The PAGES2K article to be published tomorrow will show eight regional reconstructions, which are plotted below. In today’s post, I’ll try to briefly summarize what, if anything, is new about them.
Antarctica: This is a composite of 11 isotope series (mostly d18O). It includes some new data (e.g. Steig’s new WAIS series) and some long unavailable data (Ellen Mosley-Thompson’s Plateau Remote). It shows a long-term decline with nothing exceptional in the 20th century. Steig has recently characterized the recent portion of Antarctic isotope as “unusual”, but this is really stretching the facts to the point of disinformation. I’ll post separately on this.
Arctic: This is a somewhat expanded version of the Kaufman data, unsurprising since Kaufman seems to have been the leader of the program. It shows an increase from 1800 to 1950, with leveling off since 1950. Its modern values are higher than medieval values. It is heavy on varvology (22 varve series), but, like Kaufman et al, also has ice cores (16) and tree rings (13, including Briffa’s Yamal) plus a few others. They use Korttajarvi, but Kaufman has issued one correction on this already in 2009 and avoided use of the contaminated portion. We’ve discussed Arctic d18O values from time to time, observing that their 20th century values are rather unexceptional. My surmise is that the varve data, which, as discussed in other CA threads, is highly problematic, is the main contributor to the modern-medieval differential in the PAGES reconstruction.
Asia: This reconstruction is based entirely on tree rings (229 series), all, interestingly, used in a positive orientation. 20th century values are elevated but the reconstruction lacks the distinctive blade of, for example, the Gergis stick. The majority of the tree ring data is unarchived: chronologies have been included in the PAGES2K data, but the underlying measurement remains unarchived.
Australia: this is the Gergis reconstruction. There are only two long series (both tree ring). As is well known, Gergis picked data according to ex post correlation to temperature (contrary to the representation in the disappeared article). The present network is little changed from the network in the disappeared article, with the precise differences remaining to be explained. The network is about half tree ring data and about half is short coral (nearly all O18) data. The blade in the Gergis stick comes almost entirely from coral O18 data – for which corresponding medieval information is lacking. The reconstruction is thus a sort-of splice of low-amplitude tree ring data with high amplitude coral O18. Coral specialist literature nearly always uses Sr data as a measure of temperature. The 20th century increase in coral Sr data is much less than O18 data: however, Gergis screened out the Sr data and almost exclusively used coral O18 data.
Europe: The network is 10 tree ring series and one documentary. I don’t know at present how the series were chosen. Most of the increase in the reconstruction took place prior to 1950. Late 20th century values equal and then exceed mid-century values. It will be interesting to see whether sustained ring widths will be maintained with these particular chronologies during warmer temperatures.
North America. There are two North American reconstructions. A reconstruction using pollen is at 30 year intervals and ends in 1950. It shows elevated temperatures in the late first millennium that exceed the most recent values in the series. The other reconstruction uses tree rings. It includes many series from the MBH98 dataset, including the Graybill bristlecone chronologies. Although the tree ring data is accurately dated, the reconstruction is only reported at 10-year intervals. Although the data set includes new data reaching into the present century, the reconstruction is shown only to 1974.
South America: This network is particularly hard to understand. It shows particularly low medieval values relative to the modern period – a point that is relevant to assertions on medieval-modern differential. The network also uses intrumental data. It has two long ice core series from Quelccaya, which, as previously noted, appear (according to the SI) to have been inverted, a decision which, if correct, would rather detract from conclusions about modern-medieval differential drawn from this reconstruction, given that the medieval portion of the reconstruction only has a few contributors, of which Quelccaya is prominent.