thermometer record. But even that is less than 400 years old, We can have medium to high confidence in CET (provided that suitable error bars are included to take account of the points raised in the paragraph above and to take account that in the early days we have no idea what thermometer screen was used). There are some other European records nearly as old which can be used to supplement CET to a wider area and it also appears that CET trends in itself is not a wholly bad proxy for the medium high latitudes of the Northerm Hemisphere (say ~30 to 55degn). But other areas of the globe are without cover until well into the 19th century.
It is patently unscientific to suggest that there is anything more than low to medium confidence in global temperatures for a period extending back before about the mid 19th century, and Northern Hemisphere temperatures extending back before the the late 16th century/early 17th century.
One major issue in Climate Science is the lack of recognition in the limitation of the available data. Most of the data is not fit for the purpose to which it is being put and is being overstarined. Climate Scientists need to be more honest with the appropriate error bars.
I have this ongoing problem with threads like this one.
My fingers persistently want to take the 'r' out of 'proxy'.
I also keep asking the question: Since the majority of standard printers' output is A4, would this be wide enough to include the error bars?
"Greenland must have been many degress warmer than it is today during the time of the Viking settlements otherwise they would have been unable to have farmed the land and raise live stock."
richard verney
If you wish to infer that Greenland was warmer than today when the Vikings farmed between 900AD and 1400AD, you need to define the minimum temperature required for such farming. For example, they grew barley for beer. What is the minimum temperature at which a barley crop can be grown? Data, please.
Note that I am quite content with the possibility that the MWP was warmer than today. That's within the error bars of Marcott et al. What I'm seeking from you is temperature numbers inferred from your qualitative statements.
Entropic Man
Further to your post at Aug 23, 2013 at 1:27 AM.
See geneerally my post at Aug 22, 2013 at 2:33
All proxies should be regarded with a pinch of salt as far as any attempt is made to infer past temperatures. Proxies are not thermomemeters, and respond to favourable environmental conditions in general and not to temperature in insolation such that any reconstruction of past temperature from proxies is an inference, not a fact.
It is all but impossible to callibrate and tune proxies to the temperature scale that we deal with. Mann found this with his tree rings. If I recall correctly, he tuned them to the period ~1910 to ~1960. By the time they reached ~1960 temperatures being derived from the proxy were diverging from those of the thermometer record. The tree ring proxy was suggesting that post 1960 temperatures were falling, not rising as the thermometer record showed. This is a classic illustration of the problem. The tuning for the period ~1910 to~1960 gave a by chance similarity. But that similarity in response was co-incidendal and hence the divergence post 1960. Had Mann tuned the proxy to the period post 1960 to the late 1980s when the ring proxy data was showing falling temperatures, he would have obtained a completely different past reconstruction.
You will note from my earlier post that once outside CET, we cannot begin to assess Northern Hemisphere temperatures with any degree of certainty. That said, we can make some inferences, which are necessarily qualative in nature since they are not extracted from a thermometer reading, as to the general order of things. As far as greenland, we know as fact from archaelogical evidence:
1. As the glacier retreats we are finding remains of Viking Settlements. Since the Vikings did not (indeed could not have) constructed and erected their settlement under a glacier, the glacier in Viking times was not as extensive as it is today. This establishes that Greenland (in this area) was at least as warm as today.
2. the Vikings in these settlements farmed the land. However, the land being revealed around somne of these settlements is perma frost. It canot be farmed today even with our advanced farming technologies. The Vikings only had primitative technology in comparison and nu greenhouses or polytunnels or efficient fertilisers etc. This establishes that Greenland (in this area) was warmer than today. The Vikings could not have farmed land that was perma frost.
3. This past winter in the UK it was harsh. You probably saw the many news reports on farmers losing sheep and cattle particularly in hillside farming areas in Wales and Scotland. Just to remind you, see for example http://www.fwi.co.uk/articles/02/05/2013/138888/big-freeze-livestock-death-toll-hits-100000.htm You will note that the death toll compared to 2012 (which was also a harsh winter) was up 64,000. The death toll in 2012 was also higher than the 30 year average for the 'climate norm' temperatures. So two harsh winters in a row had a severe impact on farming, and I recall reports stating that a number of small farmers were giving up farming (notwithstanding that they no doubt had some insurance to cover losses or government compensation scheme whereas such schemes were not available to the Vikings).
5. When considering farming, one must remmber that the Vikings did not have tractors so response over ground would have been slow particularly where snow drifts were deep. Cattle and sheep require significant volumes of water. This is a problem today for farmers when water freezes Just stop and consider how the Vikings would cope with supplying sufficient quantities of fresh water to their livestock when conditions were harsh. They did not have huge water storage tanks, let alone heated tanks, and no hoses and pumps to run out supplies.
6. The Vikings could not have survived on Greenland for several centuries if life had been at subsistence level. One harsh winter, or certainly two consecutively, would have ended the settlement. The farming conditions in relative terms must have been boutiful, for them to have survived such a lengthy time on the island.
Whilst it is difficult to put a precise figure on temperature, we know that Greenland must have been as warm and benign as the Scottish Highlands, and possibly even the Welsh borders, for people with primitive farming technology to eek out a survival for hundreds of years. That means that Greenland must have been several degrees warmer than today.
Now I do not know how extensive those conditions were throughout the Northern Hemisphere in general. However, if CO2 is a well mixed gas and if CO2 controls temperatures, there is no obvious mechanism that would produce warm conditions in Greenland and only there.
There is no reason to presume that Greenland was a unique, special and isolated case enjoying its own special micro-climate (especially since there are records of olive trees being grown in Germany and more extensive vinification) . But if it was, what caused this? Anyone claiming that Greenland was so unique and an isolated case needs to explain the special conditions that greenland encountered and why and how these arose and dissipated.
Do you have an explanation? If so I would be interested in your theories.
richard verney
Concur!
The fact that evidence is (and in this case must be) anecdotal does not necessarily make it any the less evidence.
While not of the same quality as accurately recorded temperatures the situation you describe would appear to be as reliable as most other proxies when it comes to determining temperatures relative to today.
Unless of course you are obsessed with the idea that variations of less than 0.5 degrees is somehow evidence of impending doom.
Pepys' diaries are also helpful as are the figures for the price of wheat over the centuries ago and the observations of sailors and others who, not having the incentive of continual grant funding to consider, we have to assume were recording what they saw because it was of interest or relevant to their day-to-day living.