Posted on 24 April 2011 by Hoskibui
With regularity, you might hear skeptics mentioning a website called CO2 Science and its Medieval Project. It is a front for a research center called Center for the Study of Carbon Dioxide and Global Change and their goal is to distribute:
…factual reports and sound commentary on new developments in the world-wide scientific quest to determine the climatic and biological consequences of the ongoing rise in the air's CO2 content.
The website is run by the Idso family (Craig, Sherwood, Keith and Julene).
One of the Idsos' main projects is to collect references that shows temperature reconstructions of the Medieval Warm Period (MWP). The website lists a large number of sources and diagrams that purportedly show local warming during the MWP, along with the Idsos' interpretations of those. Its main conclusion is that current warming is not unprecedented since there was a lot of warming during that time at various sites.
One of the commonly used methods of "skeptics" is to flood the discussions with large sets of references that supposedly support their point of view, regardless of what the studies in that reference list actually say. It is usually the quantity, not the quality, that counts. This is probably done with the confidence that few of the readers will bother, or have the time or ability, to scroll through the entire list of references to point to problems with the website's interpretation of the studies.
The CO2 Science also has a powerful interactive map where you can find the locations of the studies in their database. By clicking on the dots on the map you get to a page where a summary of that study is displayed - or rather the CO2 Science interpretation of the study.
CO2 Science has also been a useful resource for other skeptics, see for example the Science Skeptical Blog which has also available an interactive map (pictured below):
This interactive map is useful in its purpose: to view the alleged global warming during the MWP in graphical form. It has the feature that if you click on the images, then it shows a temperature reconstruction (or other proxy, see below). There you can also find sources for each graph, with abstracts (actually, the abstracts sometimes tell a different story line than the documents - see below).
Interaction for healthy skeptics?
For people with healthy skepticism these interactive maps are quite good. When I say healthy skepticism I am referring to those who have skeptism for both sides of the argument, not just skeptism about studies that can be interpreted as pro-AGW theory.
So it is crucial that those maps are viewed with a critical mind. On Skeptical Science (as opposed to Science Skeptical Blog) we have looked before at common graphical tricks and the Medieval Warm Period that include the following tricks:
- Hide the temperature scale and/or the temperature values
- Pick one area or location of the world
- Cut out or ignore recent warming
The total effect of those maps, like the one on Science Skeptical Blog - is what is most effective for the casual reader. All of the selected articles on the map show at some point a period that can be interpreted as "Medieval Warming". The quotation mark is because in some cases the research is only about the MWP itself - but not the temperature. For example we can find graphs showing changes in precipitation, like, Zhang et al 2003 - study from Tibet, by which it states in the abstract (emphasis mine):
High-resolution climate proxy records covering the last two millennium on the Qinghai-Tibetan Plateau are scarce yet essential to evaluation of the pattern, synchroneity and spatial extent of past climatic changes including those in the Medieval Warm Period (MWP) and the Little Ice Age (LIA). Here we present a 2326-year tree-ring chronology of Sabina Przewalskii Kom for Dulan area of northeastern Qinghai-Tibetan Plateau. We find that the annual growth rings mainly reflect variations in regional spring precipitation. The greatest change in spring precipitation during the last two millennia seems to occur in the second half of the 4th century. The North Atlantic MWP was accompanied by notable wet springs in the study region during AD 929–1031, with the peak occurring around AD 974. Three intervals of dry springs occurred in the period of the LIA. Our tree-ring data will facilitate intercontinental comparisons of large-scale synoptic climate variability for the last two millennia.
This research is not only notable for the fact that it contains a proxy for precipitation and not for temperature, but also because here the skeptics freely use a tree ring proxy - which they consider mostly unusable (well, unless it can be used to make a point contradicting AGW theory).
Few of the graphs shown in figure 2 show the temperature like it is today; in addition, one trick frequently used is to have the MWP ill-defined. Usually the MWP is the period between 950-1250, but when you look at the graphs you see some inconsistency. It seems that it doesn´t matter for the maker of those websites if it is warm during 800 AD, 1100 AD or even 1400 AD; that warming is - by their opinion - indication of a global warming during the MWP.
If you take graphs from two separate locations you can see some difference. One graph shows a proxy for temperature in Greenland and the other one for New Zealand:
Looking at those two graphs it is clear that the warming is not at the same time.
Another flaw is evident when looking at those graphs: the insistence on using old data. Much of the data is old and outdated. It is difficult to imagine that there are no better and newer data on paleoclimate in New Zealand then a study of oxygen isotopes from the year 1979.
There is also a tendancy to ignore corrected version of data. In the case of this map, they use for example Loehle 2007 instead of Loehle 2008 (See Kung-fu Climate).
The above description above can be used for CO2 Science - and for what can be seen on Science Skeptical Blog. The map on the Science Skeptical Blog actually is better because it links directly to the abstract of the relevant article - while CO2 Science only show their own interpretation of the studies.
As an example, there is research from the Alps (Mangini et al 2005) which CO2 Science interpret in a weird way and conclude that the MWP was warmer than today. The CO2 Science summary of the study says:
… at three different points during the MWP their data indicate temperature spikes in excess of 1°C above present (1995-1998) temperatures of 1.8°C.
In contrast, it states in the abstract:
…maxima during the Medieval Warm Period between 800 and 1300 AD are in average about 1.7 °C higher than the minima in the Little Ice Age and similar to present-day values.
Another misinterpretation of data can see by looking at the sea temperature data from the Indian Ocean (Oppo et al 2009).
The CO2 Science interpretation reads:
Reconstructed SSTs were, in their words, “warmest from AD 1000 to AD 1250 and during short periods of first millennium.” From the authors' Figure 2b, adapted below, we calculate that the Medieval Warm Period was about 0.4°C warmer than the Current Warm Period.
Then they change the image 2b from the article and make it look like the medieval warming was 0.4 ° C higher than the current warming:
The original graph can be seen below:
As is evident from the 2b in figure 6 above, the mean annual SST for 1997-2007 was higher than the rest of the graph.
It is interesting when these maps point to the data that should show that the medieval warming is unique and greater than the current warming - and use the articles and graphs, as of Paulsen et al 2003 to confirm it:
Here you see a brief Medieval warming around the year 1400 AD. Current warming is pretty clear.
There are some substantial problems with CO2 Science and its sister site Science Skeptical Blog. Various tricks are used to confuse the reader into accepting that the MWP was global and even warmer than the current warming.
For reference geek like me, it is still a goldmine. It has a large collection of articles about paleoclimate - still with the downside that we can't trust the conclusion or the graphs that we see, because of many misrepresentations.
The story is half-told by pointing at a large set of data. Some scientists have actually used some of this data to make comparisons between current warming and the past (Mann et al 2008):
Indeed, one point that people forget when they try to make the most of the MWP: if its temperature was greater than scientists generally believe, there is more warming in the pipeline than scientists expected (see What does past climate change tell us about global warming). That means that the climate sensitivity is greater - and consequently, global warming caused by increased greenhouse gases will be greater. Therefore those arguing that there is no worry about the future of climate change should avoid arguing for a warmer MWP.
Even though there are lot of misrepresentation in the web sites in question, they can be quite helpful in finding the right references, with the good help of Google Scholar for example.