McIntyre: ‘a reductio ad absurdum of tree ring chronologies as useful temperature proxies’
Steve McIntyre has a look at the “revised” PAGES2K temperature proxy dataset that includes tree rings and river sediments. He finds the usual ridiculous problems from the past, such as upside down data and river sediment accumulations that have more to do with building a dam than climate.
There were three “new” proxies: one tree ring series and two lake sediment series. In addition, two tree ring series were updated.
New Tree Ring Proxies
The”new” tree ring series (CAN Composite 15) had, like the other series, been in the Neukom and Gergis 2012 network. For some reason, it had been screened out of the PAGES 2013 network, but now determined to meet the PAGES2K criteria after all. Of the original 63(!) tree ring chronologies in the Neukom and Gergis 2012, only four(!) made their way into the PAGES2017 network. I do not believe for a minute that these four tree ring chronologies are unique thermometers. A more likely interpretation is that their satisfaction of proxy criteria was fortuitous and that they are no more trustworthy as thermometers than the excluded chronologies. Nor did any of these four chronologies reach back to the medieval period: their start dates ranged from 1435 to 1636, start dates, long after the medieval period.
Interestingly, the fresh data in the two updated tree ring series further illustrates the ineffectiveness of these South American tree ring chronologies as temperature proxies, as shown in the plots of Central Andes 6 (CAN 6) and Central Andes 9 (CAN 9) below.
CAN9, which is barely over 300 years long, has high values in mid-20th century, but declines in the last half of the 20th century despite temperatures increase. Its late 20th century decline continues into the 21st century, where values have reverted to the long-term mean. Similarly CAN6 has had little longterm change, but had a late 20th century spike, but has regressed to low values subsequently.
A more plausible interpretation of the data is that these four series were selected ex post because their 20th century values were somewhat higher than values in earlier centuries, but are not magic thermometers.
The tree ring component of this network is, more or less, a reductio ad absurdum of tree ring chronologies as useful temperature proxies: only four of 63 original tree chronologies have sufficient Hockey Stick-ness to be retained in the network, with even these poor remnants reverting to the mean in the 21st century updates. There is negligible similarity between the three lake sediment series, each of which uses a different indicator, though similar measurements appear to have been taken for all three sites. The only series with a meaningful HS (Chepical) appears to result from construction of a dam in 1885AD, rather than from increased temperature. This leaves the Quelccaya ice core series – which was a staple of temperature reconstructions as early as 1998 and, which, ironically, was used upside down in PAGES2K (2013), corrected in PAGES 2017 without disclosure/admission of the earlier error.
All in all, a rather pathetic show by PAGES2K.
Read the full analysis here at Climate Audit
via Watts Up With That? https://ift.tt/1Viafi3