From the Institute for Hydrography, Geoecology and Climate Sciences comes this paper that is just one more piece of evidence that the Medieval Warm Period was global, and not regional.
Mapping Medieval Climate Change in Africa:
Continental warming, coastal cooling and shifting rainbelts 1000 years ago
Global climate is currently undergoing major change. Experts agree that this change is driven by a combination of man-made and natural factors. However, full quantification of the anthropogenic and natural components is still a matter of debate. In order to better understand the contribution of natural climate variability and distinguish this from man-made influence, researchers worldwide have gone out to the field to study Earth’s pre-industrial climate history. Of particular interest are the past thousand years, which in Europe and North America have seen the transition from a rather warm medieval period to major cooling of the Little Ice Age, followed by the temperature rebound of the Current Warm Period which was further intensified by human greenhouse gas emissions. Our understanding of medieval climate outside this well-studied North Atlantic region is unfortunately still poor.
An international team led by geoscientist Sebastian Lüning wants to change this. Lüning is a professional resources geologist who in his sparetime works on paleoclimatological studies with the Switzerland-based Institute for Hydrography, Geoecology and Climate Sciences. Together with colleagues from Poland, Nigeria, Turkey and Germany they embarked on a journey through the scientific literature to shed light on the so-called ‘Medieval Climate Anomaly’, a period comprising of the years 1000-1200 AD. The initial focus region of their study was Africa. Lüning and his team crawled through hundreds of publications and mosaiced together a fascinating picture of African medieval climate change that tracks ancient heat waves, local cooling, drought and phases of amplified rainfall. Using modern database and visualization technology, the team managed to synthesize astonishing trends from the large amount of filtered data. Lüning explains the challenge:
“This was true detective work. Obviously, we do not have any thermometer measurements or satellite data from medieval times. Scientists therefore analyze natural archives, namely sediment cores from the ocean floor, lakes and peatlands, as well as cave dripstones. Layer by layer the climate history is recorded like in a geological book, recorded by changes in geochemistry and fossil content. These property variations are then geologically translated back into climate parameters. Radiocarbon age dating provides the necessary time orientation”.
All published data were initially collected on a Google Map. The recorded climate development was then thoroughly correlated across the region and resulting temperature trends were mapped out. The vast majority of land sites in Africa showed a characteristic warming during the Medieval Climate Anomaly, in line with similar warming in Europe and North America. The situation in the coastal seas surrounding Africa, however, was different. Changes in the wind systems intensified the upward transport of deeper cooler water to the coasts, which resulted in a marked medieval cooling in the so-called ‘upwelling’ zones. Nevertheless, the areal extent of these narrow coastal sectors is rather small when compared to the total area of the African continent. The study was published in the journal Paleoceanography and is based on 44 study sites in and around Africa.
Besides temperature, Lüning and his group were also interested in medieval shifts in rainfall. An improved understanding of natural variability of rainfall is crucial, especially for the semi-arid and arid parts of Africa that heavily depend on seasonal rainfall for drinking water, agriculture and food production. Lüning describes the significance of this work:
“Our initial simplistic expectation was that we would find a uniform continent-wide medieval change in rainfall. However, this was not the case. As rainfall belts shift, some areas get drier and others wetter. It is important to understand these natural changes of rainfall patterns and their ultimate drivers. These are key calibration input data for climate models that still struggle to simulate regional rainfall correctly.”
The study identified three areas in Africa in which rainfall increased during the Medieval Climate Anomaly, namely Tunisia, western Sahel and the majority of southern Africa. At the same time, a reduction in precipitation occurred in the rest of Africa, comprising of Northwest and Northeast Africa, West Africa, Eastern Africa and the Winter Rainfall Zone of South Africa. The latter region includes Cape Town that currently suffers from a multi-year drought that has led to a serious shortage of drinking water. Similar droughts appear to have existed here during medieval times when the rain-bearing westerly winds were pushed so far south and away from land that they no longer intercepted the continent. The hydroclimate study has been published on 12th February in the journal Palaeo3 and is based on 99 sites in Africa.
In the absence of pre-industrial atmospheric CO2 variations, natural drivers have to be invoked to explain the observed medieval climate change. The most promising candidates are changes in solar activity as well as ocean cycles, which operate on times scales ranging from decades to millennia. The two new studies from Africa emphasize the great significance of natural climate variability on a global scale. A robust understanding of the natural ‘climatic heartbeat’ is essential. Ultimately, it will allow to better distinguishing between anthropogenic and natural contributions to modern climate change and will improve the predictive skill of climate models.
The two African climate reviews are based on a great number of published palaeoclimatic case studies which involved hundreds of scientists. Despite major progress in the field over the past 15 years, large parts of Africa are still white space when it comes to climate reconstructions of the past 1000 years. A dedicated structured research program is necessary to fill these important gaps. Climate policy depends on a robust foundation of such data. Compared to its large share of nearly one quarter of the world’s landmass, data from Africa and Arabia are significantly underrepresented in global temperature reconstructions of the past 2,000 years, an imbalance which needs to be swiftly and effectively addressed.
Papers:
Lüning, S., M. Gałka, F. Vahrenholt (2017): Warming and cooling: The Medieval Climate Anomaly in Africa and Arabia. Paleoceanography 32 (11): 1219-1235, doi: 10.1002/2017PA003237.
Lüning, S., M. Gałka, I. B. Danladi, T. A. Adagunodo, F. Vahrenholt (2018): Hydroclimate in Africa during the Medieval Climate Anomaly. Palaeogeogr., Palaeoclimatol., Palaeoecol., doi: 10.1016/j.palaeo.2018.01.025. The paper can be freely accessed until 11 April 2018 using this link: https://authors.elsevier.com/a/1Wbbe73Nzqmc1. Please also download the Data Supplement (link on left side of article page) which contains the detailed site proxy correlations.
About the Institute for Hydrography, Geoecology and Climate Sciences (IFHGK), and the medieval climate project:
The Institute was founded in 2017 by Dr. Hans-J. Dammschneider, who also serves as Chairman. The Institute conducts and supports research in the field of geosciences, with a focus on natural climatic drivers and their role in pre-industrial and modern climate change. The two African review papers form part of the Medieval Climate Anomaly Mapping Project which in its startup phase has been kindly supported by crowdfunding. No other funding has been received.
Nick or Steven: Need some help from you. I’ve downloaded the GHCN Monthly files, but I can’t find a station metadata file. The README gives the format of the metadata, but darned if I can find a file with it. The station metadata file for the daily (*.dly) files uses a different ID format, though in some cases the WMO_ID number matches positions 4-8 of the GHCN Monthly ID. However, I can only match up 4483 out of the 7280 in the Monthly file.
Do you know where NOAA hides the station metadata file for the Monthly data?
Thanks!
James,
It sits within the same tar.gz file as the data, eq ghcnm.tavg.latest.qcu.tar.gz, here. It has the same stem as the data file, but a .inv suffix instead of .dat. Although they give a different file for each .dat (by date or adjusted status) they are always the same.
Thanks. However, there’s only 5795 station IDs in the .inv file. Is that the number of working stations now, and not 7280?
James,
There should be 7280. I post a station list here which is derived from the .inv file. Just press the “GHCN Stations” radio button at the top of the frame. Alternatively, I have posted a .inv file here
I loaded the file ghcnm.tmax.v3.3.0.20180224.qcu.dat into my Oracle database, ran the query “select count(distinct id) from ghcn_monthly_24_feb_2018;” and got 5795, which matches the number of IDs in the .inv file that came in the file you linked to above.
After further review, the ruling on the field is confirmed: there are only 4483 station ids in both the .dat and .inv files for a NOAA monthly data release.
SQL> select count(distinct id) from ghcn_monthly_24_feb_2018;
COUNT(DISTINCTID)
-----------------
5795
SQL> select count(id) from ghcn_monthly_station_metadata t1 where not exists (select 1 from ghcn_monthly_24_feb_2018 t2 where t2.id = t1.id) order by t1.id;
COUNT(ID)
----------
1485
SQL> select 5795+1485 from dual;
5795+1485
----------
7280
Accidentally used the 4483 number from my attempt to match the WMO IDs to the substring from the Monthly IDs. That should be the 5795 number from the actual count of the IDs in the .dat and .inv files., and from my database count.
James,
The file I linked has 7280 lines, one station per line. You are counting distinct station ID’s. But are you including all 11 digits? There are many cases where stations have the same WMO but a different suffix.
Nick,
Mystery solved. I am looking at the TMAX file, not the TAVG file. The TAVG file has all 7280 stations, while the TMAX file only has 5795 stations. I’m more interested in the TMAX data since I believe it tells more about true warming than the TAVG data does.
Thanks again!
Your supposition that TMAX will tell the whole story is wrong.
The reason is simple:
Here is what I suggest you do:
Avoid Monthly data; Start with GHCN daily. raw. make your own monthly series.
As you can see understanding where all the data is requires some diligence and study. Years in fact.
Next, understand the science. Do we expect Global warming to influence Tmin or Tmax, both? why?
Next, research what has already been published
http://berkeleyearth.org/data/
You can see Tmin, Tmax, and Tavg.
Next, study the various methods for creating a spatial map of temperatures. Decide:
1. Use a published method
2. Design your own
If you choose 2, then you have to test your method. This is typically done with Synthetic data.
http://static.berkeleyearth.org/memos/robert-rohde-memo.pdf
This is how they get their lies to stick in the minds of the masses. Put speculation with facts and the association makes it look like a fact.
“Of particular interest are the past thousand years, which in Europe and North America have seen the:
#1 (data=fact): transition from a rather warm medieval period to
#2 (data=fact): major cooling of the Little Ice Age, followed by the
#3 (data=fact): temperature rebound of the Current Warm Period which was further intensified by
#4 (no data=Unproven speculation): human greenhouse gas emissions.
Well played Sebastian – what a star. Holding down the day job and getting these analyses out too.
weltklima,
we can’t forbid studies that “reckon” the wrong thing. That would make us no better than the alarmist enforcers.
And studies aren’t supposed to be retracted for the crime of being “erroneous.” Errare humanum est. Retraction is reserved for fraudulent papers and those that shouldn’t have survived peer review.
So unless your comment was a clever parody of a censorious Consensus Scientist, I object to it.
I found it interesting that the high point of development of the Angkor complex in Cambodia coincided with cathedral building in Europe. I conclude that agricultural surpluses during the warm periods in both regions provided the economic basis for these vast infrastructure developments.